Var for variables (mutable) in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a mutable variable named age with value 25.

Swift

var [1] = 25

Drag options to blanks, or click blank then click option'

Aage

Blet

Cconstant

Dnumber

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'let' instead of a variable name after 'var'.

Using a reserved keyword as the variable name.

In Swift, var declares a mutable variable. Here, age is the variable name.

2fill in blank

medium

Complete the code to change the value of the variable score to 100.

Swift

score [1] 100

Drag options to blanks, or click blank then click option'

Alet

B=

Cvar

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' which is a comparison operator.

Using 'let' or 'var' which are for declarations.

The = operator assigns a new value to a variable.

3fill in blank

hard

Fix the error in the code to declare a mutable variable name with value "Alice".

Swift

[1] name = "Alice"

Drag options to blanks, or click blank then click option'

Avar

Bvariable

Clet

Dconst

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'let' which declares a constant.

Using 'const' which is not a Swift keyword.

Use var to declare a mutable variable in Swift.

4fill in blank

hard

Fill both blanks to declare a mutable variable temperature with value 72.

Swift

[1] [2] = 72

Drag options to blanks, or click blank then click option'

Avar

Blet

Ctemperature

Dtemp

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'let' instead of 'var' for mutable variables.

Using a variable name that does not match the instruction.

var declares a mutable variable, and temperature is the variable name.

5fill in blank

hard

Fill all three blanks to declare a mutable variable count, assign 10, and then update it to 15.

Swift

[1] [2] = 10
[3] = 15

Drag options to blanks, or click blank then click option'

Avar

Bcount

Dlet

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'let' to declare a variable that is later changed.

Using different names for the variable in declaration and update.

First, var declares the variable, then count is the name. Later, count is updated to 15.

Practice

1. What does the var keyword do in Swift?

easy

A. It creates a variable whose value can change later.

B. It creates a constant value that cannot change.

C. It defines a function.

D. It declares a type alias.

Solution

1. Step 1: Understand the purpose of var

   The var keyword is used to declare variables that can be changed after they are set.

2. Step 2: Compare with constants

   Unlike let, which creates constants, var allows the value to be updated.

3. Final Answer:

   It creates a variable whose value can change later. -> Option A

4. Quick Check:

   var means mutable variable [OK]

Hint: Remember: var means variable, value can change [OK]

Common Mistakes:

• Confusing var with let (constant)
• Thinking var creates constants
• Mixing var with function declaration

2. Which of the following is the correct way to declare a mutable variable named score with initial value 10 in Swift?

easy

A. let score = 10

B. variable score = 10

C. const score = 10

D. var score = 10

Solution

1. Step 1: Identify the keyword for mutable variables

   In Swift, var declares a variable that can change, so use var score = 10.

2. Step 2: Check other options

   let creates a constant, variable and const are not valid Swift keywords.

3. Final Answer:

   var score = 10 -> Option D

4. Quick Check:

   Mutable variable uses var [OK]

Hint: Use var for variables, let for constants [OK]

Common Mistakes:

• Using let instead of var for mutable variables
• Using invalid keywords like variable or const
• Missing the equals sign

3. What will be the output of this Swift code?

var count = 5
count = 10
print(count)

medium

A. 10

B. 5

C. Error: Cannot assign to constant

D. nil

Solution

1. Step 1: Understand variable assignment

   The variable count is declared with var and initially set to 5, so it can be changed.

2. Step 2: Update and print value

   The value is changed to 10 before printing, so print(count) outputs 10.

3. Final Answer:

   10 -> Option A

4. Quick Check:

   Mutable var updates value correctly [OK]

Hint: var allows value change, so print updated value [OK]

Common Mistakes:

• Thinking var acts like let (constant)
• Expecting original value instead of updated
• Confusing syntax causing errors

4. Identify the error in this Swift code:

var name = "Alice"
name = 42
print(name)

medium

A. Syntax error on variable declaration

B. No error, prints 42

C. Type mismatch error when assigning 42 to name

D. Runtime error when printing

Solution

1. Step 1: Check variable type inference

   Variable name is inferred as String because of initial value "Alice".

2. Step 2: Assign incompatible type

   Assigning an integer 42 to a String variable causes a type mismatch error.

3. Final Answer:

   Type mismatch error when assigning 42 to name -> Option C

4. Quick Check:

   Swift variables keep type, cannot assign different type [OK]

Hint: Variable type fixed by first value, cannot assign different type [OK]

Common Mistakes:

• Ignoring type mismatch errors
• Thinking var allows any type changes
• Confusing syntax error with type error

5. You want to keep track of a player's score that changes during the game. Which Swift code correctly declares and updates this score using var?

1. let score = 0
2. score = 10

3. var score = 0
4. score = 10

5. var score: String
6. score = 10

7. let score: Int
8. score = 10

hard

A. Lines 1 and 2

B. Lines 3 and 4

C. Lines 5 and 6

D. Lines 7 and 8

Solution

1. Step 1: Identify mutable variable declaration

   Lines 3 and 4 declare score with var and assign 0, then update to 10, which is correct.

2. Step 2: Check other options

   Lines 1 and 2 use let (constant), so line 2 causes error. Lines 5 and 6 declare score as String but assign integer 10, causing type mismatch error. Lines 7 and 8 use let constant and then try to assign, causing error.

3. Final Answer:

   Lines 3 and 4 -> Option B

4. Quick Check:

   Use var to declare and update variables [OK]

Hint: Declare with var and assign before update [OK]

Common Mistakes:

• Using let for variables that change
• Type mismatch with wrong type annotation
• Confusing var and let usage