Programming Exercise II: Playing an SOS game

Programming Exercise II: Playing an SOS Game

Absolutely no copying others’ works
(Unlike other languages, using others’ assembly code is obvious.)
Development Requirements
When start developing the exercise, follow the two requirements below:

Have to use the MIPS (Microprocessor without Interlocked Pipeline Stages) assembly language to develop the exercise.
Use the MARS (MIPS Assembler and Runtime Simulator) to test your exercise. The MARS will also be used by the instructor to grade exercises.

Due Date and Submission Method
On or before Thursday, April 02, 2026 and upload the source code (no documentation needed) to the section of “COVID-19 Exams, Homeworks, & Programming Exercises” of Blackboard.

Objective
Design and implement a MIPS assembly program, which has the user play a 6×6 SOS game against the computer. The final program is less than 300 lines without counting the declarations of data structures. The purpose of this exercise is to make students practice assembly language programming including various control instructions, functions, and the runtime stack.

An incomplete game of SOS in an 8×8 board

Rules of an SOS Game
It is a board game for two players who take turns in putting the pieces S and O on empty cells of a board. Before play begins, a square grid of at least 3×3 squares in size is drawn. Players take turns to add either an ‘S’ or an ‘O’ to any square, with no requirement to use the same letter each turn.

The object of the game is for each player to attempt to create the straight sequence S-O-S among connected squares (either diagonally, horizontally, or vertically), and to create as many such sequences as they can. If a player succeeds in creating an SOS, that player immediately takes another turn, and continues to do so until no SOS can be created on their turn. Otherwise turns alternate between players after each move. Keeping track of who made which SOSs can be done by, e.g., one player circling their SOSs and the other player drawing a line through theirs. Once the grid has been filled up, the winner is the player who made the most SOSs. If the grid is filled up and the number of SOSs for each player is the same, then the game is a draw.

Requirements
The 6×6 SOS game includes the following requirements:

(Starting the game: 05%) Use the syscall of MARS to randomly pick either one of the two players, System or User, to start the game.

(Taking turns: 10%) The two players take turns making moves. The player takes another turn if he/she/it creates SOSs.

(SOS numbers: 10%) After each move, show:
- the total number of SOSs created so far, and
- the number of SOSs created by User or System so far.

(Displaying the board: 05%) The board consists of two parts: the game board (left) and the index board (right) as follows:

      . . . . . .     ⇒     0 1 2 3 4 5
      . . . . . .     ⇒     6 7 8 9 a b
      . . . . . .     ⇒     c d e f g h
      . . . . . .     ⇒     i j k l m n
      . . . . . .     ⇒     o p q r s t
      . . . . . .     ⇒     u v w x y z

(User: 10% total) It includes the following features:

(Before the move: 05%) Ask the user whether to stop the game by picking ‘y’ or ‘n’.

(Marking the moves: 05%) Mark a move by entering a piece (either ‘S’ or ‘O’) and an index. For example, if the first move consists of the piece ‘S’ and an index k, the board is displayed as follows:

      . . . . . .     ⇒     0 1 2 3 4 5
      . . . . . .     ⇒     6 7 8 9 a b
      . . . . . .     ⇒     c d e f g h
      . . . . . .     ⇒     i j k l m n
      . . . . . .     ⇒     o p q r s t
      . . . . . .     ⇒     u v w x y z

                    ⇓ S at k

      . . . . . .     ⇒     0 1 2 3 4 5
      . . . . . .     ⇒     6 7 8 9 a b
      . . . . . .     ⇒     c d e f g h
      . . S . . .     ⇒     i j k l m n
      . . . . . .     ⇒     o p q r s t
      . . . . . .     ⇒     u v w x y z

(System: 35% total) It includes the following features:
- (Before the move: 05%) Start the move after the spacebar is hit (including the move after an SOS is created).
- (One-step lookahead move: 10%) Take the next move based on the method of one-step lookahead moves. That is the move will create the highest number of SOSs among all possible one-step moves. For example, the next move for the following game board:
```
      . . . . . .     ⇒     0 1 2 3 4 5
      . . O S . .     ⇒     6 7 8 9 a b
      . . S O . .     ⇒     c d e f g h
      . . O S O .     ⇒     i j k l m n
      . . S O S .     ⇒     o p q r s t
      . . . . . .     ⇒     u v w x y z
```
  is the piece ‘S’ at the index g since it will create two SOSs as follows:
```
      . . . . . .     ⇒     0 1 2 3 4 5
      . . O S . .     ⇒     6 7 8 9 a b
      . . S O S .     ⇒     c d e f g h
      . . O S O .     ⇒     i j k l m n
      . . S O S .     ⇒     o p q r s t
      . . . . . .     ⇒     u v w x y z
```
  Other moves create at most one SOS each.
- (Random moves: 10%) If it is not possible to create SOSs, randomly generate the next move.
- (Showing and marking the moves: 10%) Show and mark a move including the piece (either ‘S’ or ‘O’) and an index (0..z).

(Ending: 25% total) Perform the following tasks after the user does not want to continue or the grid has been filled up:
- (Result: 10%) Declare the winner or a tied game.
- (SOS numbers: 10%) Show the SOS number created by each.
- (New game: 05%) Start a new game after the user picks ‘y’.

Programming Hints
The four essential components of software are (i) algorithms, (ii) data structures, (iii) programming languages, and (iv) code, where algorithms are the most critical one. In addition, using appropriate data structures could save a great deal of coding work, especially for assembly coding. The following hints are from the instructor and you do not necessarily have to use them:

To represent the game board, a 6×6 grid:

      . . . . . .     ⇒     0 1 2 3 4 5
      . . . . . .     ⇒     6 7 8 9 a b
      . . . . . .     ⇒     c d e f g h
      . . . . . .     ⇒     i j k l m n
      . . . . . .     ⇒     o p q r s t
      . . . . . .     ⇒     u v w x y z

the instructor uses the following string:

     board:   .ascii   "\n\n    . . . . . .      0 1 2 3 4 5"
              .ascii     "\n    . . . . . .      6 7 8 9 a b"
              .ascii     "\n    . . . . . .      c d e f g h"
              .ascii     "\n    . . . . . .      i j k l m n"
              .ascii     "\n    . . . . . .      o p q r s t"
              .asciiz    "\n    . . . . . .      u v w x y z\n"

Also, the instructor uses the following command to represent the offsets:

     offset:  .half     6,   8,  10,  12,  14,  16  
              .half    39,  41,  43,  45,  47,  49
              .half    72,  74,  76,  78,  80,  82
              .half   105, 107, 109, 111, 113, 115
              .half   138, 140, 142, 144, 146, 148
              .half   171, 173, 175, 177, 179, 181

where

the numbers are offsets (not assembly code),
the new line, ‘\n’, is one byte long, and
each offset uses 2 bytes because the range of 1 byte, [-128 – 127], is not enough for a number ≥ 128.

