Variable declaration using var in Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the var keyword do in Go?

It declares a variable with a specified type and optionally assigns it a value.

beginner

How do you declare an integer variable named age using var?

You write:

var age int

This creates a variable age of type int with a default value 0.

intermediate

Can you declare multiple variables at once using var? How?

Yes. Use parentheses and list variables:

var (
  x int
  y string
)

This declares x as int and y as string.

beginner

What is the default value of a variable declared with var but not assigned?

It depends on the type:
- Numbers: 0
- Strings: empty string
- Booleans: false
- Pointers: nil

beginner

How to declare and assign a variable in one line using var?

Write:

var name string = "Alice"

This declares name as string and assigns "Alice".

What is the correct way to declare a variable count of type int using var?

A var count int

B count := int

C int var count

D var int count

The correct syntax is var count int to declare an int variable.

What is the default value of a string variable declared with var but not assigned?

A nil

B empty string

C 0

D false

Strings default to an empty string "" when declared but not assigned.

Which of these declares multiple variables correctly?

A var x, y int

B var (x int, y string)

C var x int; y string

D var ( x int y string )

Both var x, y int and using parentheses with new lines: var ( x int y string ) are correct.

How do you declare and assign a variable name with value "Bob" using var?

A name := "Bob"

B var name = "Bob"

C var name string = "Bob"

D var string name = "Bob"

The full declaration with type and assignment is var name string = "Bob".

What happens if you declare a variable with var but do not assign a value?

A It keeps old memory value

B It causes an error

C It is nil always

D It has a zero value depending on type

Variables declared with var get a zero value based on their type automatically.

Explain how to declare a variable using var in Go and what happens if you don't assign a value.

Think about how Go handles variables when you only declare them.

Describe how to declare multiple variables at once using var and why it might be useful.

Consider grouping declarations for neatness.

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