How exactly does the ?: operator work in C?

Question

I have a question, how the compiler operate on the following code:

#include<stdio.h>

int main(void)
{
  int b=12, c=11;
  int d = (b == c++) ? (c+1) : (c-1);
  printf("d = %i\n", d);
}

I am not sure why the result is ‍‍‍d = 11.

Answer 1

In int d = (b == c++) ? (c+1) : (c-1);:

• The value of c++ is the current value of c, 11. Separately, c is incremented to 12.
• b == 11 is false, since b is 12.
• Since (b == c++) is false, (c-1) is used. Also, the increment of c to 12 must be completed by this point.
• Since c is 12, c-1 is 11.
• d is initialized to that value, 11.