C# Fundamentals: Input and Output Essentials

C# Fundamentals: Input and Output Essentials

This guide walks you through C#’s core input and output techniques, showing how to read user data and display results reliably.

C# Output

To write data to the console, C# offers two primary methods:

System.Console.WriteLine()
System.Console.Write()

Here, System is the namespace, Console is a class within that namespace, and WriteLine and Write are its methods.

Example 1: Printing a String with WriteLine()

using System;

namespace Sample
{
    class Test
    {
        public static void Main(string[] args)
        {
            Console.WriteLine("C# is cool");
        }
    }
}

Running the program produces:

C# is cool

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Difference Between WriteLine() and Write()

WriteLine() outputs the supplied text and advances to a new line, while Write() prints text without adding a line break.

Example 2: Using WriteLine() and Write()

using System;

namespace Sample
{
    class Test
    {
        public static void Main(string[] args)
        {
            Console.WriteLine("Prints on ");
            Console.WriteLine("New line");

            Console.Write("Prints on ");
            Console.Write("Same line");
        }
    }
}

Output:

Prints on
New line
Prints on Same line

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Printing Variables and Literals

Both WriteLine() and Write() can display variables and literals.

Example 3: Variables and Literals

using System;

namespace Sample
{
    class Test
    {
        public static void Main(string[] args)
        {
            int value = 10;

            // Variable
            Console.WriteLine(value);
            // Literal
            Console.WriteLine(50.05);
        }
    }
}

Result:

10
50.05

---

Concatenating Strings with the + Operator

Strings can be combined using the + operator during output.

Example 4: Concatenated Output

using System;

namespace Sample
{
    class Test
    {
        public static void Main(string[] args)
        {
            int val = 55;
            Console.WriteLine("Hello " + "World");
            Console.WriteLine("Value = " + val);
        }
    }
}

Result:

Hello World
Value = 55

---

Formatted Strings – A Cleaner Approach

Formatted strings let you embed placeholders that are replaced at runtime, improving readability and reducing errors.

For example, instead of:

Console.WriteLine("Value = " + val);

use:

Console.WriteLine("Value = {0}", val);

Here, {0} is a placeholder for val. Multiple variables are handled with additional placeholders.

Example 5: Using String Formatting

using System;

namespace Sample
{
    class Test
    {
        public static void Main(string[] args)
        {
            int firstNumber = 5, secondNumber = 10, result;
            result = firstNumber + secondNumber;
            Console.WriteLine("{0} + {1} = {2}", firstNumber, secondNumber, result);
        }
    }
}

Output:

5 + 10 = 15

This method is more readable and less error‑prone than manual concatenation.

Learn more about string formatting in C# string formatting.

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C# Input

The most straightforward way to capture user input is Console.ReadLine(). For more granular input, Read() and ReadKey() are also available.

Example 6: Reading a String from the User

using System;

namespace Sample
{
    class Test
    {
        public static void Main(string[] args)
        {
            string testString;
            Console.Write("Enter a string - ");
            testString = Console.ReadLine();
            Console.WriteLine("You entered '{0}'", testString);
        }
    }
}

Output:

Enter a string - Hello World
You entered 'Hello World'

---

Understanding ReadLine(), Read(), and ReadKey()

• ReadLine(): Reads an entire line from the input stream and returns it as a string.
• Read(): Reads the next character and returns its ASCII value.
• ReadKey(): Captures a key press without waiting for the Enter key; useful for pause prompts.

For deeper insight, see the discussion on StackOverflow titled “Difference between Console.Read() and Console.ReadLine?”.

---

Example 7: Demonstrating Read() and ReadKey()

using System;

namespace Sample
{
    class Test
    {
        public static void Main(string[] args)
        {
            int userInput;

            Console.WriteLine("Press any key to continue...");
            Console.ReadKey();
            Console.WriteLine();

            Console.Write("Input using Read() - ");
            userInput = Console.Read();
            Console.WriteLine("Ascii Value = {0}", userInput);
        }
    }
}

Output:

Press any key to continue...
x
Input using Read() - Learning C#
Ascii Value = 76

Notice that ReadKey() displays the key immediately, while Read() captures a line but only returns the first character’s ASCII code (here, 76 for ‘L’).

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Reading Numeric Values

While strings are read directly, numeric types require conversion. The Convert class provides straightforward methods.

Example 8: Converting User Input to Numbers

using System;

namespace UserInput
{
    class MyClass
    {
        public static void Main(string[] args)
        {
            string userInput;
            int intVal;
            double doubleVal;

            Console.Write("Enter integer value: ");
            userInput = Console.ReadLine();
            intVal = Convert.ToInt32(userInput);
            Console.WriteLine("You entered {0}", intVal);

            Console.Write("Enter double value: ");
            userInput = Console.ReadLine();
            doubleVal = Convert.ToDouble(userInput);
            Console.WriteLine("You entered {0}", doubleVal);
        }
    }
}

Result:

Enter integer value: 101
You entered 101
Enter double value: 59.412
You entered 59.412

Convert’s ToInt32() and ToDouble() methods transform the input string into the desired numeric type. A full list of conversion methods is available in the .NET documentation.

Explore alternative numeric input strategies in Reading an integer from user input.