Switch expression behavior in Go - Mini Project: Build & Apply

Switch Expression Behavior in Go

📖 Scenario: You are building a simple program to identify the type of day based on a number. This is like checking the day of the week where numbers 1 to 7 represent Monday to Sunday.

🎯 Goal: Learn how to use a switch expression in Go to print the correct day name for a given number.

📋 What You'll Learn

Create a variable dayNumber with an integer value

Create a switch expression using dayNumber

Use case statements for numbers 1 to 7 with corresponding day names

Use default case to handle invalid numbers

Print the day name or an error message

💡 Why This Matters

🌍 Real World

Switch statements are used in many programs to choose actions based on user input or data values, like menus or commands.

💼 Career

Understanding switch expressions is important for writing clear and efficient decision-making code in Go, useful in backend development and system programming.

1

Create the day number variable

Create an integer variable called dayNumber and set it to 3.

Go

# Create the variable dayNumber and set it to 3
# Your code here

Hint

Use := to declare and assign the variable in one step.

2

Start the switch expression

Add a switch expression using the variable dayNumber inside the main function.

Go

package main

func main() {
    dayNumber := 3
    // Start a switch expression on dayNumber
    // Your code here
}

Hint

Write switch dayNumber { to start the switch expression.

3

Add cases for days 1 to 7 and default

Inside the switch dayNumber, add case statements for numbers 1 to 7. For each case, use fmt.Println to print the day name: "Monday" for 1, "Tuesday" for 2, "Wednesday" for 3, "Thursday" for 4, "Friday" for 5, "Saturday" for 6, and "Sunday" for 7. Add a default case that prints "Invalid day number".

Go

package main

import "fmt"

func main() {
    dayNumber := 3
    switch dayNumber {
        // Add cases 1 to 7 with fmt.Println for day names
        // Add default case for invalid day
        // Your code here
    }
}

Hint

Each case ends with a colon and the code to run is indented below it.

4

Run and print the output

Run the program and print the output. The program should print the day name for dayNumber = 3.

Go

package main

import "fmt"

func main() {
    dayNumber := 3
    switch dayNumber {
    case 1:
        fmt.Println("Monday")
    case 2:
        fmt.Println("Tuesday")
    case 3:
        fmt.Println("Wednesday")
    case 4:
        fmt.Println("Thursday")
    case 5:
        fmt.Println("Friday")
    case 6:
        fmt.Println("Saturday")
    case 7:
        fmt.Println("Sunday")
    default:
        fmt.Println("Invalid day number")
    }

    // Your code here
}

Hint

Run the program and check the output matches the expected day name.

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 >