How to write a function which returns complex in C++?

I am trying to do numerical calculations with C++. Here is the sample code

#include <complex> 
using namespace std;


complex<double> complexDo(float a, float b){

    return (a+b,a-b);
}

int main(){

    cout << "complexDo="<<complexDo(3,2) <<'\n';
    return 0;
}

The terminal will show after compiling

complexDo=(1,0)

But I expect to appear like (5, 1), and what is the problem here? Or this way of writing is not valid in C++?

>Solution :

The expression (a+b,a-b) is equivalent to (a-b) because it’s just a parenthesized use of the common comma expression.

To create an object you must use curly-braces {} as in

return {a+b,a-b};