Self- Doubt

Question

#include<stdio.h>
int main()
{
    int i= 0;
    int j= ++i + i++;
    printf("%d\n",j)
}

I think output is $2$ but output is $3$. How is it possible?

pls explain.......

Answer 1

It is "undefined behaviour of C". Different compilers will give different outputs. Please refer:

1. https://www.geeksforgeeks.org/undefined-behavior-c-cpp/

2. https://www.geeksforgeeks.org/sequence-points-in-c-set-1/

Comments

I don't know about other compiler but gcc compiler give output 3.

---

To get out of sequence problem(or undefined behaviour) modern compilers try to use either stack or registers to evaluate a same variable. Depending on which compiler is using which approach (stack or registers), you will get a different answer. But none of them is correct because C's developers did not define behaviour for such operations on a single variable and thus called undefined behaviour. Go through the links I gave, you will understand it.

Answer 2

output are depend on the compiler but i you run this code in standard turbo c compiler then i will give output as 2