Switch expression (modern C#) - Step-by-Step Execution

Concept Flow - Switch expression (modern C#)

Start with input value

↓

Evaluate switch expression

↓

Match input to pattern/case

↓

Return corresponding result

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End with output value

The switch expression takes an input, matches it against patterns, and returns the result of the matched case.

Execution Sample

C Sharp (C#)

string day = "Tuesday";
string type = day switch
{
    "Monday" => "Start of week",
    "Tuesday" => "Second day",
    _ => "Other day"
};

This code uses a switch expression to assign a description based on the day string.

Execution Table

Step	Input (day)	Switch Case Checked	Match?	Result Assigned
1	"Tuesday"	"Monday"	No	None
2	"Tuesday"	"Tuesday"	Yes	"Second day"
3	N/A	Stop checking	N/A	"Second day"

💡 Match found at step 2, switch expression returns "Second day" and stops.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
day	"Tuesday"	"Tuesday"	"Tuesday"	"Tuesday"
type	null	null	"Second day"	"Second day"

Key Moments - 2 Insights

Why does the switch expression stop checking after matching "Tuesday"?

Because switch expressions return the result immediately when a match is found, as shown in execution_table step 2 and 3.

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

It means 'any other value' or default case, used if no other case matches, but here it is not reached because "Tuesday" matches earlier.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of 'type' after step 1?

A "Start of week"

B null

C "Second day"

D "Other day"

💡 Hint

Check the 'Result Assigned' column at step 1 in the execution_table.

At which step does the switch expression find a match?

A Step 2

B Step 1

C Step 3

D No match found

💡 Hint

Look at the 'Match?' column in the execution_table.

If the input day was "Friday", what would the switch expression return?

A "Start of week"

B "Second day"

C "Other day"

D null

💡 Hint

Consider the underscore (_) case as the default in the switch expression.

Concept Snapshot

Switch expression syntax:
var result = input switch
{
  pattern1 => value1,
  pattern2 => value2,
  _ => defaultValue
};
It matches input to patterns and returns the matching value immediately.

Full Transcript

This example shows how a modern C# switch expression works. We start with a string variable 'day' set to "Tuesday". The switch expression checks each case in order: first "Monday", then "Tuesday". When it finds "Tuesday", it returns "Second day" immediately and stops checking further cases. The underscore (_) is a catch-all for any other value but is not reached here. The variable 'type' gets assigned the result of the switch expression. This flow helps write clear and concise code for matching values to results.