Convert the character indexes 0–9a–z to integer indexes 0–35, respectively. Assuming the converted index is in $t0, the following code then puts the piece ‘S’ at that location:

     mul  $t0, $t0, 2        # Each offset is two-byte long.
     lh   $t1, offset($t0)   # Load $t1 with the offset of the index $t0.
     li   $t2, 'S'           # Put the piece ‘S’ in $t2.
     sb   $t2, board($t1)    # Put the piece at the location, board+offset.

Since the grading is mainly based on the testing results without considering much about performance and algorithms, the instructor uses the following data structure to count the number of SOSs created. All possible SOSs are listed as follows^‡:

     SOS:    .ascii   "012"      # 0
             .ascii   "07e"      # 1
             .ascii   "06c"      # 2
             .ascii   "123"      # 3
             .ascii   "18f"      # 4
             .ascii   "17d"      # 5
             .ascii   "234"      # 6
             .ascii   "29g"      # 7 
             .ascii   "28e"      # 8
             .ascii   "27c"      # 9
             .ascii   "345"      # 10
             .ascii   "3ah"      # 11
             .ascii   "39f"      # 12
             .ascii   "38d"      # 13
             .ascii   "4ag"      # 14
             .ascii   "49e"      # 15
             .ascii   "5bh"      # 16
             .ascii   "5af"      # 17
             .ascii   "678"      # 18
             .ascii   "6dk"      # 19
             .ascii   "6ci"      # 20
             .ascii   "789"      # 21
             .ascii   "7el"      # 22
             .ascii   "7dj"      # 23
             .ascii   "89a"      # 24
             .ascii   "8fm"      # 25
             .ascii   "8ek"      # 26
             .ascii   "8di"      # 27
             .ascii   "9ab"      # 28
             .ascii   "9gn"      # 29
             .ascii   "9fl"      # 30
             .ascii   "9ej"      # 31
             .ascii   "agm"      # 32
             .ascii   "afk"      # 33
             .ascii   "bhn"      # 34
             .ascii   "bgl"      # 35
             .ascii   "cde"      # 36
             .ascii   "cjq"      # 37
             .ascii   "cio"      # 38
             .ascii   "def"      # 39
             .ascii   "dkr"      # 40
             .ascii   "djp"      # 41
             .ascii   "efg"      # 42
             .ascii   "els"      # 43
             .ascii   "ekq"      # 44
             .ascii   "ejo"      # 45
             .ascii   "fgh"      # 46
             .ascii   "fmt"      # 47
             .ascii   "flr"      # 48
             .ascii   "fkp"      # 49
             .ascii   "gms"      # 50
             .ascii   "glq"      # 51
             .ascii   "hnt"      # 52
             .ascii   "hmr"      # 53
             .ascii   "ijk"      # 54
             .ascii   "ipw"      # 55
             .ascii   "iou"      # 56
             .ascii   "jkl"      # 57
             .ascii   "jqx"      # 58
             .ascii   "jpv"      # 59
             .ascii   "klm"      # 60
             .ascii   "kry"      # 61
             .ascii   "kqw"      # 62
             .ascii   "kpu"      # 63
             .ascii   "lmn"      # 64
             .ascii   "lsz"      # 65
             .ascii   "lrx"      # 66
             .ascii   "lqv"      # 67
             .ascii   "msy"      # 68
             .ascii   "mrw"      # 69
             .ascii   "ntz"      # 70
             .ascii   "nsx"      # 71
             .ascii   "opq"      # 72
             .ascii   "pqr"      # 73
             .ascii   "qrs"      # 74
             .ascii   "rst"      # 75
             .ascii   "uvw"      # 76
             .ascii   "vwx"      # 77
             .ascii   "wxy"      # 78
             .ascii   "xyz"      # 79

where each three characters are the indexes of the three pieces in a row. For example, the SOS #70 is an SOS sequence if

     board(n) = 'S'
     board(t) = 'O'
     board(z) = 'S'

^‡Note that the instructor has tried his best to make the list complete, but could not 100% guarantee its correctness or completeness.

The random number generator can be found from the syscall of MARS such as:

       xor  $a0, $a0, $a0     # Set a seed number.
       li   $a1, 36           # random number 0 to 35
       li   $v0, 42           # random number generator
       syscall

Using subroutines can reduce repeated code. An example of how to call the subroutine routine1 is given as follows:
```
          jal   routine1      # Jump and link to routine1
   next:  
          ...
```
where the label next is not required. The following command in the subroutine routine1 will return the control back to the next, the next command after the “jal routine1”:
```
   routine1:
          ...
          jr    $ra           # Jump to the contents of $ra
```
where the return address is saved in the register $31 or $ra

When a subroutine calls another subroutine, the return address, $31 or $ra, has to be saved before making the call^‡. The return address is restored after the called subroutine returns. The instructor uses the runtime stack to save the return addresses, so deep subroutine calls are supported. Use the following two commands to push the $ra to the runtime stack:
```
       subu  $sp, $sp, 4      # Decrement the $sp to make space for $ra.
       sw    $ra, ($sp)       # Push the return address, $ra.
```
and use the following two commands to pop up the $ra from the runtime stack:
```
       lw    $ra, ($sp)       # Pop the return address, $ra.
       addu  $sp, $sp, 4      # Increment the $sp.
```
There are many ways to find the system’s next move. This exercise asks you to use the method of one-step lookahead moves. Instead of using complicated calculations, the instructor lists all possible moves and selects the best one. This is not an efficient way to solve the problem, but the efficiency issue will be considered minimally when grading.

