Can someone explain me this code

Question

What is the output of this code?
#define prod(i, j) i * j
int main() {
int x = 3, y = 4;
printf("%d", prod(x + 2, y - 1));
return 0;
}

Answer 1

Macros in C simply replace text. That's all they do. So if we call the macro defined in your code like this
prod(2, 3)
It will simply be replaced by 2*3 in the main code. In the same way, if call the macro like this
prod(2 + 3, 4 - 2)
It will simply be changed to '2 + 3 * 4 - 2'. So now, according to operator precedence '2 + 3 * 4 - 2' is 12, when actually (2+3) * (4-2) is 10.

Same way in your code,
printf("%d", prod(x + 2, y - 1));
will be changed to
printf("%d", x + 2 * y - 1);
Now according to operator precdence
x + 2 * y - 1
= 3 + 2 * 4 - 1
= 3 + 8 - 1
= 10
So 10 is printed

Answer 2

Yes. C/C++ macros basically replace text in your program. But using paranthesis around expressions passed as macro arguments can fix this problem atleast. For example
printf("%d", prod( (x + 2), (y - 1)));
here, prod( (x + 2), (y - 1) ) will change to
(x + 2) * (y - 1)
= (3 + 2) * (4 - 1)
= 5 * 3
= 15

Answer 3

Is that only way for using macros?

Answer 4

Stupid question, but how can I say marcos in other word. What is the synonymous? 😅

Answer 5

I don't know any synonym of macro. But what is the problem in using 'macro'? I mean, why do you want a synonym of it?

Answer 6

Because i'm always think about the macros in Microsoft access and I'm not sure that is the same thing. That's why.

Answer 7

Cлaвeн Ђервида I haven't worked with Microsoft access/excel macros much but as far as I know, they record whatever operations you're doing and when they are called they repeat the operations. So I think it makes sense to say that they are just like macros in programming languages.

Same as macros in microsoft access/excel, you can list a few statements in a C macro which you want to execute when the macro is called. For example, the following macro takes 4 arguments and constructs a single statement for loop that loops from start till end

#define frange(start, stop, step, operation) for (int _ = start; _ < stop; _ += step) operation

when you call frange in your code, it will become a for loop
int sum = 0;
frange(0, 10, 1, sum += 1);
printf("sum %d", sum);