C++ OOP: output issue

Question

I have one header file and a source file. I have declared my variables in header file and I am trying to implement them in my source file.
I am trying to add the to values of variable a and b but the output is 0 for some reason.
Any idea as why is 0 the output even though I am trying to return a + b.

my header file (sum.h) code is below:

class sum {
private:
int a;
int b;

public:
int add_numbers();
int setValues(int a, int b);
};

my source file is code is below ( .cpp)

#include <iostream>
#include "sum.h"
using namespace std;

int sum::add_numbers() {
return a + b;
}

int setValues( int a = 6, int b = 8);

int main() {
sum test;
cout << test.add_numbers()<<endl;
return 0;
}

Answer 1

To make things easier, I think you can make a parametric constructor that accepts values for <a> and <b>.

This way you can setup <a> and <b> as the object is constructed, rather than having to call setValues() before calling add_numbers().

If you want to use sum::setValues() then you should define it in source file cause it doesn't seem to be defined in there. You have this line ...

int setValues( int a = 6, int b = 8 );

Which is a forward declaration of a free function, not a member of class `sum`. It should've been something like ...

int sum::setValues( int a = 6, int b = 8 )
{
// code here ...
}

But even with this, you'd still have to call setValues() before add_numbers() - in order for <a> and <b> to be properly initialized.

That was why I suggest you to make a parametric constructor instead. I also think that setValues() return type should be defined as `void` because it's a setter. Unless you want the return value to represent a status, whether the given arguments were valid, or not.

Answer 2

Humza Ali you did not define setValues.

#include <iostream>
using namespace std;

class Sum {
private:
int a;
int b;
public:
void setValues(int x, int y);
int add_numbers();
};

int Sum::add_numbers() {
return a + b;
}

void Sum::setValues(int x, int y) {
a = x;
b = y;
}

int main() {
Sum test;
test.setValues(6, 8);
cout << test.add_numbers()<<endl;
}