Where do you typically declare and define functions outside a class in c++?

Question

I've been studying C++ for a little while now and want to start getting into actual application/software development. The problem is I'm having a hard time figuring out some of the more practical aspects of how to exactly setup a project. My question today is if I have a function that is not being declared and defined in a standard class structure, where exactly should I, or is it most common to, declare and define it? Most tutorials you watch will declare a function in main.cpp, above main() and then define it below main() but I assume that is just for teaching purposes and not real world application. Should you just create function header and source files just as you would with classes?

Answer 1

You will need to declare (prototype) the function in a .h file, and then implement it in a .cpp file. Example:

main.cpp:

#include "header.h"
int main()
{
    // use the functions
    printf("%f, %f", add(10, 10), sub(64, 2.8));
}

header.h:

double add(double, double);       // function declarations
double sub(double, double);

header.cpp:

#include "header.h"
double add(double a, double b)    // function implementations
{
    return a + b;
}
double sub(double a, double b)
{
    return a - b;
}

Answer 2

Yes, you can have the main cpp file along with separate header/source files for your own functions. Something like this:

/main.cpp

#include "myFunctions.h"

int main(){

    printSum(5, 5);
    return 0;    
}

/myFunctions.h

#ifndef MYFUNCTIONS_H
#define MYFUNCTIONS_H

void printSum(int, int);

#endif

/myFunctions.cpp

#include "myFunctions.h"

void printSum(int num1, int num2){

    cout << num1 + num2 << "\n"

}