Sample code of taking a one-step lookahead move is given below for your reference:

Lookahead.asm

#
# Finding the next move by using a one-step lookahead method
#
        .data
p1:     .asciiz  "\n\nA one-step lookahead method for the next move:"
p2:     .asciiz  "\nThe next move: "
p3:     .asciiz  "\nNumber of total SOSs: "
p4:     .asciiz  "\nNumber of added SOSs: "
maxMov: .byte    0        # the move [0..z] having the max SOS #
maxSOS: .byte    0        # max SOS #

board:  .ascii   "\n\n    . S . S O S      0 1 2 3 4 5"
        .ascii     "\n    S O S . . .      6 7 8 9 a b"
        .ascii     "\n    . S O S . .      c d e f g h"
        .ascii     "\n    . . . . . .      i j k l m n"
        .ascii     "\n    . . . . . .      o p q r s t"
        .asciiz    "\n    . . . . . .      u v w x y z\n"

offset: .half     6,   8,  10,  12,  14,  16
        .half    39,  41,  43,  45,  47,  49
        .half    72,  74,  76,  78,  80,  82
        .half   105, 107, 109, 111, 113, 115
        .half   138, 140, 142, 144, 146, 148
        .half   171, 173, 175, 177, 179, 181

SOS:    .ascii  "012"     #  0
        .ascii  "07e"     #  1
        .ascii  "06c"     #  2
        .ascii  "123"     #  3
        .ascii  "18f"     #  4
        .ascii  "17d"     #  5
        .ascii  "234"     #  6
        .ascii  "29g"     #  7
        .ascii  "28e"     #  8
        .ascii  "27c"     #  9
        .ascii  "345"     # 10
        .ascii  "3ah"     # 11
        .ascii  "39f"     # 12
        .ascii  "38d"     # 13
        .ascii  "4ag"     # 14
        .ascii  "49e"     # 15
        .ascii  "5bh"     # 16
        .ascii  "5af"     # 17
        .ascii  "678"     # 18
        .ascii  "6dk"     # 19
        .ascii  "6ci"     # 20
        .ascii  "789"     # 21
        .ascii  "7el"     # 22
        .ascii  "7dj"     # 23
        .ascii  "89a"     # 24
        .ascii  "8fm"     # 25
        .ascii  "8ek"     # 26
        .ascii  "8di"     # 27
        .ascii  "9ab"     # 28
        .ascii  "9gn"     # 29
        .ascii  "9fl"     # 30
        .ascii  "9ej"     # 31
        .ascii  "agm"     # 32
        .ascii  "afk"     # 33
        .ascii  "bhn"     # 34
        .ascii  "bgl"     # 35
        .ascii  "cde"     # 36
        .ascii  "cjq"     # 37
        .ascii  "cio"     # 38
        .ascii  "def"     # 39
        .ascii  "dkr"     # 40
        .ascii  "djp"     # 41
        .ascii  "efg"     # 42
        .ascii  "els"     # 43
        .ascii  "ekq"     # 44
        .ascii  "ejo"     # 45
        .ascii  "fgh"     # 46
        .ascii  "fmt"     # 47
        .ascii  "flr"     # 48
        .ascii  "fkp"     # 49
        .ascii  "gms"     # 50
        .ascii  "glq"     # 51
        .ascii  "hnt"     # 52
        .ascii  "hmr"     # 53
        .ascii  "ijk"     # 54
        .ascii  "ipw"     # 55
        .ascii  "iou"     # 56
        .ascii  "jkl"     # 57
        .ascii  "jqx"     # 58
        .ascii  "jpv"     # 59
        .ascii  "klm"     # 60
        .ascii  "kry"     # 61
        .ascii  "kqw"     # 62
        .ascii  "kpu"     # 63
        .ascii  "lmn"     # 64
        .ascii  "lsz"     # 65
        .ascii  "lrx"     # 66
        .ascii  "lqv"     # 67
        .ascii  "msy"     # 68
        .ascii  "mrw"     # 69
        .ascii  "ntz"     # 70
        .ascii  "nsx"     # 71
        .ascii  "opq"     # 72
        .ascii  "pqr"     # 73
        .ascii  "qrs"     # 74
        .ascii  "rst"     # 75
        .ascii  "uvw"     # 76
        .ascii  "vwx"     # 77
        .ascii  "wxy"     # 78
        .ascii  "xyz"     # 79

        .text
        .globl main
#
##########################  Main Program  #######################
#
main:
        # Print the Prompt p1, greeting.
        la    $a0, p1
        li    $v0, 4
        syscall
  
        # Print the board.
        la    $a0, board
        li    $v0, 4
        syscall

        # Declarations
        move  $t0, $0            # $t0: SOS index [0..239] where 239 = 3*80 - 1
        move  $t1, $0            # $t1: SOS range [0..79]
        move  $t2, $0            # $t2: previous total SOS #
        move  $t3, $0            # $t3: current total SOS #
        move  $t4, $0            # $t4: current board index [0..35]

        # Checking next SOS
L1:     jal   CheckSOS
        beqz  $v0, L2
        add   $t2, $t2, 1 
L2:     add   $t0, $t0, 1
        add   $t1, $t1, 1
        ble   $t1, 79, L1
        
        move  $t4, $0
L3:     mul   $t5, $t4, 2        # Each offset is two-byte long.
        lh    $t5, offset($t5)   # Load $t1 with the offset of the index $t0.
        lb    $t6, board($t5)
        beq   $t6, '.', L4
        add   $t4, $t4, 1        # The board at index is not empty.
        j     L3
            
L4:     li    $t6, 'S'           # Put the piece ‘S’ in $t2.
        sb    $t6, board($t5)    # Put the piece at the location, board+offset.

        # Reset
        move  $t0, $0            # $t0: SOS index [0..239] where 239 = 3*80 - 1
        move  $t1, $0            # $t1: SOS range [0..79]
        move  $t3, $0            # $t3: current total SOS #
                
        # Checking next SOS
L5:     jal   CheckSOS
        beqz  $v0, L6
        add   $t3, $t3, 1
         
L6:     add   $t0, $t0, 1
        add   $t1, $t1, 1
        ble   $t1, 79, L5

        lb    $t6, maxSOS
        ble   $t3, $t6, L7
        sb    $t3, maxSOS
        sb    $t4, maxMov
             
        # Reset the board.
L7:     mul   $t6, $t4, 2        # Each offset is two-byte long.
        lh    $t7, offset($t6)   # Load $t1 with the offset of the index $t0.
        li    $t8, '.'           # Put the piece ‘.’ in $t2.
        sb    $t8, board($t7)    # Put the piece at the location, board+offset.
   
        add   $t4, $t4, 1
        ble   $t4, 35, L3
        
        lb    $t5, maxMov     
        # Mark the board.
        mul   $t6, $t5, 2        # Each offset is two-byte long.
        lh    $t7, offset($t6)   # Load $t1 with the offset of the index $t0.
        li    $t8, 'S'           # Put the piece ‘S’ in $t2.
        sb    $t8, board($t7)    # Put the piece at the location, board+offset.
 
        la    $a0, p2
        li    $v0, 4
        syscall        
        move  $a0, $t5           # Print the max move.
        jal   I2C
        li    $v0, 11
        syscall
        
        la    $a0, p3
        li    $v0, 4
        syscall
        lb    $a0, maxSOS        # Print the max SOS #.
        li    $v0, 1
        syscall 

        la    $a0, p4
        li    $v0, 4
        syscall
        lb    $t3, maxSOS
        sub   $a0, $t3, $t2      # Print the added SOS #.
        li    $v0, 1
        syscall 

        la    $a0, board
        li    $v0, 4
        syscall
             
        # End of program
End:    li    $v0, 10
        syscall

#
##############  Check whether 'SOS' exists.  ##################
#
# Input: $t0 (integer [0..239], SOS index)
# Output: $v0 (1: SOS found, 0: SOS not found)
#
  
