Switch expression behavior in Go - Step-by-Step Execution

Concept Flow - Switch expression behavior

Start switch expression

↓

Evaluate expression once

↓

Compare expression to case values

↓

Match found?

No→Execute default case if present

↓

Execute matched case block

↓

Exit switch

The switch expression is evaluated once, then compared to each case value in order. When a match is found, its block runs and the switch exits.

Execution Sample

Go

package main
import "fmt"
func main() {
  x := 2
  switch x {
  case 1: fmt.Println("One")
  case 2: fmt.Println("Two")
  default: fmt.Println("Other")
  }
}

This code checks the value of x and prints the matching case's message.

Execution Table

Step	Expression Value	Case Checked	Match?	Action	Output
1	2	case 1	No	Skip case 1
2	2	case 2	Yes	Execute case 2 block	Two
3	2	default	Skipped	Switch exits after match

💡 Switch exits after executing the matched case block (case 2).

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
x	2	2	2	2

Key Moments - 2 Insights

Why does the switch stop after matching case 2 and not check the default case?

Because once a matching case is found (step 2 in execution_table), the switch executes that case block and exits immediately without checking further cases.

Is the switch expression evaluated multiple times for each case?

No, the expression is evaluated once at the start (step 1), then compared to each case value.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output at step 2?

A One

B Other

C Two

D No output

💡 Hint

Check the 'Output' column for step 2 in the execution_table.

At which step does the switch expression get evaluated?

A Step 1

B Step 2

C Step 3

D It is evaluated multiple times

💡 Hint

Look at the 'Expression Value' column in the execution_table.

If x was 3, which case would execute according to the execution_table logic?

A case 1

B default

C case 2

D No case executes

💡 Hint

Recall that if no case matches, the default case runs.

Concept Snapshot

switch expression {
  case value1:
    // runs if expression == value1
  case value2:
    // runs if expression == value2
  default:
    // runs if no case matches
}

- Expression evaluated once
- Cases checked in order
- Executes first matching case and exits
- Default runs if no match

Full Transcript

In Go, a switch expression is evaluated once at the start. Then, each case is checked in order to see if it matches the expression's value. When a match is found, the corresponding case block runs and the switch exits immediately. If no case matches, the default block runs if it exists. For example, if x equals 2, the switch checks case 1 (no match), then case 2 (match), runs that block, and stops without checking default. This behavior helps write clear multi-way decisions without repeated expression evaluation.