Having some problem with a GCF program

So, I am new to C++ and only just started. I have bought a book called C++ Without Fear by Brian Overland, and I am having a problem with one of the exercises to do with the Greatest Common Factor.

The source code is:

Code:

#include <iostream>
using namespace std;

int gcf(int a, int b);

int main() {
    int a = 0, b = 0;
    while(1) {
        cout << "Enter a number (0 to quit): ";
        cin >> a;
        if (a==0)
        break;
        cout << "Enter 2nd number: ";
        cin >> b;
        cout << "GCF = " << gcf(a, b) << endl;
    }
    return 0;
}

int gcf(int a, int b) {
    if (a % b == 0)
    return b;
    else
    return gcf(b, a % b);
    cout << gcf(b, a % b);
}

That much I have managed to understand, but now after he explains it, he says to do an exercise where I revise the program so it shows all the steps involved in the algorithm.

For example-
GCF(300, 500) =>
GCF(500, 300) =>
GCF(300, 200) =>
GCF(200, 100) =>
GCF = 100

Right now, all that the code does is immediately give the answer.
Please help me out.

Thanks!

The cout in your gcf() function is unreachable.
One way or another, it hits a return before then.

Put it at the start, and just print a,b

Thanks, working fine now