Programs are boring if they can't talk to you. C# makes input and output easy with the Console class. Think of the console as a chat window between your program and your user.
Writing to the Console
Console.WriteLine prints text and moves to the next line. Console.Write prints text but stays on the same line:
Console.WriteLine("Line 1"); // Prints "Line 1" then goes to next line
Console.Write("Still on "); // Prints without newline
Console.WriteLine("Line 2"); // Prints "Line 2" after "Still on "
Output:
Line 1
Still on Line 2
Reading Input from the User
Console.ReadLine reads whatever the user types until they press Enter. It returns a string:
Console.Write("What's your name? ");
string name = Console.ReadLine();
Console.WriteLine("Hello, " + name + "!");
When the program runs, it waits at ReadLine for the user to type something. Nothing happens until they press Enter.
If you're reading a number, remember it comes back as a string. You'll need to parse it:
Console.Write("Enter your age: ");
string input = Console.ReadLine();
int age = int.Parse(input);
Console.WriteLine("Next year you'll be " + (age + 1));
String Interpolation
Concatenating strings with + works, but C# has a cleaner way. String interpolation uses $ before the string and lets you embed variables directly with curly braces:
string name = "Lisa";
int age = 30;
// Old way with concatenation
Console.WriteLine("Hello, " + name + "! You are " + age + " years old.");
// New way with interpolation
Console.WriteLine($"Hello, {name}! You are {age} years old.");
Both lines print the same thing, but interpolation is easier to read and less error-prone. You can even put expressions inside the braces:
Console.WriteLine($"Next year you'll be {age + 1}");
Console.WriteLine($"Pi is approximately {Math.PI:F2}"); // F2 formats to 2 decimals