CODEWITHSUNDEEP
carraysincrement
Maciej Tarach
Maciej Tarach

Reputation: 23

Tricky array increment in C

I do not understand why before if-statement ++b[1] is equal to 1, but after if-statment ++b[1] is equal to 0. Why ++b[1] does not increase inside if-statement?

#include <stdio.h>

int main()
{
    int c = 0;
    int b[3] = {4};
    printf("%d\n", ++b[1]); // return 1
    b[1]--;
    if((c-- && ++b[1])|| b[0]++)
    {
        printf("%d\n", b[1]); // return 0
        printf("%d\n", c); // return -1
    }
    return 0;
}

Upvotes: 2

Views: 132

Answers (2)

miradulo
miradulo

Reputation: 29690

There's just some confusing operator usage going on here.

  • c-- is a postfix decrement, and so in the conditional statement c is evaluated as false (as it is 0), before being decremented.
  • Now since && short circuits and only evaluates the second condition if the first is true, we do not evaluate ++b[1], but enter the conditional on the truthiness of b[0]++.

Upvotes: 2

rom1v
rom1v

Reputation: 2969

if((c-- && ++b[1])|| b[0]++)

c-- yields 0, so ++b[1] is not evaluated.

This is called short-circuit evaluation.

Upvotes: 3

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