Short variable declaration in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of short variable declaration with multiple variables

What is the output of this Go program?

Go

package main
import "fmt"
func main() {
    a, b := 5, 10
    a, b = b, a
    fmt.Println(a, b)
}

A 5 10

B 0 0

C 10 5

D Compilation error

💡 Hint

Remember that := declares and initializes variables, and you can swap values using multiple assignment.

The variables a and b are declared and initialized with 5 and 10. Then their values are swapped using a, b = b, a. So the output is 10 5.

❓ Predict Output

intermediate

Short variable declaration inside if statement

What will this Go program print?

Go

package main
import "fmt"
func main() {
    if x := 7; x > 5 {
        fmt.Println(x)
    } else {
        fmt.Println(0)
    }
}

A No output

B 0

C Compilation error

D 7

💡 Hint

The variable x is declared and initialized in the if statement condition.

The short variable declaration x := 7 happens inside the if statement. Since 7 > 5 is true, it prints 7.

❓ Predict Output

advanced

Short variable declaration with redeclaration and assignment

What is the output of this Go program?

Go

package main
import "fmt"
func main() {
    x := 10
    x, y := 20, 30
    fmt.Println(x, y)
}

A 10 30

B 20 30

C Compilation error

D 10 0

💡 Hint

Short variable declaration can redeclare variables if at least one new variable is declared.

The first line declares x=10. The second line redeclares x and declares y. x is updated to 20, y is 30. So output is 20 30.

❓ Predict Output

advanced

Short variable declaration with blank identifier

What will this Go program print?

Go

package main
import "fmt"
func main() {
    x, _ := 5, 10
    fmt.Println(x)
}

A 5

B 10

C 0

D Compilation error

💡 Hint

The blank identifier _ ignores the second value.

The variable x is assigned 5, the second value 10 is discarded using _. So printing x outputs 5.

🧠 Conceptual

expert

Short variable declaration behavior in nested scopes

Consider this Go code snippet. What is the value of x printed by the program?

Go

package main
import "fmt"
func main() {
    x := 1
    {
        x := 2
        {
            x := 3
            fmt.Println(x)
        }
    }
}

A 3

B 2

C 1

D Compilation error

💡 Hint

Each nested block can declare a new variable with the same name, shadowing outer ones.

Each block declares a new x. The innermost x is 3, so fmt.Println prints 3.

Practice

1. What does the short variable declaration := do in Go?

easy

A. It assigns a value to an already declared variable outside a function.

B. It declares and initializes a new variable inside a function.

C. It declares a variable without initializing it.

D. It declares a global variable accessible everywhere.

Solution

1. Step 1: Understand short variable declaration usage

   The := syntax declares and initializes a variable in one step inside functions.

2. Step 2: Differentiate from other declarations

   It cannot be used without initialization or outside functions for global variables.

3. Final Answer:

   It declares and initializes a new variable inside a function. -> Option B

4. Quick Check:

   Short declaration = declare + initialize [OK]

Hint: Remember := means declare and assign inside functions [OK]

Common Mistakes:

• Thinking := works outside functions
• Using := without initializing
• Confusing := with simple assignment =

2. Which of the following is the correct way to declare and initialize a variable using short variable declaration in Go?

easy

A. x =: 10

B. var x := 10

C. x := 10

D. x :== 10

Solution

1. Step 1: Identify correct short declaration syntax

   The correct syntax is variable := value without the var keyword.

2. Step 2: Check each option

   x := 10 matches the correct syntax. The other options have invalid syntax.

3. Final Answer:

   x := 10 -> Option C

4. Quick Check:

   Short declaration syntax = variable := value [OK]

Hint: Short declaration never uses 'var' keyword [OK]

Common Mistakes:

• Adding 'var' with :=
• Swapping := to =:
• Using double equals or colons

3. What will be the output of this Go code snippet?

func main() {
    a := 5
    a := 10
    fmt.Println(a)
}

medium

A. Compilation error

B. 10

C. 5

D. 0

Solution

1. Step 1: Analyze variable redeclaration

   Using a := 5 then a := 10 in the same scope causes redeclaration error.

2. Step 2: Understand Go's redeclaration rules

   Short declaration requires at least one new variable; here a is redeclared without new variables, causing error.

3. Final Answer:

   Compilation error -> Option A

4. Quick Check:

   Redeclaring same var with := in same scope = error [OK]

Hint: Short declaration needs at least one new variable [OK]

Common Mistakes:

• Assuming redeclaration overwrites variable
• Expecting last value to print
• Ignoring scope rules

4. Identify the error in this Go code snippet:

func main() {
    x := 10
    x := 20
    fmt.Println(x)
}

medium

A. x is redeclared in the same scope causing a compile error.

B. x is not initialized before use.

C. fmt.Println is used incorrectly.

D. No error, output will be 20.

Solution

1. Step 1: Check variable redeclaration

   The variable x is declared twice with := in the same function scope, which is not allowed.

2. Step 2: Understand Go's redeclaration rules

   Redeclaring a variable with := requires at least one new variable; here none is new, so compile error occurs.

3. Final Answer:

   x is redeclared in the same scope causing a compile error. -> Option A

4. Quick Check:

   Redeclaration without new vars = compile error [OK]

Hint: Redeclare only if at least one new variable appears [OK]

Common Mistakes:

• Thinking redeclaration updates variable silently
• Ignoring compile errors on redeclaration
• Assuming output prints last assigned value

5. Given the code below, which line correctly uses short variable declaration to add a new variable c while updating a?

func main() {
    a := 1
    b := 2
    // Insert line here
    fmt.Println(a, b, c)
}

hard

A. a, b := 3, 4

B. a := 3; c := 4

C. c := 4

D. a, c := 3, 4

Solution

1. Step 1: Understand short declaration with existing variables

   To update a and declare new c in one line, use a, c := 3, 4.

2. Step 2: Check other options

   a, b := 3, 4 redeclares two existing variables without a new one, causing a compile error. a := 3; c := 4 redeclares existing a without a new variable (compile error). c := 4 declares c without updating a.

3. Final Answer:

   a, c := 3, 4 -> Option D

4. Quick Check:

   Short declaration updates existing + new vars = correct [OK]

Hint: Use := with at least one new variable to update and declare [OK]

Common Mistakes:

• Trying to redeclare only existing vars with :=
• Declaring new vars separately without updating existing
• Forgetting to include new variable in declaration