CheckSOS: 
        subu  $sp, $sp, 4      # Decrement the $sp to make space for $ra.
        sw    $ra, ($sp)       # Push the return address, $ra.
        subu  $sp, $sp, 4      # Decrement the $sp to make space for $t1.
        sw    $t1, ($sp)       # Push the $t1.
        
        li    $v0, 0       
        # Checking 'S'
        lb    $a0, SOS($t0)
        jal   C2I
        mul   $t1, $a0, 2
        lh    $t1, offset($t1)
        lb    $t1, board($t1)
        beq   $t1, 'S', L11
        add   $t0, $t0, 2
        j     L13

        # Checking 'O'
L11:    add   $t0, $t0, 1
        lb    $a0, SOS($t0)
        jal   C2I
        mul   $t1, $a0, 2
        lh    $t1, offset($t1)
        lb    $t1, board($t1)
        beq   $t1, 'O', L12
        add   $t0, $t0, 1
        j     L13

        # Checking 'S'
L12:    add   $t0, $t0, 1
        lb    $a0, SOS($t0)
        jal   C2I
        mul   $t1, $a0, 2
        lh    $t1, offset($t1)
        lb    $t1, board($t1)
        bne   $t1, 'S', L13
        li    $v0, 1           # An SOS found

L13:    lw    $t1, ($sp)       # Pop $t1.
        addu  $sp, $sp, 4      # Increment the $sp.
        lw    $ra, ($sp)       # Pop the return address, $ra.
        addu  $sp, $sp, 4      # Increment the $sp.
        jr    $ra              # Return.

#
##############  Convert character [0..z] to integer [0..35].  ##################
#
# Input: $a0 (character [0..z])
# Output: $a0 (integer [0..35])
#
  
C2I:    blt   $a0, '0', L20
        bgt   $a0, '9', L20
        sub   $a0, $a0, '0'
        j     L21
L20:    sub   $a0, $a0, 'a'
        add   $a0, $a0, 10
L21:    jr    $ra              # Return.

#
##############  Convert integer [0..35] to character [0..z].  ##################
#
# Input: $a0 (integer [0..35])
# Output: $a0 (character [0..z])
#
  
I2C:    bgt   $a0, 9, L30
        add   $a0, $a0, '0'
        j     L31
L30:    sub   $a0, $a0, 10
        add   $a0, $a0, 'a'
L31:    jr    $ra              # Return.

An Example of Lookahead.asm Execution

Find the next move by using a one-step lookahead method:

    . . . . . .      0 1 2 3 4 5
    . . . O . .      6 7 8 9 a b
    . S O O O .      c d e f g h
    . . S O S .      i j k l m n
    . . S . . .      o p q r s t
    . . . . . .      u v w x y z

The next move: 8
Number of total SOSs: 3
Number of added SOSs: 2

    . . . . . .      0 1 2 3 4 5
    . . S O . .      6 7 8 9 a b
    . S O O O .      c d e f g h
    . . S O S .      i j k l m n
    . . S . . .      o p q r s t
    . . . . . .      u v w x y z

-- program is finished running --

Find the next move by using a one-step lookahead method:

    . . . . . .      0 1 2 3 4 5
    . . . O S .      6 7 8 9 a b
    . . S O O .      c d e f g h
    . . S O . .      i j k l m n
    . . S . . .      o p q r s t
    . . . . . .      u v w x y z

The next move: m
Number of total SOSs: 3
Number of added SOSs: 2

    . . . . . .      0 1 2 3 4 5
    . . . O S .      6 7 8 9 a b
    . . S O O .      c d e f g h
    . . S O S .      i j k l m n
    . . S . . .      o p q r s t
    . . . . . .      u v w x y z

-- program is finished running --

Find the next move by using a one-step lookahead method:

    . . . . . .      0 1 2 3 4 5
    . . S O . .      6 7 8 9 a b
    . . S O O .      c d e f g h
    . . S O S .      i j k l m n
    . . . . . .      o p q r s t
    . . . . . .      u v w x y z

The next move: a
Number of total SOSs: 5
Number of added SOSs: 3

    . . . . . .      0 1 2 3 4 5
    . . S O S .      6 7 8 9 a b
    . . S O O .      c d e f g h
    . . S O S .      i j k l m n
    . . . . . .      o p q r s t
    . . . . . .      u v w x y z

-- program is finished running --

Find the next move by using a one-step lookahead method:

    . . . . . .      0 1 2 3 4 5
    . O S . . .      6 7 8 9 a b
    S . S S O .      c d e f g h
    . . . O . .      i j k l m n
    . S O . . .      o p q r s t
    . . . . . .      u v w x y z

The next move: r
Number of total SOSs: 2
Number of added SOSs: 2

    . . . . . .      0 1 2 3 4 5
    . O S . . .      6 7 8 9 a b
    S . S S O .      c d e f g h
    . . . O . .      i j k l m n
    . S O S . .      o p q r s t
    . . . . . .      u v w x y z

-- program is finished running --

Examples
The following list shows some execution examples, where the white, italic text with a black background color is entered by users:

Examples of Exercise II Execution

Start Playing an SOS Game:

    . . . . . .      0 1 2 3 4 5
    . . . . . .      6 7 8 9 a b
    . . . . . .      c d e f g h
    . . . . . .      i j k l m n
    . . . . . .      o p q r s t
    . . . . . .      u v w x y z

I (System) am first and I pick the piece S
The move from me is m
Number of total SOSs created so far: 0
Number of SOSs created by me so far: 0

    . . . . . .      0 1 2 3 4 5
    . . . . . .      6 7 8 9 a b
    . . . . . .      c d e f g h
    . . . . S .      i j k l m n
    . . . . . .      o p q r s t
    . . . . . .      u v w x y z

Continue? (y/n)  y  
Your turn.  You (User) pick a piece: (S|O)  O 
Enter your next move: [0..z]  a 
Number of total SOSs created so far: 0
Number of SOSs created by you so far: 0

    . . . . . .      0 1 2 3 4 5
    . . . . O .      6 7 8 9 a b
    . . . . . .      c d e f g h
    . . . . S .      i j k l m n
    . . . . . .      o p q r s t
    . . . . . .      u v w x y z

Hit the spacebar to start the System’s next move.
 
