Explain tha code and find the output?

Question

#include <stdio.h>
#define fun(x,y)(x>y)?(x*y):(y-x);
int main() {
int p=7,q=6,r=4;
r+=fun(++p,q++);
printf("%d%d%d",p,q,r);
return 0;
}

Answer 1

Since the macro is just a text replacement, the line

r += fun( ++p, q++ );

becomes

r += ( ++p > q++ ) ? ( ++p * q++ ) : ( q++ - ++p );

after the preprocessor is finished.
Substituting the values shows that

8 > 6

is true, hence the first part of the ternary operator is executed, which evaluates to 9 * 7 = 63.
Therefore, at the end you get p = 9, q = 8 and r = 67.

If you want to confirm the output, just paste the code into the playground and try it yourself.