Write a C++ Program of Call by Value and Call by Reference

Write a C++ Program to Demonstrate Call by Value and Call by Reference

Function calls in C++ can be done in two primary ways: Call by Value and Call by Reference. These two methods define how arguments are passed to functions and how changes made within a function affect the original data.

Understanding the difference between these two is crucial for controlling data flow, memory usage, and optimizing code performance.

🔹 Call by Value

In Call by Value, the actual value of the argument is passed to the function. A new copy of the variable is created in memory, and all operations within the function affect only the copy, not the original variable.

🔹 Call by Reference

In Call by Reference, the address (or reference) of the variable is passed to the function. Therefore, any change made inside the function **directly modifies the original variable.

✅ C++ Program to Demonstrate Both Concepts

#include <iostream>

using namespace std;

// Function using Call by Value

void callByValue(int a) {

    a = a + 10;

    cout << "Inside callByValue, value of a: " << a << endl;

}

// Function using Call by Reference

void callByReference(int &b) {

    b = b + 10;

    cout << "Inside callByReference, value of b: " << b << endl;

}

int main() {

    int x = 5, y = 5;

    cout << "Initial value of x: " << x << endl;

    callByValue(x);

    cout << "After callByValue, value of x: " << x << endl;

    cout << "\nInitial value of y: " << y << endl;

    callByReference(y);

    cout << "After callByReference, value of y: " << y << endl;

    return 0;

}

🔍 Output Explanation

Initial value of x: 5  

Inside callByValue, value of a: 15  

After callByValue, value of x: 5  

Initial value of y: 5  

Inside callByReference, value of b: 15  

After callByReference, value of y: 15

As seen above:

• In callByValue, the original variable `x` remains unchanged even after the function call.
• In callByReference, the original variable `y` is modified inside the function, and the change reflects in the `main()` function.

🧠 Why This Matters

• Call by Value is safe and protects the original data, but does not allow modification.
• Call by Reference allows modifications, which is useful for performance (avoiding copying large objects) and when intentional changes are needed.