Variables combined with && and ||

Question

What do the last lines mean?

a=0;
b=0;
c=0;

a && b++;
c || b--;

Can you vary this question to explain with more interesting example?

Answer 1

For the example you gave: if a is nonzero, increment b; If c is zero, decrement b.

Due to the rules of short-circuiting evaluation, that is.

You could also test this out with a function as the right-hand-side argument; printf will be good for this since it gives us easily observable output.

#include <stdio.h>
int main()
{
    if (0 && printf("RHS of 0-and\n"))
    {
    }

    if (1 && printf("RHS of 1-and\n"))
    {
    }

    if (0 || printf("RHS of 0-or\n"))
    {
    }

    if (1 || printf("RHS of 1-or\n"))
    {
    }

    return 0;
}

Output:

RHS of 1-and
RHS of 0-or

Answer 2

a && b++;    is equivalent to:  if(a) b++;

c || b--;    is equivalent to:   if(!c) b--;

but there is no point to writing these kind of expression. It doesn't compile to better code and is less readable in almost all cases even if it looks shorter.