C++ Functions Pass By Reference (original) (raw)

Last Updated : 30 May, 2026

Pass by Reference is a method of passing arguments to a function where the function receives a reference (alias) to the original variable instead of a copy. This allows the function to directly modify the original value stored in memory.

• No copy of the variable is created.
• Changes made inside the function affect the original variable.
• Improves performance when working with large objects because copying is avoided. C++ `

#include using namespace std;

void updateValue(int &num){

num = num + 10;

}

int main(){

int number = 20;

cout << "Before Function Call: " << number << endl;

updateValue(number);

cout << "After Function Call: " << number << endl;

return 0;

}

`

Output

Before Function Call: 20 After Function Call: 30

Explanation

• number contains the value 20.
• The function receives number as a reference using &.
• Any modification made to num directly affects number.
• After the function call, the original value becomes 30.

Syntax

returnType functionName(dataType &parameter){

// Function body

}

C++ `

#include using namespace std;

void func(int& x) { x--; }

int main() { int a = 5; cout << a << endl; func(a); cout << a; }

`

**Explanation: The function func() receives an integer by reference. Since x refers to the original variable a, the statement x-- directly decreases a by 1. As a result, the value of a changes from 5 to 4, demonstrating that pass by reference allows a function to modify the original variable.

Swap function using Pass-By-Reference

The swap function swaps the values of the two variables it receives as arguments. Below is the C++ program to swap the values of two variables using pass-by-reference.

C++ `

#include <bits/stdc++.h> using namespace std;

// Swap function void swap(int &a, int &b) { int temp; temp = b; b = a; a = temp; }

int main() { int x = 3, y = 7;

// Before swapping
cout << "Before Swapping: " 
   << endl;
cout << "x: " << x << " y: " 
   << y << endl;

// Call the function
swap(x, y);

// After swapping
cout << "After Swapping: " 
   << endl;
cout << "x: " << x << " y: " 
   << y;
return 0;

}

`

Output

Before Swapping: x: 3 y: 7 After Swapping: x: 7 y: 3

**Explanation: In this program, the swap function swaps the values of two variables by passing them as references. When the function is called, it modifies the values of a and b directly. When we print the value of x and y after calling swap function, **x value is 7 and **y value is 3.

Pass by Reference vs Pass by Value

The following table compares the key differences between Pass by Reference and **Pass by value in C++: