Short variable declaration in Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is short variable declaration in Go?

It is a way to declare and initialize a variable in one step using := instead of var and =.

beginner

How do you declare a variable named count with value 10 using short variable declaration?

You write count := 10. This creates and sets count to 10.

intermediate

Can you use short variable declaration outside functions in Go?

No, short variable declaration (:=) can only be used inside functions, not at package level.

intermediate

What happens if you use := with a variable name that already exists in the same scope?

If at least one new variable is declared, it reuses existing variables and declares new ones. If none are new, it causes a compile error.

beginner

Why is short variable declaration useful?

It makes code shorter and easier to read by combining declaration and initialization in one step.

Which symbol is used for short variable declaration in Go?

A ->

B =

C :=

D ==

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

Where can you use short variable declaration in Go?

A At package level only

B Inside functions only

C Anywhere in the code

D Only in main function

Short variable declaration is allowed only inside functions, not at package level.

What happens if you write x := 5 when x already exists in the same scope?

A It causes a compile error if no new variables are declared

B It declares a new variable x and shadows the old one

C It updates the value of x

D It ignores the statement

If no new variables are declared with :=, Go throws a compile error.

Which of these is a correct short variable declaration?

A a = 10

B var a := 10

C a =: 10

D a := 10

The correct syntax is a := 10 without the var keyword.

Why might you prefer short variable declaration over var with = ?

A It combines declaration and initialization in one step

B It is longer but clearer

C It works outside functions

D It allows redeclaring variables globally

Short variable declaration is concise and combines declaration and initialization.

Explain how short variable declaration works in Go and when you can use it.

Think about where you write := and what it does.

Describe what happens if you try to use := with only existing variables in the same scope.

Consider Go's rules for redeclaring variables with :=

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