Question

I saw this below code in an website.
I could not able to understsnd how the result is coming as 11, instead of 25 or 13.

Why I am thinking 25 because SQ(5) 5*5

or 13 because

SQ(2) = 4;

SQ(3) = 9;

may be final result will be 13 (9 + 4)
But surprised to see result as 11.
How the result is coming as 11?

using namespace std;
#define SQ(a) (a*a)
int main()
{
    int ans = SQ(2 + 3);
    cout << ans << endl;
system("pause");
}

Answer 1

#define expansions kick in before the compiler sees the source code. That is why they are called pre-processor directives, the processor here is the compiler that translates C to machine readable code.

So, this is what the macro pre-processor is passing on to the compiler:

SQ(2 + 3) is expanded as (2 + 3*2 + 3)

So, this is really 2 + 6 + 3 = 11.

How can you make it do what you expect?

1. Enforce the order of evaluation. Use (), either in the macro definition or in the macro call.
   OR
2. Write a simple function that does the job