Let for constants (immutable) in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the let keyword do in Swift?

The let keyword declares a constant, which means its value cannot be changed after it is set.

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What happens if you try to change a let constant after it is set?

Swift will give a compile-time error because constants cannot be modified once assigned.

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How do let and var differ in Swift?

let declares a constant (immutable), while var declares a variable (mutable).

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Example: <br><code>let pi = 3.14</code><br>Can you change <code>pi</code> later in the code?

No, because pi is declared with let, it is a constant and cannot be changed.

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Why use let instead of var when possible?

Using let helps prevent accidental changes and makes your code safer and easier to understand.

What keyword declares an immutable value in Swift?

A let

B var

C const

D immutable

let declares a constant that cannot be changed.

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

A The program runs normally

B The value changes silently

C Runtime error

D Compile-time error

Swift prevents changing constants by giving a compile-time error.

Which keyword allows you to change the value after declaration?

A var

B const

C let

D final

var declares a variable that can be changed.

Why is it good to use let when possible?

A To make code faster

B To prevent accidental changes

C To allow changes later

D To save memory

Using let helps keep values safe from accidental changes.

Which of these is a correct constant declaration in Swift?

A immutable name = "Alice"

B var name = "Alice"

C let name = "Alice"

D const name = "Alice"

let name = "Alice" correctly declares a constant.

Explain what let does in Swift and why it is useful.

Think about how constants help avoid mistakes.

Describe the difference between let and var in Swift.

One can change, the other cannot.