Accept user input

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Programs become truly powerful when they can interact with the people using them. C#'s Console.ReadLine() method lets you pause your program, wait for the user to type something, and capture that information.

Using Console.ReadLine()

Think of the Console.ReadLine() method as a question prompt. When your program hits this line, it waits until the user types their answer and presses the Enter key before continuing.

To save the user's answer, you must "catch" it using a variable:

string favoriteColor = Console.ReadLine();
Console.WriteLine("Oh, I love " + favoriteColor + " too!");

In this code, favoriteColor is a variable (a container that holds a value). When you run this program, it waits for input. If the user types Orange and presses Enter, the output is:

Orange
Oh, I love Orange too!

You can try running this code yourself in the C# Code Editor.

Add a space at the end of your prompt

To make the user input more readable, combine Console.Write() with Console.ReadLine():

Console.Write("What is your favorite color? ");
string favoriteColor = Console.ReadLine();
Console.WriteLine("Oh, I love " + favoriteColor + " too!");

Notice the space at the end of the prompt: "What is your favorite color? ". Without it, the user's input would look glued to your text: What is your favorite color?Orange. Adding a space makes it clearer.

Understanding data types

Every value in C# has a data type, which tells the computer what kind of value it is. Some common data types are:

• String (string): Text wrapped in quotes, like "Blue" or "25". Even a number becomes text when it's inside quotes.
• Integer (int): A whole number without quotes, like 25 or 100. You can do math with these.

Why does this matter? C# treats these types differently. You can add numbers together (25 + 1 equals 26), but you can't directly add a number to text without special handling.

Console.ReadLine() always returns a string

An essential rule to remember is that Console.ReadLine() always returns text (a string), even if the user types a number. For example:

string age = Console.ReadLine();
Console.WriteLine(age + 1); // This causes an error!

If you run this code and type 25, the program won't print 26. Instead, it tries to add 1 to the text "25", which C# doesn't allow. This is a common beginner mistake!

To do math with user input, you'd need to convert the text to a number first—but we'll cover that later. For now, remember: whatever the user types is always treated as text.