Question

Step 2. Write a C function to passed two numbers to the function and calculate the sum of all the numbers between them (both inclusive). [50 marks]

a. Make a version with for loop
b. Make a version with while loop

c. Make a version with do.. while loop d. Make a version with goto loop

Tip : Try to use the same number of variables and almost the same logic in all the four loops

To do:
Using the command

$gcc -O1 -S filename.c

Will generate the assembly version of the loop. Now you need to analyze and compare them. Are these codes same or different? If different, identify the differences

Answer 1

//c code for a:

#include <stdio.h>

int sum_for(int a,int b)
{
int i,sum=0;
for(i=a;i<=b;i++)
{
    sum += i;
}
return sum;
}
int main(void) {
int a=1,b=5;
int sum;
sum = sum_for(a,b);
printf("%d ",sum);
return 0;
}

//output for a:

//code for b:

#include <stdio.h>

int sum_while(int a,int b)
{
int i=a,sum=0;
while(i>b)
{
    sum += i;
    i++;
}
return sum;
}
int main(void) {
int a=1,b=5;
int sum;
sum = sum_while(a,b);
printf("%d ",sum);
return 0;
}

//Output for b:

//code for c:

#include <stdio.h>

int sum_dowhile(int a,int b)
{
int i=a,sum=0;
do
{
    sum += i;
    i++;
}while(i<=b);
return sum;
}
int main(void) {
int a=1,b=5;
int sum;
sum = sum_dowhile(a,b);
printf("%d ",sum);
return 0;
}

//output for c:

//After issuing the command gcc -O1 -S sum_for.c
gcc -O1 -S sum_while.c
gcc -O1 -S sum_dowhile.c

we can see three corresponding assembly language codes(sum_for.s,sum_while.s,sum_dowhile.s) created in the same directory

#NOTE: The assembly codes are automatically generated by system.If not check the answer last part for those system generated assembly codes.

Comparisons:

As we can see in line 9, line 15 for both the codes. for loop uses termination condition jump to terminate-loop if i is greater than given value, for the looping condition it uses jump to loop if i is less than or equals to b.
where as while loop uses termination condition jump to terminate-loop is i is less than given values,in looping condition it uses jump to loop if i is less than given values.

dowhile uses looping condition in line 13, i.e go through the loop if i is less than or equal to given values.

//Assrmbly code for A: sum_for.s

    .file   "sum_for.c"
   .text
   .globl   sum_for
   .type   sum_for, @function
sum_for:
.LFB23:
   .cfi_startproc
   cmpl   %esi, %edi
   jg   .L4
   movl   $0, %eax
.L3:
   addl   %edi, %eax
   addl   $1, %edi
   cmpl   %edi, %esi
   jge   .L3
   rep ret
.L4:
   movl   $0, %eax
   ret
   .cfi_endproc
.LFE23:
   .size   sum_for, .-sum_for
   .section   .rodata.str1.1,"aMS",@progbits,1
.LC0:
   .string   "%d "
   .text
   .globl   main
   .type   main, @function
main:
.LFB24:
   .cfi_startproc
   subq   $8, %rsp
   .cfi_def_cfa_offset 16
   movl   $15, %edx
   movl   $.LC0, %esi
   movl   $1, %edi
   movl   $0, %eax
   call   __printf_chk
   movl   $0, %eax
   addq   $8, %rsp
   .cfi_def_cfa_offset 8
   ret
   .cfi_endproc
.LFE24:
   .size   main, .-main
   .ident   "GCC: (Ubuntu 5.4.0-6ubuntu1~16.04.12) 5.4.0 20160609"
   .section   .note.GNU-stack,"",@progbits

//assembly code for B: sum_while.s

    .file   "sum_while.c"
   .text
   .globl   sum_while
   .type   sum_while, @function
sum_while:
.LFB23:
   .cfi_startproc
   cmpl   %esi, %edi
   jle   .L4
   movl   $0, %eax
.L3:
   addl   %edi, %eax
   addl   $1, %edi
   cmpl   %edi, %esi
   jl   .L3
   rep ret
.L4:
   movl   $0, %eax
   ret
   .cfi_endproc
.LFE23:
   .size   sum_while, .-sum_while
   .section   .rodata.str1.1,"aMS",@progbits,1
.LC0:
   .string   "%d "
   .text
   .globl   main
   .type   main, @function
main:
.LFB24:
   .cfi_startproc
   subq   $8, %rsp
   .cfi_def_cfa_offset 16
   movl   $0, %edx
   movl   $.LC0, %esi
   movl   $1, %edi
   movl   $0, %eax
   call   __printf_chk
   movl   $0, %eax
   addq   $8, %rsp
   .cfi_def_cfa_offset 8
   ret
   .cfi_endproc
.LFE24:
   .size   main, .-main
   .ident   "GCC: (Ubuntu 5.4.0-6ubuntu1~16.04.12) 5.4.0 20160609"
   .section   .note.GNU-stack,"",@progbits

//assembly code for C: sum_dowhile.s

    .file   "sum_dowhile.c"
   .text
   .globl   sum_dowhile
   .type   sum_dowhile, @function
sum_dowhile:
.LFB23:
   .cfi_startproc
   movl   $0, %eax
.L2:
   addl   %edi, %eax
   addl   $1, %edi
   cmpl   %esi, %edi
   jle   .L2
   rep ret
   .cfi_endproc
.LFE23:
   .size   sum_dowhile, .-sum_dowhile
   .section   .rodata.str1.1,"aMS",@progbits,1
.LC0:
   .string   "%d "
   .text
   .globl   main
   .type   main, @function
main:
.LFB24:
   .cfi_startproc
   subq   $8, %rsp
   .cfi_def_cfa_offset 16
   movl   $15, %edx
   movl   $.LC0, %esi
   movl   $1, %edi
   movl   $0, %eax
   call   __printf_chk
   movl   $0, %eax
   addq   $8, %rsp
   .cfi_def_cfa_offset 8
   ret
   .cfi_endproc
.LFE24:
   .size   main, .-main
   .ident   "GCC: (Ubuntu 5.4.0-6ubuntu1~16.04.12) 5.4.0 20160609"
   .section   .note.GNU-stack,"",@progbits