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Swap two numbers using pointers

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C++ Program to Swap Two Numbers Using Pointers

Understanding Pointers in C++

Pointers are powerful C++ data types that store memory addresses rather than direct values. They provide direct access to memory locations, enabling efficient data manipulation and memory management. Read More.

Pointer Syntax

<data_type> *pointer_name;

The asterisk (*) operator is used to:

Declare a pointer variable
Dereference a pointer (access the value at the stored address)

Example Usage

int *ptr;        // Pointer declaration
int value = 12;
ptr = &value;    // Assign address of value to pointer
cout << ptr;     // Output: Memory address of value
cout << *ptr;    // Output: 12 (dereferenced value)

Pointer-Based Number Swapping Algorithm

Approach

The program demonstrates how to swap two numbers using pointers by:

1. Storing values in variables

2. Creating pointers to their memory addresses

3. Using a temporary pointer for the swap operation

4. Manipulating values through dereferenced pointers

Step-by-Step Algorithm

1. Prompt user for two integer inputs

2. Declare three pointers: two for the numbers, one temporary

3. Assign addresses of input variables to pointers

4. Perform swap using dereferenced pointers

5. Display results after swapping

Complete C++ Implementation

#include <iostream>
using namespace std;

int main() {
    int a, b;
  
    // Get user input
    cout << "Enter two numbers separated by space: ";
    cin >> a >> b;
  
    // Display original values
    cout << "\nOriginal values:";
    cout << "\nFirst number = " << a;
    cout << "\nSecond number = " << b;

    // Pointer declaration and initialization
    int *ptr1 = &a, *ptr2 = &b;
    int temp;

    // Swap values using pointers
    temp = *ptr1;    // Store value of a in temp
    *ptr1 = *ptr2;   // Assign value of b to a
    *ptr2 = temp;    // Assign original value of a (from temp) to b

    // Display swapped values
    cout << "\n\nValues after swapping:";
    cout << "\nFirst number = " << a;
    cout << "\nSecond number = " << b;
    cout << "\n\nMemory addresses:";
    cout << "\nAddress of first number: " << ptr1;
    cout << "\nAddress of second number: " << ptr2;

    return 0;
}

Sample Output

Enter two numbers separated by space: 14 16
Original values:
First number = 14
Second number = 16

Values after swapping:
First number = 16
Second number = 14

Memory addresses:
Address of first number: 0x7ffd5a2b5a68
Address of second number: 0x7ffd5a2b5a6c

Best Practices

Always initialize pointers (use nullptr in modern C++)
Check for null pointers before dereferencing
Avoid dangling pointers (pointers to freed memory)
Prefer references over pointers when possible for safer code
Use smart pointers (unique_ptr, shared_ptr) for automatic memory management