My turn.  I (System) pick the piece O
The move from me is 8
Number of total SOSs created so far: 0
Number of SOSs created by me so far: 0

    . . . . . .      0 1 2 3 4 5
    . . O . O .      6 7 8 9 a b
    . . . . . .      c d e f g h
    . . . . S .      i j k l m n
    . . . . . .      o p q r s t
    . . . . . .      u v w x y z

Continue? (y/n)  y 
Your turn.  You (User) pick a piece: (S|O)  O 
Enter your next move: [0..z]  1 
Number of total SOSs created so far: 0
Number of SOSs created by you so far: 0

    . O . . . .      0 1 2 3 4 5
    . . O . O .      6 7 8 9 a b
    . . . . . .      c d e f g h
    . . . . S .      i j k l m n
    . . . . . .      o p q r s t
    . . . . . .      u v w x y z

Hit the spacebar to start the System’s next move.
  
My turn.  I (System) pick the piece S
The move from me is t
Number of total SOSs created so far: 0
Number of SOSs created by me so far: 0

    . O . . . .      0 1 2 3 4 5
    . . O . O .      6 7 8 9 a b
    . . . . . .      c d e f g h
    . . . . S .      i j k l m n
    . . . . . S      o p q r s t
    . . . . . .      u v w x y z

Continue? (y/n)  y 
Your turn.  You (User) pick a piece: (S|O)  O 
Enter your next move: [0..z]  o 
Number of total SOSs created so far: 0
Number of SOSs created by you so far: 0

    . O . . . .      0 1 2 3 4 5
    . . O . O .      6 7 8 9 a b
    . . . . . .      c d e f g h
    . . . . S .      i j k l m n
    O . . . . S      o p q r s t
    . . . . . .      u v w x y z

Hit the spacebar to start the System’s next move.
  
My turn.  I (System) pick the piece S
The move from me is x
Number of total SOSs created so far: 0
Number of SOSs created by me so far: 0

    . O . . . .      0 1 2 3 4 5
    . . O . O .      6 7 8 9 a b
    . . . . . .      c d e f g h
    . . . . S .      i j k l m n
    O . . . . S      o p q r s t
    . . . S . .      u v w x y z

Continue? (y/n)  y 
Your turn.  You (User) pick a piece: (S|O)  O 
Enter your next move: [0..z]  h 
Number of total SOSs created so far: 0
Number of SOSs created by you so far: 0

    . O . . . .      0 1 2 3 4 5
    . . O . O .      6 7 8 9 a b
    . . . . . O      c d e f g h
    . . . . S .      i j k l m n
    O . . . . S      o p q r s t
    . . . S . .      u v w x y z

Hit the spacebar to start the System’s next move.
  
My turn.  I (System) pick the piece S
The move from me is 3
Number of total SOSs created so far: 0
Number of SOSs created by me so far: 0

    . O . S . .      0 1 2 3 4 5
    . . O . O .      6 7 8 9 a b
    . . . . . O      c d e f g h
    . . . . S .      i j k l m n
    O . . . . S      o p q r s t
    . . . S . .      u v w x y z

Continue? (y/n)  y 
Your turn.  You (User) pick a piece: (S|O)  S 
Enter your next move: [0..z]  d 
Number of total SOSs created so far: 1
Number of SOSs created by you so far: 1

    . O . S . .      0 1 2 3 4 5
    . . O . O .      6 7 8 9 a b
    . S . . . O      c d e f g h
    . . . . S .      i j k l m n
    O . . . . S      o p q r s t
    . . . S . .      u v w x y z

Continue? (y/n)  y 
Your turn.  You (User) pick a piece: (S|O)  S 
Enter your next move: [0..z]  k 
Number of total SOSs created so far: 1
Number of SOSs created by you so far: 1

    . O . S . .      0 1 2 3 4 5
    . . O . O .      6 7 8 9 a b
    . S . . . O      c d e f g h
    . . S . S .      i j k l m n
    O . . . . S      o p q r s t
    . . . S . .      u v w x y z

Hit the spacebar to start the System’s next move.
  
My turn.  I (System) pick the piece O
The move from me is l
Number of total SOSs created so far: 2
Number of SOSs created by me so far: 1

    . O . S . .      0 1 2 3 4 5
    . . O . O .      6 7 8 9 a b
    . S . . . O      c d e f g h
    . . S O S .      i j k l m n
    O . . . . S      o p q r s t
    . . . S . .      u v w x y z

Hit the spacebar to start the System’s next move.
 
My turn.  I (System) pick the piece O
The move from me is v
Number of total SOSs created so far: 2
Number of SOSs created by me so far: 1

    . O . S . .      0 1 2 3 4 5
    . . O . O .      6 7 8 9 a b
    . S . . . O      c d e f g h
    . . S O S .      i j k l m n
    O . . . . S      o p q r s t
    . O . S . .      u v w x y z

Continue? (y/n)  n 

A tied game!  I (System) have 1 SOSs and you (User) have 1 SOSs.
New game? (y/n)  y 

Start Playing an SOS Game:

    . . . . . .      0 1 2 3 4 5
    . . . . . .      6 7 8 9 a b
    . . . . . .      c d e f g h
    . . . . . .      i j k l m n
    . . . . . .      o p q r s t
    . . . . . .      u v w x y z

I (System) am first and I pick the piece O
The move from me is 5
Number of total SOSs created so far: 0
Number of SOSs created by me so far: 0

    . . . . . O      0 1 2 3 4 5
    . . . . . .      6 7 8 9 a b
    . . . . . .      c d e f g h
    . . . . . .      i j k l m n
    . . . . . .      o p q r s t
    . . . . . .      u v w x y z

Continue? (y/n)  y 
Your turn.  You (User) pick a piece: (S|O)  S 
Enter your next move: [0..z]  h 
Number of total SOSs created so far: 0
Number of created SOSs by me so far: 0

    . . . . . O      0 1 2 3 4 5
    . . . . . .      6 7 8 9 a b
    . . . . . S      c d e f g h
    . . . . . .      i j k l m n
    . . . . . .      o p q r s t
    . . . . . .      u v w x y z

Hit the spacebar to start the System’s next move.
  
My turn.  I (System) pick the piece O
The move from me is 6
Number of total SOSs created so far: 0
Number of created SOSs by me so far: 0

    . . . . . O      0 1 2 3 4 5
    O . . . . .      6 7 8 9 a b
    . . . . . S      c d e f g h
    . . . . . .      i j k l m n
    . . . . . .      o p q r s t
    . . . . . .      u v w x y z

Continue? (y/n)  y 
Your turn.  You (User) pick a piece: (S|O)  S 
Enter your next move: [0..z]  o 
Number of total SOSs created so far: 0
Number of SOSs created by you so far: 0

    . . . . . O      0 1 2 3 4 5
    O . . . . .      6 7 8 9 a b
    . . . . . S      c d e f g h
    . . . . . .      i j k l m n
    S . . . . .      o p q r s t
    . . . . . .      u v w x y z

Hit the spacebar to start the System’s next move.
  
