c preprocessor - C #define macros

Question

Here is what i have and I wonder how this works and what it actually does.

#define NUM 5
#define FTIMES(x)(x*5)

int main(void) {
    int j = 1;
    printf("%d %d
", FTIMES(j+5), FTIMES((j+5)));
}

It produces two integers: 26 and 30.

How does it do that?

Answer 1

The reason this happens is because your macro expands the print to:

printf("%d %d
", j+5*5, (j+5)*5);

Meaning:

1+5*5 and (1+5)*5