Var for variables (mutable) in Swift - Cheat Sheet & Quick Revision

Recall & Review

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What does var mean in Swift?

var is used to declare a variable that can change its value later. It means the value is mutable.

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How do you declare a variable named score with the value 10 using var?

You write: var score = 10. This means score can be changed later.

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What happens if you try to change a variable declared with let instead of var?

let creates a constant, which means its value cannot change. Trying to change it causes an error.

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Why use var instead of let?

Use var when you want to change the value later, like a score in a game. Use let when the value stays the same.

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Example: What is the output of this code?<br>

var count = 5
count = 10
print(count)

The output is 10 because count was changed from 5 to 10.

Which keyword declares a variable that can change its value in Swift?

A const

B let

C var

D static

var declares a mutable variable. let declares a constant.

What happens if you try to assign a new value to a let constant?

A It changes successfully

B It causes a compile-time error

C It prints a warning but runs

D It converts to <code>var</code> automatically

let constants cannot be changed. Trying to do so causes an error.

Which of these is a correct way to declare a mutable variable name with value "Anna"?

A static name = "Anna"

B let name = "Anna"

C const name = "Anna"

D var name = "Anna"

var name = "Anna" declares a variable that can be changed later.

If you want a value to never change, which keyword should you use?

A let

B change

C mutable

D var

let creates a constant that cannot be changed.

What will this code print?<br>

var x = 3
x = 7
print(x)

A 7

B 3

C Error

D Nothing

The variable x is changed to 7, so it prints 7.

Explain the difference between var and let in Swift.

Think about whether the value can be changed after it is set.

Write a short Swift code snippet that shows how to declare a variable and change its value.

Start with var, then assign a new value, then print.