My turn.  I (System) pick the piece O
The move from me is a
Number of total SOSs created so far: 0
Number of SOSs created by me so far: 0

    . . . . . O      0 1 2 3 4 5
    O . . . O .      6 7 8 9 a b
    . . . . . S      c d e f g h
    . . . . . .      i j k l m n
    S . . . . .      o p q r s t
    . . . . . .      u v w x y z

Continue? (y/n)  y 
Your turn.  You (User) pick a piece: (S|O)  S 
Enter your next move: [0..z]  3 
Number of total SOSs created so far: 1
Number of SOSs created by you so far: 1

    . . . S . O      0 1 2 3 4 5
    O . . . O .      6 7 8 9 a b
    . . . . . S      c d e f g h
    . . . . . .      i j k l m n
    S . . . . .      o p q r s t
    . . . . . .      u v w x y z

Continue? (y/n)  y 
Your turn.  You (User) pick a piece: (S|O)  S 
Enter your next move: [0..z]  y 
Number of total SOSs created so far: 1
Number of SOSs created by you so far: 1

    . . . S . O      0 1 2 3 4 5
    O . . . O .      6 7 8 9 a b
    . . . . . S      c d e f g h
    . . . . . .      i j k l m n
    S . . . . .      o p q r s t
    . . . . S .      u v w x y z

Hit the spacebar to start the System’s next move.
  
My turn.  I (System) pick the piece S
The move from me is x
Number of total SOSs created so far: 1
Number of SOSs created by me so far: 0

    . . . S . O      0 1 2 3 4 5
    O . . . O .      6 7 8 9 a b
    . . . . . S      c d e f g h
    . . . . . .      i j k l m n
    S . . . . .      o p q r s t
    . . . S S .      u v w x y z

Continue? (y/n)  y 
Your turn.  You (User) pick a piece: (S|O)  S 
Enter your next move: [0..z]  8 
Number of total SOSs created so far: 1
Number of SOSs created by you so far: 1

    . . . S . O      0 1 2 3 4 5
    O . S . O .      6 7 8 9 a b
    . . . . . S      c d e f g h
    . . . . . .      i j k l m n
    S . . . . .      o p q r s t
    . . . S S .      u v w x y z

Hit the spacebar to start the System’s next move.
  
My turn.  I (System) pick the piece O
The move from me is q
Number of total SOSs created so far: 1
Number of SOSs created by me so far: 0

    . . . S . O      0 1 2 3 4 5
    O . S . O .      6 7 8 9 a b
    . . . . . S      c d e f g h
    . . . . . .      i j k l m n
    S . O . . .      o p q r s t
    . . . S S .      u v w x y z

Continue? (y/n)  y 
Your turn.  You (User) pick a piece: (S|O)  S 
Enter your next move: [0..z]  j 
Number of total SOSs created so far: 2
Number of SOSs created by you so far: 2

    . . . S . O      0 1 2 3 4 5
    O . S . O .      6 7 8 9 a b
    . . . . . S      c d e f g h
    . S . . . .      i j k l m n
    S . O . . .      o p q r s t
    . . . S S .      u v w x y z

Continue? (y/n)  y 
Your turn.  You (User) pick a piece: (S|O)  O 
Enter your next move: [0..z]  f 
Number of total SOSs created so far: 2
Number of SOSs created by you so far: 2

    . . . S . O      0 1 2 3 4 5
    O . S . O .      6 7 8 9 a b
    . . . O . S      c d e f g h
    . S . . . .      i j k l m n
    S . O . . .      o p q r s t
    . . . S S .      u v w x y z

Hit the spacebar to start the System’s next move.
  
My turn.  I (System) pick the piece S
The move from me is m
Number of total SOSs created so far: 3
Number of SOSs created by me so far: 1

    . . . S . O      0 1 2 3 4 5
    O . S . O .      6 7 8 9 a b
    . . . O . S      c d e f g h
    . S . . S .      i j k l m n
    S . O . . .      o p q r s t
    . . . S S .      u v w x y z

Hit the spacebar to start the System’s next move.
 
My turn.  I (System) pick the piece O
The move from me is s
Number of total SOSs created so far: 4
Number of SOSs created by me so far: 2

    . . . S . O      0 1 2 3 4 5
    O . S . O .      6 7 8 9 a b
    . . . O . S      c d e f g h
    . S . . S .      i j k l m n
    S . O . O .      o p q r s t
    . . . S S .      u v w x y z

Hit the spacebar to start the System’s next move.
  
My turn.  I (System) pick the piece S
The move from me is n
Number of total SOSs created so far: 5
Number of SOSs created by me so far: 3

    . . . S . O      0 1 2 3 4 5
    O . S . O .      6 7 8 9 a b
    . . . O . S      c d e f g h
    . S . . S S      i j k l m n
    S . O . O .      o p q r s t
    . . . S S .      u v w x y z

Hit the spacebar to start the System’s next move.
  
My turn.  I (System) pick the piece  S 
The move from me is  l 
Number of total SOSs created so far: 5
Number of SOSs created by me so far: 3

    . . . S . O      0 1 2 3 4 5
    O . S . O .      6 7 8 9 a b
    . . . O . S      c d e f g h
    . S . S S S      i j k l m n
    S . O . O .      o p q r s t
    . . . S S .      u v w x y z

Continue? (y/n)  y 
Your turn.  You (User) pick a piece: (S|O)  O 
Enter your next move: (0..z)  r 
Number of total SOSs created so far: 6
Number of SOSs created by you so far: 3

    . . . S . O      0 1 2 3 4 5
    O . S . O .      6 7 8 9 a b
    . . . O . S      c d e f g h
    . S . S S S      i j k l m n
    S . O O O .      o p q r s t
    . . . S S .      u v w x y z

Continue? (y/n)  y 
Your turn.  You (User) pick a piece: (S|O)  S 
Enter your next move: (0..z)  z 
Number of total SOSs created so far: 7
Number of SOSs created by you so far: 4

    . . . S . O      0 1 2 3 4 5
    O . S . O .      6 7 8 9 a b
    . . . O . S      c d e f g h
    . S . S S S      i j k l m n
    S . O O O .      o p q r s t
    . . . S S S      u v w x y z

Continue? (y/n)  y 
Your turn.  You (User) pick a piece: (S|O)  O 
Enter your next move: (0..z)  v 
Number of total SOSs created so far: 7
Number of SOSs created by you so far: 4

    . . . S . O      0 1 2 3 4 5
    O . S . O .      6 7 8 9 a b
    . . . O . S      c d e f g h
    . S . S S S      i j k l m n
    S . O O O .      o p q r s t
    . O . S S S      u v w x y z

Hit the spacebar to start the System’s next move.
 
