Short variable declaration in Go - Mini Project: Build & Apply

Short Variable Declaration in Go

📖 Scenario: Imagine you are writing a simple Go program to store and display information about a fruit.

🎯 Goal: You will create variables using Go's short variable declaration syntax and print their values.

📋 What You'll Learn

Use short variable declaration to create variables

Use the exact variable names and values given

Print the variables to show their values

💡 Why This Matters

🌍 Real World

Short variable declaration is a common and concise way to create variables in Go programs, useful in many real-world applications like data processing and web development.

💼 Career

Understanding short variable declaration is essential for Go developers to write clean and efficient code, a skill valued in software engineering jobs.

1

Create variables using short variable declaration

Use Go's short variable declaration to create a variable fruit with the value "apple" and a variable quantity with the value 5.

Go

// Use short variable declaration to create fruit and quantity
// Your code here

Hint

Use := to declare and assign variables in one step.

2

Add a variable for price

Add a short variable declaration for a variable price with the value 0.99.

Go

package main

import "fmt"

func main() {
	fruit := "apple"
	quantity := 5
	// Declare price variable here
	// Your code here
}

Hint

Remember to use := for short variable declaration.

3

Calculate total cost

Create a new variable totalCost using short variable declaration that multiplies quantity and price.

Go

package main

import "fmt"

func main() {
	fruit := "apple"
	quantity := 5
	price := 0.99
	// Calculate totalCost here
	// Your code here
}

Hint

Convert quantity to float64 before multiplying with price.

4

Print the total cost

Use fmt.Printf to print the message: Total cost for 5 apples is $4.95 using the variables quantity, fruit, and totalCost. Format totalCost to two decimal places.

Go

package main

import "fmt"

func main() {
	fruit := "apple"
	quantity := 5
	price := 0.99
	totalCost := float64(quantity) * price
	// Print the total cost message
	// Your code here
}

Hint

Use fmt.Printf with %d for integers, %s for strings, and %.2f for floating numbers with two decimals.

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