Switch expression behavior in Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a switch statement in Go?

A switch statement in Go lets you choose between many options based on the value of an expression. It is like asking multiple questions and running the code for the first true answer.

beginner

How does Go's switch differ from if-else chains?

Go's switch is cleaner and easier to read than many if-else statements. It automatically breaks after a case runs, so you don't need to write break statements like in some other languages.

beginner

What happens if no case matches in a Go switch?

If no case matches, and there is a default case, the default code runs. If there is no default, the switch does nothing and moves on.

intermediate

Can a Go switch expression have multiple values in one case?

Yes! You can list multiple values separated by commas in one case. If the switch expression matches any of those values, that case runs.

intermediate

What is a type switch in Go?

A type switch lets you check the type of an interface value. It helps you run different code depending on what kind of value you have.

What keyword is used to run code when no other case matches in a Go switch?

A else

B default

C fallback

D case

The 'default' case runs when no other case matches in a Go switch.

In Go, what happens after a case block runs in a switch statement?

A The switch automatically stops (breaks).

B It continues to the next case.

C You must write 'break' to stop.

D It throws an error.

Go switch statements automatically break after a case runs, so no explicit 'break' is needed.

Which of these is a valid way to write multiple values in one case in Go switch?

A case (1; 2; 3):

B case [1 2 3]:

C case 1, 2, 3:

D case 1|2|3:

You separate multiple values with commas in one case, like 'case 1, 2, 3:'.

What does a type switch check in Go?

A The type of a variable implementing an interface

B The value of a variable

C The length of a string

D The memory address of a variable

A type switch checks the actual type of an interface value to run different code.

Which statement about Go switch is true?

A Switch always runs all cases.

B Switch cases must be strings only.

C Switch can only check integers.

D You don't need to write 'break' after each case.

Go switch automatically breaks after a case runs; no manual 'break' is needed.

Explain how a switch statement works in Go and how it differs from if-else chains.

Think about how Go chooses which code to run based on a value.

Describe what a type switch is in Go and give an example of when you might use it.

Consider when you have a variable that can hold different types.

Practice

1. What does a switch statement do in Go?

easy

A. It runs all cases one after another.

B. It chooses one case to run based on a value or condition.

C. It only works with numbers, not strings.

D. It repeats the same case multiple times automatically.

Solution

1. Step 1: Understand switch purpose

   A switch statement selects one matching case based on a value or condition.

2. Step 2: Confirm behavior

   It stops after the first matching case, so only one case runs.

3. Final Answer:

   It chooses one case to run based on a value or condition. -> Option B

4. Quick Check:

   Switch picks one matching case [OK]

Hint: Switch picks only the first matching case [OK]

Common Mistakes:

• Thinking switch runs all cases
• Believing switch only works with numbers
• Assuming switch repeats cases automatically

2. Which of the following is the correct syntax for a basic switch statement in Go?

easy

A. switch (value) { case 1: doSomething() default: doDefault() }

B. switch value do { case 1: doSomething() default: doDefault() }

C. switch value then { case 1: doSomething() default: doDefault() }

D. switch value { case 1: doSomething() default: doDefault() }

Solution

1. Step 1: Recall Go switch syntax

   Go uses switch value { case ... } without parentheses or extra keywords.

2. Step 2: Check options

   switch value { case 1: doSomething() default: doDefault() } matches correct syntax; others add invalid keywords or parentheses.

3. Final Answer:

   switch value { case 1: doSomething() default: doDefault() } -> Option D

4. Quick Check:

   Go switch uses braces, no parentheses [OK]

Hint: No parentheses around switch value in Go [OK]

Common Mistakes:

• Adding parentheses around switch value
• Using 'then' or 'do' keywords incorrectly
• Misplacing braces or colons

3. What is the output of this Go code?

package main
import "fmt"
func main() {
  x := 3
  switch x {
  case 1:
    fmt.Println("One")
  case 2, 3:
    fmt.Println("Two or Three")
  default:
    fmt.Println("Other")
  }
}

medium

A. One

B. Other

C. Two or Three

D. No output

Solution

1. Step 1: Identify switch value and cases

   Variable x is 3. The switch checks cases 1, then 2 or 3, then default.

2. Step 2: Match case

   Case 2, 3 matches because x is 3, so it prints "Two or Three".

3. Final Answer:

   Two or Three -> Option C

4. Quick Check:

   3 matches case 2,3 [OK]

Hint: Check all case values including multiple ones [OK]

Common Mistakes:

• Ignoring multiple values in one case
• Choosing default instead of matching case
• Assuming case 3 is separate from case 2

4. Identify the error in this Go switch code:

package main
import "fmt"
func main() {
  x := 5
  switch {
  case x == 1:
    fmt.Println("One")
  case x == 5:
    fmt.Println("Five")
  case x == 10:
    fmt.Println("Ten")
  }
}

medium

A. No error; code runs and prints "Five"

B. Switch expression is missing a value but cases use conditions

C. Missing default case causes error

D. Case statements must be constants, not conditions

Solution

1. Step 1: Understand switch without expression

   Switch without a value allows cases to be conditions (boolean expressions).

2. Step 2: Check cases and output

   x is 5, so case x == 5 is true, printing "Five". No error occurs.

3. Final Answer:

   No error; code runs and prints "Five" -> Option A

4. Quick Check:

   Switch without value uses conditions [OK]

Hint: Switch without value uses boolean cases [OK]

Common Mistakes:

• Thinking default is mandatory
• Assuming switch must have a value
• Believing case conditions are invalid

5. Given this Go code, what will be printed?

package main
import "fmt"
func main() {
  score := 75
  switch {
  case score >= 90:
    fmt.Println("Grade A")
  case score >= 80:
    fmt.Println("Grade B")
  case score >= 70:
    fmt.Println("Grade C")
  default:
    fmt.Println("Fail")
  }
}

hard

A. Grade C

B. Grade B

C. Fail

D. Grade A

Solution

1. Step 1: Analyze switch without expression

   Switch uses conditions in cases, evaluated top to bottom.

2. Step 2: Evaluate conditions for score = 75

   score >= 90 is false, score >= 80 is false, score >= 70 is true, so prints "Grade C" and stops.

3. Final Answer:

   Grade C -> Option A

4. Quick Check:

   First true case runs, here score >= 70 [OK]

Hint: Switch stops at first true condition [OK]

Common Mistakes:

• Ignoring order of cases
• Assuming all true cases print
• Confusing >= with >