C++ Functions — Overloading, Default Args, Inline

What is a Function?

A function is a named, reusable block of code that performs a specific task. Functions reduce repetition, improve readability, and make code easier to test and maintain.

Syntax: returnType functionName(parameters) { body }

Function Basics - Declaration, Definition, Call

#include <iostream>
using namespace std;

// Function declaration (prototype) - tells compiler the signature
int add(int a, int b);
void greet(string name);

int main() {
    cout << add(3, 4) << endl;   // 7
    greet("Alice");               // Hello, Alice!
    return 0;
}

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

void greet(string name) {
    cout << "Hello, " << name << "!" << endl;
    // void functions don't need return
}

Pass by Value vs Pass by Reference

Value vs Reference vs Pointer Parameters

#include <iostream>
using namespace std;

// Pass by VALUE - copy is made, original unchanged
void doubleVal(int x) {
    x *= 2;
    cout << "Inside: " << x << endl;
}

// Pass by REFERENCE - works on original variable
void doubleRef(int &x) {
    x *= 2;
}

// Pass by CONST REFERENCE - read-only, no copy (efficient for large objects)
void printName(const string &name) {
    cout << "Name: " << name << endl;
}

// Multiple return values via references
void minMax(int a, int b, int &mn, int &mx) {
    mn = (a < b) ? a : b;
    mx = (a > b) ? a : b;
}

int main() {
    int n = 10;
    doubleVal(n);
    cout << "After doubleVal: " << n << endl;  // 10 (unchanged)

    doubleRef(n);
    cout << "After doubleRef: " << n << endl;  // 20 (changed!)

    printName("Bob");

    int lo, hi;
    minMax(7, 3, lo, hi);
    cout << "Min: " << lo << ", Max: " << hi << endl;  // 3, 7

    return 0;
}

Function Overloading and Default Arguments

Overloading and Default Arguments

#include <iostream>
using namespace std;

// Function overloading - same name, different parameter types/count
int    add(int a, int b)       { return a + b; }
double add(double a, double b) { return a + b; }
int    add(int a, int b, int c){ return a + b + c; }

// Default arguments - must be rightmost parameters
void greet(string name, string greeting = "Hello") {
    cout << greeting << ", " << name << "!" << endl;
}

// inline function - hint to compiler to expand inline (avoids call overhead)
inline int square(int x) { return x * x; }

int main() {
    cout << add(3, 4)       << endl;  // 7   (int version)
    cout << add(1.5, 2.5)   << endl;  // 4.0 (double version)
    cout << add(1, 2, 3)    << endl;  // 6   (3-arg version)

    greet("Alice");           // Hello, Alice!
    greet("Bob", "Hi");       // Hi, Bob!

    cout << square(5) << endl;  // 25

    return 0;
}