C++ Program to Print Number Entered by User

Introduction

Printing an input number is one of the most basic tasks in C++ or any other programming language. It serves as an introduction to input and output (I/O) operations. This simple exercise helps beginners understand how to interact with users, forming the foundation for more advanced programming concepts. In C++, this is typically done using cin for input and cout for output, both of which are part of the standard <iostream> library.

In this article, you will learn how to develop a C++ program that prompts a user to enter a number and then prints that number. Explore different methods to enhance user interaction and error handling to ensure the program behaves correctly in different input scenarios.

Basic C++ Program to Print Number Entered by User

Accepting User Input

1. Include the necessary header files.

2. Declare the main function.

3. Initialize the variable to store user input.

4. Prompt the user to enter a number.

5. Use cin to capture user input.

6. Output the number back to the user.

   cpp Copy

   #include <iostream>
   using namespace std;
   
   int main() {
       int userNumber;
       cout << "Please enter a number: ";
       cin >> userNumber;
       cout << "You entered: " << userNumber << endl;
       return 0;
   }
   

   Explain Code

   Here, the program includes the <iostream> header, which is essential for C++ input and output streams. The cin object is used for input, and cout is used for output. By prompting the user and then displaying the entered number, you complete a basic I/O cycle.

Validating User Input is a Number

1. Ensure cin successfully reads an integer.

2. Implement simple error handling.

   cpp Copy

   #include <iostream>
   using namespace std;
   
   int main() {
       int userNumber;
       cout << "Please enter a number: ";
       if (cin >> userNumber) {
           cout << "You entered: " << userNumber << endl;
       } else {
           cout << "Error: Invalid input." << endl;
           cin.clear(); // Clear error flag
           cin.ignore(numeric_limits<streamsize>::max(), '\n'); // Ignore wrong input
       }
       return 0;
   }
   

   Explain Code

   This enhanced version checks whether the input operation succeeds. If cin >> userNumber fails (e.g., if the user enters a non-numeric value), the program prints an error message. The cin.clear() function resets the error state of cin, allowing further I/O operations. cin.ignore(...) skips the rest of the incorrect input.

Advanced User Interaction in C++

Using Loops for Continuous Input

1. Allow the user to enter multiple numbers until a command (like exit) is given.

2. Utilize a loop to maintain the program running.

   cpp Copy

   #include <iostream>
   #include <string>
   using namespace std;
   
   int main() {
       int userNumber;
       string input;
       while (true) {
           cout << "Enter a number or 'exit' to quit: ";
           if (!(cin >> userNumber)) {
               cin.clear();
               cin >> input;
               if (input == "exit") {
                   break;
               } else {
                   cout << "Invalid command or number! Please try again." << endl;
                   cin.ignore(numeric_limits<streamsize>::max(), '\n');
               }
           } else {
               cout << "You entered: " << userNumber << endl;
           }
       }
       cout << "Program ended." << endl;
       return 0;
   }
   

   Explain Code

   In this example, the program runs in a continuous loop, processing user inputs. If the user types exit, the loop breaks, and the program terminates. This method enhances user interaction by not requiring the program to be restarted for each input.

Conclusion

Developing a C++ program to print a number entered by the user is an excellent starting point for understanding the basics of I/O in C++. By experimenting with different coding practices outlined here, such as input validation and loop-based continuous input, you foster enhanced user interactions and robust program designs. Integrate these methods into your programs to build more interactive and error-free applications.