Variable declaration using var in Go - Mini Project: Build & Apply

Variable declaration using var

📖 Scenario: Imagine you are organizing a small store's inventory. You want to keep track of the number of apples you have.

🎯 Goal: You will declare a variable using var to store the number of apples and then display it.

📋 What You'll Learn

Declare a variable called apples using var

Set the value of apples to 10

Print the value of apples

💡 Why This Matters

🌍 Real World

Declaring variables is the first step in storing and managing data in any program, like keeping track of inventory in a store.

💼 Career

Understanding variable declaration is essential for all programming jobs, as it helps in writing clear and maintainable code.

1

Declare the variable

Declare a variable called apples using var and set it to 10.

Go

package main

func main() {
    // Declare variable apples using var and set to 10
    // Your code here
}

Hint

Use var apples int = 10 to declare and set the variable.

2

Add a helper variable

Declare a variable called storeName using var and set it to "Fruit Shop".

Go

package main

func main() {
    var apples int = 10
    // Declare variable storeName using var and set to "Fruit Shop"
    // Your code here
}

Hint

Use var storeName string = "Fruit Shop" to declare the store name.

3

Use the variables

Use fmt.Println to print the message: "We have 10 apples in Fruit Shop" by combining apples and storeName. Use fmt.Printf with formatting.

Go

package main

import "fmt"

func main() {
    var apples int = 10
    var storeName string = "Fruit Shop"
    // Print the message using fmt.Printf
    // Your code here
}

Hint

Use fmt.Printf("We have %d apples in %s\n", apples, storeName) to print the message.

4

Display the result

Run the program and print the output message exactly as: We have 10 apples in Fruit Shop.

Go

package main

import "fmt"

func main() {
    var apples int = 10
    var storeName string = "Fruit Shop"
    fmt.Printf("We have %d apples in %s\n", apples, storeName)
    // Your code here
}

Hint

Make sure your program prints exactly: We have 10 apples in Fruit Shop

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