C++ Program to Swap Two Numbers

Photo by Antonio Batinić

Here’s a simple C++ program to swap two numbers, along with a detailed explanation:

#include <iostream> 
 // This is a preprocessor directive that includes the standard input-output stream library
using namespace std;
  // This line tells the compiler to use the standard namespace
int main() { 
// This is the main function, the entry point of a C++ program
    int num1, num2, temp;  
// Declaration of integer variables
    // Prompt the user to enter two numbers
    cout << "Enter first number: ";
    cin >> num1; 
 // Read the first number from the user
    cout << "Enter second number: ";
    cin >> num2; 
 // Read the second number from the user
    // Display the numbers before swapping
    cout << "Before swapping: " << endl;
    cout << "num1 = " << num1 << ", num2 = " << num2 << endl;
    // Swap the numbers using a temporary variable
    temp = num1; 
 // Store the value of num1 in temp
    num1 = num2; 
 // Assign the value of num2 to num1
    num2 = temp; 
 // Assign the value of temp (original num1) to num2
    // Display the numbers after swapping
    cout << "After swapping: " << endl;
    cout << "num1 = " << num1 << ", num2 = " << num2 << endl;
    return 0; 
 // The program returns 0 to indicate that it ended successfully
}

Description

1. Preprocessor Directive:
   • #include
     • This line tells the preprocessor to include the iostream library, which is necessary for input and output operations in C++.
2. Namespace Declaration:
   • using namespace std;
     • The std namespace includes all the features of the C++ Standard Library. By including this line, we don’t need to prefix standard library names with std::.
3. Main Function:
   • int main() { … }
     • The main function is the starting point of every C++ program. It returns an integer value, which is typically used to indicate whether the program ended successfully.
4. Variable Declarations:
   • int num1, num2, temp;
     • These lines declare three integer variables: num1, num2, and temp.
5. Input Statements:
   • cout << “Enter first number: “;
     • This line prints a prompt to the console asking the user to enter the first number.
   • cin >> num1;
     • This line reads an integer input from the user and stores it in the num1 variable.
   • cout << “Enter second number: “;
     • This line prints a prompt to the console asking the user to enter the second number.
   • cin >> num2;
     • This line reads an integer input from the user and stores it in the num2 variable.
6. Display Before Swapping:
   • cout << “Before swapping: ” << endl;
     • This line prints a message indicating that the numbers displayed next are before swapping.
   • cout << “num1 = ” << num1 << “, num2 = ” << num2 << endl;
     • These lines print the values of num1 and num2 before swapping.
7. Swapping Logic:
   • temp = num1;
     • This line stores the value of num1 in the temp variable.
   • num1 = num2;
     • This line assigns the value of num2 to num1.
   • num2 = temp;
     • This line assigns the value of temp (which holds the original value of num1) to num2.
8. Display After Swapping:
   • cout << “After swapping: ” << endl;
     • This line prints a message indicating that the numbers displayed next are after swapping.
   • cout << “num1 = ” << num1 << “, num2 = ” << num2 << endl;
     • These lines print the values of num1 and num2 after swapping.
9. Return Statement:
   • return 0;
     • This statement ends the main function and returns the value 0 to the operating system. A return value of 0 typically indicates that the program executed successfully.

This program takes two integers as input from the user, swaps their values using a temporary variable, and displays the numbers before and after swapping.