If & Else

Every program makes decisions. Do this if it's raining, do that if it's sunny. In C#, decisions are made with if, else if, and else.

The if Statement

The simplest building block: if a condition is true, run the code inside the braces. If not, skip it.

using System;

class Program {
  static void Main() {
    int age = 18;
    if (age >= 18) {
      Console.WriteLine("You can vote!");
    }
  }
}
    

else if and else

When one condition isn't enough, chain with else if. The first match wins; the rest are ignored. else catches everything that didn't match.

using System;

class Program {
  static void Main() {
    int score = 85;
    if (score >= 90) {
      Console.WriteLine("Grade A");
    } else if (score >= 75) {
      Console.WriteLine("Grade B");
    } else if (score >= 50) {
      Console.WriteLine("Grade C");
    } else {
      Console.WriteLine("Grade F");
    }
  }
}
    

Nested Conditions

You can put an if inside another if. This is nesting — useful when you need to check a second condition only after the first passes.

using System;

class Program {
  static void Main() {
    int x = 10, y = 5;
    if (x > 0) {
      if (y > 0) {
        Console.WriteLine("Both are positive");
      }
    }
  }
}
    

Boolean Expressions

In C#, the condition has to be a bool — either true or false. No tricks like in some languages where numbers count as true or false.

using System;

class Program {
  static void Main() {
    bool isRaining = true;
    if (isRaining) {
      Console.WriteLine("Take an umbrella");
    } else {
      Console.WriteLine("Enjoy the sun");
    }
  }
}