How to edit ELF files in Linux?

Question

I have written two similar C programs. How can I make the outputs of both code same by editing one of the ELF files not the actual code?

/**
* prg1.c
*/
#include <stdio.h>
#include <stdlib.h>
int main()
{
        int a = 5;
        int b = 10;
        int sum;
        sum = a + b;
        printf("sum is %d\n", sum);
        return(0);
}
/**
* prg2.c
*/
#include <stdio.h>
#include <stdlib.h>
int main()
{
        int a = 5;
        int b = 20;
        int sum;
        sum = a + b;
        printf("sum is %d\n", sum);
        return(0);
}

Answer 1

In your second program's elf file find the occurrence of 20 and change it to 10.

To do that you can do something like this - Find 14 (hex of 20) in your elf file and change it to A and making sure length is same by adding extra 0. To do this you can use any elf editor, I use 'Hex Fiend' for mac.