Question

im trying to complete mips program code about a calculator program that can calculate integer addition / subtraction written using the MIPS assembler. im having hard times to debug this. The input is given to the array of Formula char (base address $ s0) in the form of a formula. The null character (\ 0, ASCII code 0) is placed at the end. The calculation result is given to the register $ s1 and the overflow is ignored. For example, if the input is Formula = “100 + 20 + 3”, $ s1 = 123, and if Formula = “− 100 + 20-3”, $ s1 = −83 is output. The '+' and-in the program are the characters + 'and-, in ASCII respectively, and the ASCII characters are 0..9 are 48 (10), 49 (10) and 57 (10).

    .text
    .globl main
  
            main:
            la $s0,word ##copy base address of array to t1
           add $s1, $zero, $zero
            add $s2, $zero, $zero
            Addi $s3,$zero,1
            Addi $t1, $zero,'+'
            Addi $t2,$zero,'-'
            addi $t3,$zero,10
  
            Loop: lb $t0,0($s0)
            Addiu $s0,$s0,1
            Beq $t0,$t1,Plus
            Beq $t0,$t2,Minus
            Beq $t0,$zero,Cal
            Addi $t0,$t0,-48
            Mul $s2, $s2, $t3
            Add $s2,$s2,$t0
            J Loop
  
            End:
          
  
  
    li $v0,1
    move $a0,$s1
    syscall
            li $v0, 10
    syscall
  
              Plus: addi $s4, $zero, 1
              j Cal
              Minus: addi $s4, $zero, 0
              Cal: beq $s3,$zero,Subn
              Addn:
            
              add $s1,$s1,$s2　//here im not sure
           
              beq $s4,1,Join
            
              Subn: sub $s2,$s1,$s2
              Join : add $s2,$zero,$zero
              Beq $t0,$zero,End
               Add $s3,$s4,$zero
               J Loop
  
  
    Exit:
    li $v0, 10
    syscall
  
    .data
    word: .asciiz "-100+20+3"
    result: .asciiz "$s1->"
    prompt: .asciiz "$s0->"

it produce 23 but the right answer -83, which one is wrong?

However when debugging this code produce 23, but the correct result is -83 where is the wrong part?

Answer 1

Please find the updated code below::

.text
.globl main
  
main:
la $s0,word ##copy base address of array to t1
add $s1, $zero, $zero
add $s2, $zero, $zero
Addi $s3,$zero,1
Addi $t1, $zero,'+'
move $s7,$t1
Addi $t2,$zero,'-'
addi $t3,$zero,10
  
Loop: lb $t0,0($s0)
Addiu $s0,$s0,1
Beq $t0,$t1,Plus
Beq $t0,$t2,Minus
Beq $t0,$zero,End
Addi $t0,$t0,-48
Mul $s2, $s2, $t3
Add $s2,$s2,$t0
J Loop
  
  
  
End:
   li $s6,1
Beq $s7,$t1,Addn
Beq $s7,$t2,Subn  
  
  
  
li $v0, 10
syscall
  
Plus:
move $s4,$t1 #store plus sign
    Beq $s7,$t1,Addn
Beq $s7,$t2,Subn
  
j Join
Minus:
move $s4,$t2 #store plus sign
    Beq $s7,$t1,Addn
Beq $s7,$t2,Subn
   j Join

Addn:
add $s1,$s1,$s2 #here im not sure
j Join
Subn: sub $s1,$s1,$s2
  
Join :
beq $s6,1,Exit
move $s7,$s4 #load value
add $s2,$zero,$zero
Beq $t0,$zero,End
Add $s3,$s4,$zero
J Loop
  
  
Exit:
li $v0,1
move $a0,$s1
syscall
  
.data
word: .asciiz "-100+20+3"
result: .asciiz "$s1->"
prompt: .asciiz "$s0->"

output: