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);What is {} ?
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);Using Placeholders in Order
When you use many placeholders, the values you pass are used in the same order.
In the example above
- The first {} gets replaced with name ("John")
- The second {} gets replaced with age (30)
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 oldVariable Values Cannot be Changed by Default
By default, variables in Rust cannot be changed after they are created:
Runnable example
let x = 5;
x = 10; // Error
println!("{}", x);Change Variable Values
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);