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switch and fallthrough

Learn multi-branch switch and the fallthrough behavior.

switch and fallthrough

switch compares a value against several possibilities. A case can take several values separated by commas; the switch ends when the matching case finishes:

switch gun {
case "Cumartesi", "Pazar":
    fmt.Println("hafta sonu")
case "Cuma":
    fmt.Println("son iş günü")
default:
    fmt.Println("iş günü")
}

To deliberately continue into the next case write fallthrough; it is rarely needed.

Expressionless switch

A switch without a value is a readable form of a long if-else chain; each case is a bool expression:

switch {
case sicaklik < 0:
    fmt.Println("donuyor")
case sicaklik < 20:
    fmt.Println("serin")
default:
    fmt.Println("sıcak")
}

Cases are tried from top to bottom; the first true one runs.

Practice Kind of day

Write gunTuru(gun string) string: "hafta sonu" for "Cumartesi" and "Pazar", "iş günü" otherwise. Print gunTuru("Pazar") and gunTuru("Salı") on one line.

Starter code

main.go
package main

import "fmt"

func main() {
    // buraya yaz
}

Sample solution

main.go
package main

import "fmt"

func gunTuru(gun string) string {
    switch gun {
    case "Cumartesi", "Pazar":
        return "hafta sonu"
    default:
        return "iş günü"
    }
}

func main() {
    fmt.Println(gunTuru("Pazar"), gunTuru("Salı"))
}

Expected output

hafta sonu iş günü

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Does <code>fallthrough</code> check the next case's condition?

  • It runs all cases
  • It jumps to default
  • No; it runs the next case's body without checking its condition Correct answer
  • Yes, it runs it if the condition is true

Explanation: fallthrough is an unconditional jump; that's why it can cause surprising behavior and is used carefully.

2 Multiple values

Question 
switch gun {
case "Cumartesi"____ "Pazar":
    fmt.Println("hafta sonu")
}
Answer 
switch gun {
case "Cumartesi", "Pazar":
    fmt.Println("hafta sonu")
}

Explanation: A case takes several values separated by commas.

3 Input and output

Term Meaning
"Pazar" hafta sonu
"Cuma" son iş günü
"Salı" iş günü (default)
sicaklik = -3 donuyor

All lessons in Beginner

1 Go basics

  1. What is Go?
  2. Installing Go
  3. Your first program
  4. go run and go build
  5. Comments and semicolons
  6. Summary - Go basics

2 Modules

  1. go mod init
  2. package and import
  3. The main package
  4. Multiple files
  5. go.sum and dependencies
  6. Summary - Modules

3 Variables

  1. Declaration with var
  2. Short declaration :=
  3. const and iota
  4. Zero value
  5. Type inference
  6. Summary - Variables

4 Data types

  1. int and float
  2. bool and string
  3. byte and rune
  4. Type conversion
  5. Type definitions
  6. Summary - Data types

5 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Command-line menu

6 Functions

  1. func declaration
  2. Parameters and return
  3. Multiple return
  4. Variadic functions
  5. Anonymous functions
  6. Summary - Functions

7 Control flow

  1. if, else if, else
  2. for loop
  3. Iterating with range
  4. switch and fallthrough
  5. break and continue
  6. Summary - Control flow

8 Array and slice

  1. Array declaration
  2. Slice declaration
  3. Appending with append
  4. Sub-slice
  5. len and cap
  6. Summary - Array and slice

9 Project: Shopping cart

  1. Product struct
  2. Adding to cart
  3. Computing total
  4. Printing the cart

10 Map

  1. Map declaration
  2. Adding elements
  3. Looking up in a map
  4. Deleting from a map
  5. Iterating a map with range
  6. Summary - Map

11 String

  1. String and byte
  2. String concatenation
  3. Conversion with strconv
  4. The strings package
  5. Rune and UTF-8
  6. Summary - String

12 Pointer

  1. What is a pointer?
  2. & and * operators
  3. The new function
  4. Pointers and functions
  5. Nil pointer
  6. Summary - Pointer

13 Struct

  1. Struct declaration
  2. Creating a struct
  3. Field access
  4. Struct embedding
  5. Struct and pointer
  6. Summary - Struct

14 Methods

  1. Method declaration
  2. Pointer receiver
  3. Value receiver
  4. Methods and embedding
  5. Method chaining
  6. Summary - Methods

15 Interface and error

  1. Interface declaration
  2. Implicit satisfaction
  3. The error interface
  4. Returning errors
  5. errors.Is and errors.As
  6. Summary - Interface and error

16 Beginner final

  1. Challenge 1 - Combined program
  2. Challenge 2 - Data structure
  3. Challenge 3 - Error handling
  4. Challenge 4 - Mini app