Functions

Relax. We'll talk through this in plain words — no textbook voice.

A function is a block of code you name and write separately to handle one task. It makes code reusable, keeps your program easier to read, and makes bugs easier to track down. If you're doing something more than once, consider splitting it into a function.

cpp

#include <iostream>
using namespace std;

void showWelcome() {
    cout << "Welcome to C++ lesson!" << endl;
}

int add(int a, int b) {
    return a + b;
}

int main() {
    showWelcome();
    int total = add(5, 3);
    cout << "Total: " << total;
    return 0;
}

showWelcome() just outputs something and doesn't need a return value, so it's declared void. add() takes two integers and returns an integer result, so its return type is int.

You should see

Welcome to C++ lesson! Total: 8

Info

Name your functions so it's obvious what they do. doThing() versus calculateTotal() — the second one is a lot easier to understand when you come back to read it later.

Easy traps

Watch out for mismatches between a function's return type and what it actually returns. Declaring a function as int but never returning a value can trigger a warning or error.