My turn.  I (System) pick the piece S
The move from me is w
Number of total SOSs created so far: 8
Number of SOSs created by me so far: 4

    . . . S . O      0 1 2 3 4 5
    O . S . O .      6 7 8 9 a b
    . . . O . S      c d e f g h
    . S . S S S      i j k l m n
    S . O O O .      o p q r s t
    . O S S S S      u v w x y z

Hit the spacebar to start the System’s next move.

My turn.  I (System) pick the piece S
The move from me is k
Number of total SOSs created so far: 10
Number of SOSs created by me so far: 6

    . . . S . O      0 1 2 3 4 5
    O . S . O .      6 7 8 9 a b
    . . . O . S      c d e f g h
    . S S S S S      i j k l m n
    S . O O O .      o p q r s t
    . O S S S S      u v w x y z

Hit the spacebar to start the System’s next move.
 
My turn.  I (System) pick the piece S
The move from me is u
Number of total SOSs created so far: 11
Number of SOSs created by me so far: 7

    . . . S . O      0 1 2 3 4 5
    O . S . O .      6 7 8 9 a b
    . . . O . S      c d e f g h
    . S S S S S      i j k l m n
    S . O O O .      o p q r s t
    S O S S S S      u v w x y z

Hit the spacebar to start the System’s next move.
 
My turn.  I (System) pick the piece S
The move from me is 9
Number of total SOSs created so far: 12
Number of SOSs created by me so far: 8

    . . . S . O      0 1 2 3 4 5
    O . S S O .      6 7 8 9 a b
    . . . O . S      c d e f g h
    . S S S S S      i j k l m n
    S . O O O .      o p q r s t
    S O S S S S      u v w x y z

Hit the spacebar to start the System’s next move.
 
My turn.  I (System) pick the piece O
The move from me is e
Number of total SOSs created so far: 14
Number of SOSs created by me so far: 10

    . . . S . O      0 1 2 3 4 5
    O . S S O .      6 7 8 9 a b
    . . O O . S      c d e f g h
    . S S S S S      i j k l m n
    S . O O O .      o p q r s t
    S O S S S S      u v w x y z

Hit the spacebar to start the System’s next move.
 
My turn.  I (System) pick the piece S
The move from me is b
Number of total SOSs created so far: 15
Number of SOSs created by me so far: 11

    . . . S . O      0 1 2 3 4 5
    O . S S O S      6 7 8 9 a b
    . . O O . S      c d e f g h
    . S S S S S      i j k l m n
    S . O O O .      o p q r s t
    S O S S S S      u v w x y z

Hit the spacebar to start the System’s next move.
 
My turn.  I (System) pick the piece O
The move from me is g
Number of total SOSs created so far: 17
Number of SOSs created by me so far: 13

    . . . S . O      0 1 2 3 4 5
    O . S S O S      6 7 8 9 a b
    . . O O O S      c d e f g h
    . S S S S S      i j k l m n
    S . O O O .      o p q r s t
    S O S S S S      u v w x y z

Hit the spacebar to start the System’s next move.
 
My turn.  I (System) pick the piece S
The move from me is 7
Number of total SOSs created so far: 18
Number of SOSs created by me so far: 14

    . . . S . O      0 1 2 3 4 5
    O S S S O S      6 7 8 9 a b
    . . O O O S      c d e f g h
    . S S S S S      i j k l m n
    S . O O O .      o p q r s t
    S O S S S S      u v w x y z

Hit the spacebar to start the System’s next move.
 
My turn.  I (System) pick the piece O
The move from me is t
Number of total SOSs created so far: 19
Number of SOSs created by me so far: 15

    . . . S . O      0 1 2 3 4 5
    O S S S O S      6 7 8 9 a b
    . . O O O S      c d e f g h
    . S S S S S      i j k l m n
    S . O O O O      o p q r s t
    S O S S S S      u v w x y z

Hit the spacebar to start the System’s next move.
 
My turn.  I (System) pick the piece O
The move from me is p
Number of total SOSs created so far: 20
Number of SOSs created by me so far: 16

    . . . S . O      0 1 2 3 4 5
    O S S S O S      6 7 8 9 a b
    . . O O O S      c d e f g h
    . S S S S S      i j k l m n
    S O O O O O      o p q r s t
    S O S S S S      u v w x y z

Hit the spacebar to start the System’s next move.
 
My turn.  I (System) pick the piece S
The move from me is i
Number of total SOSs created so far: 21
Number of SOSs created by me so far: 17

    . . . S . O      0 1 2 3 4 5
    O S S S O S      6 7 8 9 a b
    . . O O O S      c d e f g h
    S S S S S S      i j k l m n
    S O O O O O      o p q r s t
    S O S S S S      u v w x y z

Hit the spacebar to start the System’s next move.
  
My turn.  I (System) pick the piece O
The move from me is d
Number of total SOSs created so far: 23
Number of SOSs created by me so far: 19

    . . . S . O      0 1 2 3 4 5
    O S S S O S      6 7 8 9 a b
    . O O O O S      c d e f g h
    S S S S S S      i j k l m n
    S O O O O O      o p q r s t
    S O S S S S      u v w x y z

Hit the spacebar to start the System’s next move.
  
My turn.  I (System) pick the piece S
The move from me is 0
Number of total SOSs created so far: 23
Number of SOSs created by me so far: 19

    S . . S . O      0 1 2 3 4 5
    O S S S O S      6 7 8 9 a b
    . O O O O S      c d e f g h
    S S S S S S      i j k l m n
    S O O O O O      o p q r s t
    S O S S S S      u v w x y z

Continue? (y/n)  y 
Your turn.  You (User) pick a piece: (S|O)  S 
Enter your next move: (0..z)  c 
Number of total SOSs created so far: 24
Number of SOSs created by you so far: 5

    S . . S . O      0 1 2 3 4 5
    O S S S O S      6 7 8 9 a b
    S O O O O S      c d e f g h
    S S S S S S      i j k l m n
    S O O O O O      o p q r s t
    S O S S S S      u v w x y z

Continue? (y/n)  y 
Your turn.  You (User) pick a piece: (S|O)  O 
Enter your next move: [0..z]  4 
Number of total SOSs created so far: 24
Number of SOSs created by you so far: 5

    S . . S O O      0 1 2 3 4 5
    O S S S O S      6 7 8 9 a b
    S O O O O S      c d e f g h
    S S S S S S      i j k l m n
    S O O O O O      o p q r s t
    S O S S S S      u v w x y z

Hit the spacebar to start the System’s next move.
  
