Switch expressions with patterns in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a switch expression in C#?

A switch expression is a concise way to select a value based on matching patterns. It returns a value directly and uses the syntax with 'switch' and '=>' arrows.

intermediate

How do patterns enhance switch expressions?

Patterns allow matching on types, values, or conditions inside switch expressions, making them more powerful and expressive than simple value matching.

beginner

Example: What does this switch expression do?

object obj = 5;
string result = obj switch {
  int i => $"Integer {i}",
  string s => $"String {s}",
  _ => "Unknown"
};

It checks the type of obj. If obj is an int, it returns "Integer 5". If obj is a string, it returns "String" plus the string value. Otherwise, it returns "Unknown".

beginner

What does the underscore (_) mean in switch expressions?

The underscore (_) is a discard pattern that matches anything not matched by previous cases. It acts like a default case.

intermediate

Can switch expressions use relational patterns? Give an example.

Yes, switch expressions can use relational patterns like <, >, <=, >=. Example:

int age = 20;
string category = age switch {
  < 13 => "Child",
  < 20 => "Teen",
  _ => "Adult"
};

What keyword starts a switch expression in C#?

A switch

B case

C match

D select

Switch expressions start with the 'switch' keyword followed by the expression to match.

In a switch expression, what does the '=>' symbol mean?

A It declares a variable

B It means 'or'

C It ends the switch

D It separates the pattern from the result expression

The '=>' separates the pattern on the left from the result expression on the right.

What pattern matches any value not matched before in a switch expression?

A default

B null

C _

D else

The underscore (_) is the discard pattern that matches anything else.

Which of these is a valid pattern in a switch expression?

A int = 5

B int i

C int => 5

D int ?

The pattern 'int i' matches any int and assigns it to variable i.

Can switch expressions return values directly?

A Yes

B No

C Only in C# 7

D Only with enums

Switch expressions always return a value directly.

Explain how switch expressions with patterns work in C#.

Think about how you choose an option based on matching conditions.

Write a simple switch expression that returns "Even" or "Odd" for an integer input.

Use modulo operator (%) inside a pattern or condition.