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Variables

Variables are containers for storing data values, like numbers and characters.

To create a variable in Rust, use the let keyword and specify the name of the variable ( name in this example):

Example

let name = "John";
println!("My first name is: {}", name);

Rust uses {} as a placeholder in println!() to show variable values.

In the example above, the output will be "My first name is: John".

You can use as many placeholders as you like:

Example

let name = "John";
let age = 30;
println!("{} is {} years old.", name, age);

When you use many placeholders, the values you pass are used in the same order.

In the example above

Important: The order matters. If you switch the values, the output will change:

Example

let name = "John";
let age = 30;
println!("{} is {} years old.", age, name);
// Outputs 30 is John years old

By default, variables in Rust cannot be changed after they are created:

Runnable example

let x = 5;
x = 10; // Error
println!("{}", x);

If you want to change the value of a variable, you must use the mut keyword (which means mutable/changeable):

Example

let mut x = 5;
println!("Before: {}", x);
x = 10;
println!("After: {}", x);