Input & Output

Console.WriteLine & Console.Write

`Console.WriteLine` prints text followed by a new line. `Console.Write` prints without a line break, useful for prompts where you want the user's response to appear on the same line.

Console.Write("Enter your age: ");
Console.WriteLine("This appears on a new line after input.");

Console.ReadLine

`Console.ReadLine()` reads a full line of text typed by the user (up until they press Enter) and always returns a `string?` (nullable), so numeric input needs converting — as covered in the type conversion lesson, TryParse is the safer choice for real user input.

Console.Write("Enter your age: ");
string? input = Console.ReadLine();

if (int.TryParse(input, out int age))
{
    Console.WriteLine($"Next year you'll be {age + 1}.");
}
else
{
    Console.WriteLine("That doesn't look like a valid age.");
}

Console.ReadKey

Unlike ReadLine (which waits for Enter), Console.ReadKey() reads a single keypress immediately, without needing Enter pressed afterward — useful for "Press any key to continue" prompts or simple menu navigation.

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

String Interpolation

The `$` prefix lets you embed expressions directly inside a string using curly braces — far more readable than manual string concatenation with the + operator, and it can embed any valid C# expression, not just simple variables.

string name = "Priya";
int score = 92;
Console.WriteLine($"{name} scored {score}% — {(score >= 90 ? "Excellent" : "Good")}!");

Format Specifiers

A colon inside an interpolated expression applies a format specifier, controlling exactly how a value displays — essential for currency, percentages, and controlling decimal places.

decimal price = 1234.5m;
Console.WriteLine($"{price:C}");   // $1,234.50
Console.WriteLine($"{price:N2}");  // 1,234.50
Console.WriteLine($"{0.256:P}");   // 25.60%

Alignment can also be controlled with a comma inside the braces — a positive number right-aligns within that many characters, negative left-aligns, useful for building neatly columned console output.

Console.WriteLine($"{"Name",-10}{"Score",5}");
Console.WriteLine($"{"Priya",-10}{92,5}");
Console.WriteLine($"{"Alex",-10}{78,5}");

Escape Sequences & Verbatim Strings

A backslash inside a regular string introduces an escape sequence — a way to represent characters that would otherwise be hard or impossible to type directly.

For strings containing many backslashes (like a Windows file path), a verbatim string — prefixed with @ — treats backslashes as literal characters, removing the need to escape them.

string regular = "C:\\Users\\Alex\\Documents"; // every backslash must be doubled
string verbatim = @"C:\Users\Alex\Documents";   // reads naturally, no escaping needed

Colored Console Output

Console.ForegroundColor and Console.BackgroundColor let you color console text — a small but genuinely useful touch for CLI tools that highlight errors, warnings, or success messages.

Console.ForegroundColor = ConsoleColor.Red;
Console.WriteLine("Error: something went wrong.");
Console.ResetColor(); // always reset afterward, or every later line stays red too!

A Complete Example

Console.Write("Enter a number: ");
if (int.TryParse(Console.ReadLine(), out int number))
{
    Console.WriteLine($"Double of {number} is {number * 2}.");
}
else
{
    Console.WriteLine("That wasn't a valid number.");
}

Common Beginner Mistakes

FAQs

Key Takeaways

Summary

Console I/O and string formatting are the tools you'll reach for constantly while building and debugging every program in this course. Next, you'll learn how to make your programs actually make decisions with conditional statements.