📅 Date: Jan 8, 2026
🔥 Topic: Functions (Part 3): Pass by Value vs Reference

🤔 The Problem

Today I tried to write a function to swap two numbers. It seemed simple, but when I ran it, the numbers didn't swap in main().

This happened because of Pass by Value.

1️⃣ Pass by Value (The Photocopy)

When we pass variables normally, C++ creates a copy of that variable.
Result: Changes inside the function do NOT affect the original variable.

2️⃣ Pass by Reference (The Original)

To actually modify the original variable, we need to pass its Reference using the & symbol.
Result: The function gets access to the actual memory address of the variable.

💻 Day 8 Code: The Swap Test

Here is the code that finally worked using Pass by Reference. 

#include <iostream>
using namespace std;

// Pass by Value (Won't work)
void fakeSwap(int a, int b) {
    int temp = a;
    a = b;
    b = temp;
}

// Pass by Reference (Works!)
// Notice the '&' symbol
void realSwap(int &a, int &b) {
    int temp = a;
    a = b;
    b = temp;
}

int main() {
    int x = 10, y = 20;

    cout << "Original: " << x << " " << y << endl;

    // Trying Fake Swap
    fakeSwap(x, y);
    cout << "After Fake Swap: " << x << " " << y << " (No Change)" << endl;

    // Trying Real Swap
    realSwap(x, y);
    cout << "After Real Swap: " << x << " " << y << " (Swapped!)" << endl;

    return 0;
}

💭 Thoughts

The & operator is powerful. It allows functions to directly manipulate memory. It feels like giving someone the key to your house (Reference) vs giving them a photo of your house (Value).