Functions

Overview

Functions break large tasks into smaller, modular, reusable pieces. A function must be declared (prototype) before it is used, and defined (implementation) somewhere in the code.

Syntax

cpp

// Declaration (Prototype)
int add(int a, int b);

int main() {
    int sum = add(5, 3); // Calling
    return 0;
}

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

Common Pitfalls

Forgetting to declare the function before `main()`, resulting in a 'was not declared in this scope' compiler error.

Interview Tips

Explain that prototypes allow functions to call each other regardless of the order they are defined in the file. Header files (.h) are essentially lists of function prototypes.

Real-World Example

Separating declaration from definition.

example

cpp

#include <iostream>
using namespace std;

// Prototype
void printBanner();

int main() {
    printBanner(); // Call
    return 0;
}

// Implementation
void printBanner() {
    cout << "======================\n";
    cout << "   SYSTEM ACTIVATED   \n";
    cout << "======================\n";
}

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