Conditionals

Both C# and TypeScript/JavaScript support traditional conditional statements like if-else and switch-case, but C# offers additional features that enhance readability and expressiveness. In C#, if-else behaves similarly to JavaScript, evaluating boolean expressions to control flow. However, unlike JavaScript, C# enforces strict type checking—conditions must be explicitly bool, preventing common pitfalls like unintended truthy or falsy evaluations (if ("0") is true in JavaScript but invalid in C#).

C#’s switch is more powerful than JavaScript’s, thanks to pattern matching and switch expressions. Traditional switch-case works similarly in both languages. C#’s pattern matching allows matching on types, constants, and even properties, making conditionals more expressive (case int n when n > 10:). Additionally, switch expressions in C# provide a concise, functional-style alternative, returning values directly without requiring break statements. JavaScript lacks an equivalent, making C# conditionals more structured and safer against common errors like accidental fall-through.

If-Else

if (x == 5) { /* ... */ }
if (x < 5) { /* ... */ }
if (x >= 5) { /* ... */ }
if (x % 5 == 0) { /* ... */ }

if (y == 10) {

} else {

}

if (x == 5) { /* ... */ }
if (x < 5) { /* ... */ }
if (x >= 5) { /* ... */ }
if (x % 5 == 0) { /* ... */ }

if (y == 10) {

} else {

}

TIP

See below for how we can combine pattern matching with if conditions

If you're coming from the C# side, then one key topic to understand is the difference between == (loose equality) and === (strict equality) in JavaScript:

console.log(5 == "5");  // true (type coercion: string converted to number)
console.log(5 === "5"); // false (different types)

console.log(false == 0);  // true (both coerced to `0`)
console.log(null == undefined); // true (special coercion rule)

By default, === is the safer comparison operator to use!

C# only has strict equality and does not have the same concept.

Switch-Case

switch (x) {
  case 0:
    console.log("You win a dollar!");
    break;
  case 5:
    console.log("You win a car!");
    break;
  default:
    console.log("Play again!");
    break;
}

switch (x) {
  case 0:
    Console.WriteLine("You win a dollar!");
    break;
  case 5:
    Console.WriteLine("You win a car!");
    break;
  default:
    Console.WriteLine("Play again!");
    break;
}

TIP

See below for how we can combine pattern matching with switch-case

Ternary

let y = x > 5 ? "yes" : "no";

var y = x > 5 ? "yes" : "no";

C# Pattern Matching

C# has two additional ways of representing conditionals. The first is pattern matching.

Switch-Case

// Single expression
switch (x) {
  case <= 100 when x > 98: // 👈 Note the pattern
    Console.WriteLine("You got an A+!");
    break;
  case <= 98 when x >= 90: // 👈 Note the pattern
    Console.WriteLine("You got an A!");
    break;
  default:
    Console.WriteLine("You passed!");
    break;
}

// Tuple expression
switch ( (coursework, midterm, finals) ) {
  case (> 80, > 90, > 95): // 👈 Note the pattern
  case (> 90, > 90, > 90): // 👈 Note the pattern
    Console.WriteLine("You got an A!");
    break;
  case (> 80, > 80, > 80): // 👈 Note the pattern
    Console.WriteLine("You got a B!");
    break;
  default:
    Console.WriteLine("You passed!");
    break;
}

If-Else

var account = ("Diamond Member", 100_000);

if (account is ("Diamond Member", >= 100_000)) {
  Console.WriteLine("You are a VIP!");
} else if (account is ("Gold Member", >= 50_000)) {
  Console.WriteLine("You are a Gold Member!");
} else if (account is ("Silver Member", >= 10_000)) {
  Console.WriteLine("You are a Silver Member!");
} else {
  Console.WriteLine("You are a regular member.");
}

// You are a VIP!

Here again, we use it with a tuple type, but we can also use it with normal and anonymous types:

var account = new {
  Name = "Gigi",
  Balance = 100_000
};

if (account is { Balance: >= 100_000 }) {
  Console.WriteLine($"{account.Name} is a VIP!");
} else if (account is { Balance: >= 50_000 }) {
  Console.WriteLine($"{account.Name} is a Gold Member!");
} else if (account is { Balance: >= 10_000 }) {
  Console.WriteLine($"{account.Name} is a Silver Member!");
} else {
  Console.WriteLine($"{account.Name} is a regular member.");
}

// "Gigi is a VIP"

C# Switch Expressions

The second additional way C# can express conditionals is switch expressions:

var courseGrade = (87, 91, 98) switch {
  ( > 90, > 90, > 95) => "A+",
  ( > 80, > 90, > 90) => "A",
  ( > 80, > 80, > 80) => "B",
  _ => "C"
};

Console.WriteLine(courseGrade); // "A"

Switch expressions have a lot of utility and can condense otherwise complex trees of conditional logic! They are broken out into more detail in its own doc. If you want to explore more, checkout Tim Deschryver's excellent writeup on how powerful patterns and switch expressions are in C#