My turn.  I (System) pick the piece S
The move from me is 2
Number of total SOSs created so far: 24
Number of SOSs created by me so far: 19

    S . S S O O      0 1 2 3 4 5
    O S S S O S      6 7 8 9 a b
    S O O O O S      c d e f g h
    S S S S S S      i j k l m n
    S O O O O O      o p q r s t
    S O S S S S      u v w x y z

Continue? (y/n)  y 
Your turn.  You (User) pick a piece: (S|O)  O 
Enter your next move: (0..z)  1 
Number of total SOSs created so far: 25
Number of SOSs created by you so far: 6

    S O S S O O      0 1 2 3 4 5
    O S S S O S      6 7 8 9 a b
    S O O O O S      c d e f g h
    S S S S S S      i j k l m n
    S O O O O O      o p q r s t
    S O S S S S      u v w x y z

I (System) won!  I have 19 SOSs and you have 6 SOSs.
New game? (y/n)  n 

-- program is finished running --

Possible Instructions to Be Used
The following directives and instructions may be used in this exercise, but you are not limited to them. For instruction syntax, check MIPS Instruction Reference.

No.	Directive	Description
1	`.ascii` `"string"`	Allocating space for string
2	`.asciiz` `"string"`	Allocating space for string, NULL terminated
3	`.byte`	Allocating space for a byte
4	`.data`	Beginning of data section
5	`.globl` `name`	Making the following name be a global symbol
6	`.half`	Allocating space for a half word (two bytes)
7	`.space` `n`	Allocating `n` bytes of space
8	`.text`	Beginning of text section
No.	Instruction	Operation	Description
1	`add` `rd, rs, rt`	`rd = rs + rt`	Add; `rd`: destination register, `rs`: first source register, and `rt`: second source register or immediate value. Check MIPS Registers and Usage Convention.
2	`addu` `rd, rs, rt`	`rd = rs + rt` (no overflow)	Add unsigned
3	`beq` `rs, rt, label`	`if rs==rt then goto label`	Branch if equal to
4	`beqz` `rs, label`	`if rs==0 then goto label`	Branch if equal to zero
5	`bgez` `rs label`	`if rs≥0 then goto label`	Branch if greater than or equal to zero
6	`bgt` `rs, rt, label`	`if rs>rt then goto label`	Branch if greater than
7	`ble` `rs, rt, label`	`if rs≤rt then goto label`	Branch if less than or equal to
8	`blt` `rs, rt, label`	`if rs<rt then goto label`	Branch if less than
9	`bne` `rs, rt, label`	`if rs≠rt then goto label`	Branch if not equal to
10	`bnez` `rs, label`	`if rs≠0 then goto label`	Branch if not equal to zero
11	`j` `label`	`jump to label`	Jump
12	`jal` `label`	`jump to label` and save the return address in `$31` or `$ra`	Jump and link
13	`jr` `rs`	`jump to [rs]`; [ ]: contents of	Jump and link
14	`la` `rd, mem`	`rd = address( mem )`	Load address
15	`lb` `rd, mem`	`rd = mem`	Load byte
16	`lh` `rd, mem`	`rd = mem`	Load half word
17	`li` `rd, imm`	`rd = imm`	Load immediate
18	`lw` `rd, mem`	`rd = mem`	Load word
19	`move` `rd, rs`	`rd = rs`	Move register
20	`mul` `rd, rs, rt`	`rd = rs × rt`	Multiply
21	`sb` `rs, mem`	`mem = rs`	Store byte
22	`sub` `rd, rs, rt`	`rd = rs - rt`	Subtract
23	`subu` `rd, rs, rt`	`rd = rs - rt` (no overflow)	Subtract unsigned
24	`sw` `rs, mem`	`mem = rs`	Store word
25	`syscall`		System call; check System Services.
26	`xor` `rd, rs, rt`	`rd = rs xor rt`	Bitwise exclusive or

The following table lists some System Services provided by the MARS:

Service	Code in `$v0`	Arguments	Result
print_int	1	`$a0` = integer to be printed
print_float	2	`$f12` = float to be printed
print_double	3	`$f12` = double to be printed
print_string	4	`$a0` = address of string in memory
read_int	5		integer returned in `$v0`
read_float	6		float returned in `$v0`
read_double	7		double returned in `$v0`
read_string	8	`$a0` = address of string input buffer `$a1` = length of string buffer (`n`)
malloc	9	`$a0` = amount	address in `$v0`
exit	10
print character	11	`$a0` = character to be printed
read character	12		character returned in `$v0`
random int range	42	`$a0` = i.d. of pseudorandom number generator (any int). `$a1` = upper bound of range of returned values.	`$a0` contains pseudorandom, uniformly distributed int value in the range 0 ≤ [int] < [upper bound], drawn from this random number generator’s sequence.

Evaluations
The following features will be considered when grading:

Specifications:
- The instructor has given the exercise specifications as detailedly as possible. If you are confused about the specifications, you should ask in advance. Study the specifications very carefully. No excuses for misunderstanding or missing parts of the specifications after grading.
- The specifications may not be possible to cover every detail. You are free to implement the issues not mentioned in the specifications, but the implementations should make sense. Implemented functions lacking common sense may cause the instructor to grade your exercise mistakenly, and thus lower your grade.
- The exercise must meet the specifications. However, exercises with functions exceeding the specifications will not receive extra credits.

Grading:
- This exercise will be graded after the source code is submitted. Students take full responsibility if the code does not work.
- The MARS simulator will be used to grade exercises. Make sure your exercise works on MARS.
- Before submitting the exercise, test it comprehensively. Absolutely no extra points will be granted after grading.
- A set of test data will be used to test the exercises of all students. The grades are primarily based on the results of testing. Other factors such as performance, programming styles, algorithms, and data structures will be only considered minimally.
- Unless specified, no error checking is required.
- The total weight of exercises is 20% (10% each) of the final grade.
- Though Exercise II covers parts of Exercise I, you still have to submit both exercises separately. One exercise will not be counted twice.
- The instructor will inform you the exercise evaluations by emails or Blackboard after grading.

Comments:
- According to a study, students in computer-science courses learn much more by building medium/large-scale exercises instead of many small-scale test programs, which give fragmented knowledge contrary to solid understanding of the language.
- Time management is critical for software development. If you are not able to complete the exercises, show whatever you have accomplished, so the instructor can give partial credit to your exercises.