Var for variables (mutable) in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Swift code using var?

Consider this Swift code snippet. What will it print?

Swift

var count = 5
count = 10
print(count)

A 10

B 5

C Compilation error

D Runtime error

💡 Hint

Remember, var allows the value to change.

The variable count is declared with var, so it can be changed from 5 to 10. The print statement outputs 10.

❓ Predict Output

intermediate

What happens if you try to change a let constant?

What error will this Swift code produce?

Swift

let name = "Alice"
name = "Bob"
print(name)

A Runtime error

B Compile-time error: Cannot assign to value: 'name' is a 'let' constant

C Prints Alice

D Prints Bob

💡 Hint

let means the value cannot be changed after assignment.

Since name is declared with let, trying to assign a new value causes a compile-time error.

🔧 Debug

advanced

Why does this code cause an error?

Examine this Swift code. Why does it fail to compile?

Swift

var number = 10
number = "ten"
print(number)

A Prints 10

B Runtime error: Invalid type conversion

C Prints "ten"

D Type mismatch error: Cannot assign String to Int variable

💡 Hint

Swift variables have fixed types once declared.

The variable number is declared as an Int. Assigning a String causes a type mismatch compile error.

🧠 Conceptual

advanced

What is the difference between var and let in Swift?

Choose the best explanation of the difference between var and let in Swift.

A <code>var</code> and <code>let</code> are interchangeable and have no difference.

B <code>var</code> declares a constant; <code>let</code> declares a mutable variable.

C <code>var</code> declares a mutable variable; <code>let</code> declares an immutable constant.

D <code>var</code> is used only for integers; <code>let</code> is used only for strings.

💡 Hint

Think about whether the value can change after assignment.

var allows the value to be changed later. let means the value cannot be changed once set.

❓ Predict Output

expert

What is the output of this Swift code with var and scope?

What will this Swift code print?

Swift

var x = 5
if true {
    var x = 10
    print(x)
}
print(x)

A

10
5

B

5
10

C

10
10

D

5
5

💡 Hint

Remember that variables declared inside a block have their own scope.

The inner var x = 10 shadows the outer x inside the if block. So first print outputs 10, then outside the block it prints 5.