In C#, user input refers to the data or values that are provided by the user during the execution of a program. Collecting user input is essential for creating interactive programs that can process dynamic data and respond accordingly. The Console.ReadLine() method is commonly used to capture input from the user in console-based applications.

In this tutorial, we will explore different ways to handle user input in C# programs, including reading text, converting input types, and handling invalid inputs.

1. Reading Input from the User

The most basic way to read input from the user is through the Console.ReadLine() method. This method reads the entire line of input as a string.

Example:

using System;

class Program
{
    static void Main()
    {
        // Prompt the user for input
        Console.Write("Enter your name: ");
        
        // Capture user input
        string name = Console.ReadLine();
        
        // Output the entered name
        Console.WriteLine("Hello, " + name + "!");
    }
}

Output:

Enter your name: John
Hello, John!

In this example:

• Console.Write() is used to display a prompt to the user.
• Console.ReadLine() reads the user’s input and stores it in the variable name.
• Console.WriteLine() then displays the greeting message with the user’s name.

2. Converting User Input to Other Data Types

Since Console.ReadLine() returns a string, you’ll often need to convert the input to other data types (e.g., integers, doubles, or booleans) to perform calculations or logic. This can be done using type conversion methods like int.Parse(), double.Parse(), bool.Parse(), or using Convert.ToInt32(), Convert.ToDouble(), etc.

Example 1: Converting a String to an Integer

using System;

class Program
{
    static void Main()
    {
        // Prompt the user to enter a number
        Console.Write("Enter your age: ");
        
        // Capture user input and convert it to an integer
        int age = int.Parse(Console.ReadLine());
        
        // Output the age
        Console.WriteLine("Your age is: " + age);
    }
}

Output:

Enter your age: 25
Your age is: 25

In this example, int.Parse() converts the string input to an integer. However, you should be cautious because if the user enters a non-numeric value, it will throw an exception.

3. Handling Invalid Input Using Try-Catch

To handle invalid inputs (e.g., the user entering a letter when a number is expected), you can use a try-catch block to catch exceptions and prompt the user to enter the correct value.

Example 2: Handling Invalid Input with Try-Catch

using System;

class Program
{
    static void Main()
    {
        int age;
        
        // Prompt the user to enter a number
        Console.Write("Enter your age: ");
        
        // Try to read and convert the input
        try
        {
            age = int.Parse(Console.ReadLine());
            Console.WriteLine("Your age is: " + age);
        }
        catch (FormatException)
        {
            Console.WriteLine("Please enter a valid number.");
        }
    }
}

Output (Invalid Input):

Enter your age: abc
Please enter a valid number.

In this example:

• int.Parse() is used to convert the input to an integer.
• If the user enters an invalid value (e.g., non-numeric input), a FormatException is thrown, and the catch block handles the error by displaying a friendly message.

4. Using TryParse for Safe Input Handling

A safer alternative to int.Parse() is the TryParse() method. This method attempts to convert the input and returns a Boolean value indicating whether the conversion was successful or not, without throwing an exception.

Example 3: Using TryParse to Avoid Exceptions

using System;

class Program
{
    static void Main()
    {
        int age;
        
        // Prompt the user to enter a number
        Console.Write("Enter your age: ");
        
        // Try to parse the input safely
        bool success = int.TryParse(Console.ReadLine(), out age);
        
        if (success)
        {
            Console.WriteLine("Your age is: " + age);
        }
        else
        {
            Console.WriteLine("Invalid input. Please enter a valid number.");
        }
    }
}

Output (Valid Input):

Enter your age: 30
Your age is: 30

Output (Invalid Input):

Enter your age: abc
Invalid input. Please enter a valid number.

In this example:

• TryParse() tries to convert the input string to an integer.
• If the conversion is successful, it returns true, and the age is printed.
• If the conversion fails (e.g., if the user enters non-numeric text), it returns false, and an error message is displayed.

5. Reading Other Data Types

You can use similar methods to read other data types, such as double, bool, or DateTime, with appropriate parsing or conversion methods.

Example 4: Reading a Boolean Value

using System;

class Program
{
    static void Main()
    {
        // Prompt the user to enter yes or no
        Console.Write("Do you agree? (yes/no): ");
        
        // Capture user input and convert it to a boolean
        string input = Console.ReadLine().ToLower();
        bool isAgreed = (input == "yes");
        
        if (isAgreed)
        {
            Console.WriteLine("You agreed.");
        }
        else
        {
            Console.WriteLine("You disagreed.");
        }
    }
}

Output:

Do you agree? (yes/no): yes
You agreed.

In this example:

• The input is converted to lowercase using ToLower(), and a simple comparison is used to determine if the user entered "yes".

6. Reading a Date

If you need to read a date from the user, you can use DateTime.Parse() or DateTime.TryParse() to handle date input.

Example 5: Reading a Date from the User

using System;

class Program
{
    static void Main()
    {
        // Prompt the user to enter a date
        Console.Write("Enter your birthdate (MM/dd/yyyy): ");
        
        // Try to parse the input as a date
        DateTime birthDate;
        if (DateTime.TryParse(Console.ReadLine(), out birthDate))
        {
            Console.WriteLine("Your birthdate is: " + birthDate.ToShortDateString());
        }
        else
        {
            Console.WriteLine("Invalid date format.");
        }
    }
}

Output (Valid Date):

Enter your birthdate (MM/dd/yyyy): 01/15/1990
Your birthdate is: 01/15/1990

Output (Invalid Date):

Enter your birthdate (MM/dd/yyyy): abc
Invalid date format.

Conclusion

User input in C# is a fundamental part of building interactive programs. By using methods like Console.ReadLine(), int.Parse(), TryParse(), and DateTime.Parse(), you can capture and process user data. To ensure smooth interaction, always consider handling invalid inputs with error handling mechanisms like try-catch or TryParse() to avoid crashes and provide helpful feedback to users.