CODEWITHSUNDEEP
for-loopmips
the_answer_is_xyz
the_answer_is_xyz

Reputation: 521

Calculate the sum of all odd number from 1 to 10 with for loop in MIPS

I'm writing an MIPS program using for-loop to calculate the sum of all odd number from 1 to 10. It should be 25, yet I got 48. I don't know where is the error. Here's my code:

################# Pseudocode ##################### 
 i = 1
 n = 10
 sum = 0
   for(i=1; i<=10; i+=2) {
       sum += i;
   }
  printf("The sum of all odd number from 1 to 10 is: %d", sum);
  return 0;

################# Data segment ##################### 
        .data
msg:    .asciiz     "\ncurrent tally: \n"

################# Code segment ##################### 
    .text
    .globl  main

main:
    li      $t0, 1      # temp counter, starts at 1 
    li      $t1, 0      # set to zero, to store sum

add_loop:
    bgt    $t0, 11, end_loop    # break out of loop if counter > 11
    addi    $t0, $t0, 2          # add 2 in $t0 to skip even num
    add     $t1, $t1, $t0        # sum += i

    li      $v0, 4
    la      $a0, msg
    syscall                      # print out user-friendly msg

    li      $v0, 1
    move    $a0, $t1
    syscall                      # print out result from loop

    j       add_loop

end_loop:
    li      $v0, 10              # terminate program run and
    syscall                      # exit

The output: current tally: 3 current tally: 8 current tally: 15 current tally: 24 current tally: 35 current tally: 48 -- program is finished running --

Upvotes: 1

Views: 2719

Answers (1)

b-fg
b-fg

Reputation: 4137

You start your t0 var with 1 and then you add 2 before add $t1, $t1, $t0, hence the first value to be summed to t1 is 3 and you are missing 1.

Then also since the break condition is >11, 11 is also summed to t1. Finally, you are adding +13 somewhere else as well (maybe it makes a last iteration before breaking the loop?), so -1+11+13 gives you the 23 of difference between 25 and 48.

So probably would be better to do

add_loop:
    bgt    $t0, 9, end_loop    # break out of loop if counter > 9 (so 9 is counted as well!)
    add     $t1, $t1, $t0        # sum += i
    addi    $t0, $t0, 2          # add 2 in $t0 to skip even num

Since you already start with t0=1

Upvotes: 2

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