Variable declaration using var in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of variable declaration with var and default value

What is the output of this Go program?

Go

package main
import "fmt"
func main() {
    var x int
    fmt.Println(x)
}

A undefined

B nil

C 0

D 1

💡 Hint

Variables declared with var get a default zero value.

In Go, when you declare a variable with var but do not assign a value, it gets the zero value for its type. For int, the zero value is 0.

❓ Predict Output

intermediate

Output of multiple variable declaration using var

What will this Go program print?

Go

package main
import "fmt"
func main() {
    var a, b, c = 1, "hello", true
    fmt.Println(a, b, c)
}

A 1 0 true

B 1 hello true

C 0 hello false

D Compilation error

💡 Hint

var can declare multiple variables with initial values.

Variables a, b, c are declared with values 1, "hello", and true respectively, so printing them shows those values.

❓ Predict Output

advanced

Output of var declaration with explicit type and no initial value

What is the output of this Go program?

Go

package main
import "fmt"
func main() {
    var flag bool
    fmt.Println(flag)
}

A false

B true

C nil

D Compilation error

💡 Hint

Boolean variables default to false if not initialized.

The zero value for bool type in Go is false, so flag prints false.

❓ Predict Output

advanced

Output of var declaration with short variable declaration inside function

What will this Go program print?

Go

package main
import "fmt"
func main() {
    var x int = 10
    y := 20
    fmt.Println(x + y)
}

A 30

B 1020

C Compilation error

D 0

💡 Hint

The + operator adds integers.

x is 10 and y is 20, so x + y equals 30.

🧠 Conceptual

expert

Error caused by var declaration with conflicting types

What error will this Go code produce?

Go

package main
func main() {
    var x int = 5
    var x string = "hello"
}

A no error, compiles fine

B type mismatch error

C syntax error: missing semicolon

D cannot redeclare x

💡 Hint

You cannot declare two variables with the same name in the same scope.

The code tries to declare x twice in the same scope, which causes a redeclaration error.

Practice

1. What does the var keyword do in Go?

easy

A. Starts a loop

B. Creates a function

C. Imports a package

D. Declares a variable with a name and type

Solution

1. Step 1: Understand the role of var

   The var keyword is used to declare variables in Go, giving them a name and a type.

2. Step 2: Differentiate from other keywords

   Other keywords like func, import, and for serve different purposes, not variable declaration.

3. Final Answer:

   Declares a variable with a name and type -> Option D

4. Quick Check:

   var declares variables [OK]

Hint: Remember: var means variable declaration [OK]

Common Mistakes:

• Confusing var with func or import
• Thinking var creates loops
• Assuming var is for constants

2. Which of the following is the correct way to declare an integer variable named count using var in Go?

easy

A. var count int

B. var count = int

C. count var int

D. int var count

Solution

1. Step 1: Recall Go variable declaration syntax

   In Go, the correct syntax is var variableName type, so var count int is correct.

2. Step 2: Check other options for syntax errors

   Options A, C, and D do not follow Go's syntax rules for variable declaration.

3. Final Answer:

   var count int -> Option A

4. Quick Check:

   var name type = var count int [OK]

Hint: Use 'var name type' format for declaration [OK]

Common Mistakes:

• Placing var after variable name
• Using '=' without value
• Swapping type and var keywords

3. What will be the output of this Go program?

package main
import "fmt"
func main() {
    var x int = 10
    var y int
    y = 5
    fmt.Println(x + y)
}

medium

A. 5

B. 10

C. 15

D. 0

Solution

1. Step 1: Identify variable values

   Variable x is declared with value 10, y is declared then assigned 5.

2. Step 2: Calculate the sum printed

   The program prints x + y which is 10 + 5 = 15.

3. Final Answer:

   15 -> Option C

4. Quick Check:

   10 + 5 = 15 [OK]

Hint: Add assigned values of variables to find output [OK]

Common Mistakes:

• Assuming uninitialized y is zero without assignment
• Confusing variable declaration with initialization
• Ignoring the assignment to y

4. Find the error in this Go code snippet:

package main
func main() {
    var name string = "Go"
    var age
    age = 10
}

medium

A. Missing type for variable 'age' in declaration

B. Cannot assign value after declaration

C. String value assigned to integer variable

D. Variable 'name' declared incorrectly

Solution

1. Step 1: Check variable declarations

   The variable age is declared without a type or initial value, which is invalid in Go.

2. Step 2: Understand Go's requirement for var declarations

   Go requires a type or an initial value when using var. Here, age has neither.

3. Final Answer:

   Missing type for variable 'age' in declaration -> Option A

4. Quick Check:

   var needs type or value [OK]

Hint: Always specify type or initial value with var [OK]

Common Mistakes:

• Declaring var without type or value
• Assuming assignment after declaration fixes type
• Confusing var with := shorthand

5. You want to declare two variables, a as an integer with value 5 and b as a string with value "hello", using var. Which is the correct way to do this in Go?

hard

A. var a, b int = 5, "hello"

B. var a int = 5; var b string = "hello"

C. var a = 5, b = "hello"

D. var a int, b string = "hello", 5

Solution

1. Step 1: Understand type declaration for multiple variables

   In Go, when declaring multiple variables with different types, each must be declared separately or with explicit types.

2. Step 2: Evaluate each option

   var a, b int = 5, "hello" tries to declare both as int but assigns a string to b, which is invalid. var a = 5, b = "hello" uses shorthand but mixes types without explicit declaration. var a int, b string = "hello", 5 mixes types incorrectly in one statement. var a int = 5; var b string = "hello" correctly declares each variable with its type and value.

3. Final Answer:

   var a int = 5; var b string = "hello" -> Option B

4. Quick Check:

   Separate var declarations for different types [OK]

Hint: Declare different types separately with var [OK]

Common Mistakes:

• Trying to declare different types in one var line
• Mixing types without explicit declaration
• Using shorthand := incorrectly with var