While loop in MIPS (Beginner in MIPS)

Question

I am trying to write a program to calculate nCr where n and r are input by the user. My approach is following:

1. I ask to user to enter value of n.

2. Then I ask the user to enter value of r.

3. Then I calculate value of n-r.

4. Then using three while loops I calculate the value of n! r! and (n-r)!

5. Then I divide by n! by r! and (n-r)!

6. Then I display it to the user.

7. Following is my code:

   .data 
        prompt1: .asciiz "Enter the value of n:\n"
        prompt2: .asciiz "Enter the value of r:\n"
        message: .asciiz "The value of nCr is: "
   
    .text
         #Prompt the user to enter value of n
         li $v0,4
         la $a0,prompt1
         syscall
   
         #Get the value of n
         li $v0,5
         syscall
   
         #Store the value of n in $t0
         move $t0,$v0
   
         #Prompt the user to enter value of r
         li $v0,4
         la $a0,prompt1
         syscall
   
         #Get the value of r
         li $v0,5
         syscall
   
         #Store the value of r in $t2
   
   
         move $t2,$v0
   
         #Getting the value of (n-r)
         sub $t4,$t0,$t2
   
         #Calculating value of n!
         addi $t1,$zero,1
   
         while:
               blt $t0,1,exit
               mul $t1,$t1,$t0
               sub $t0,$t0,1
               j while
         exit:
               li $v0,10
               syscall
   
        #Calculating the value of r!
        addi $t3,$zero,1
   
        while:
              blt $t2,1,exit
              mul $t3,$t3,$t2
              sub $t2,$t2,1
              j while
   
         exit:
              li $v0,10
              syscall
   
        #Calculating the value of (n-r)!
        addi $t5,$zero,1
   
        while:
              blt $t4,1,exit
              mul $t5,$t5,$t4
              sub $t4,$t4,1
              j while
   
       exit:
             li $v0,10
             syscall
   
       #Getting the final value
       div $s0,$t1,$t3
       div $s1,$s0,$t5
   
       #Displaying the message
       li $v0,4
       la $a0,message
       syscall
   
       #Display the answer
       addi $a0,$s1,0
       syscall
   

The Error which I am getting is this:

1. line 46 column 6: label "while" already defined.
2. line 46 column 6: label "exit" already defined.

What I am doing wrong here? Is it not the correct way to use three while loops in a mips

Answer 1

If you write while: in your program, you are creating a label named while, which is an alias for the line number where you place it. Within one file, you can only create one label with a certain name.

A solution for your problem would be to name the labels while1, while2 and while3. Same holds for your exit labels.