Rust Tutorial : Variables

Rules for Naming a Variable

variables in Rust are associated with a specific data type
the data type determines

the size and layout of the variable's memory
the range of values that can be stored within that memory
the set of operations that can be performed on the variable

naming rules

the name of a variable can be composed of letters, digits, and the underscore character
name must begin with either a letter or an underscore
upper and lowercase letters are distinct because Rust is case-sensitive

Syntax

the data type is optional while declaring a variable
the data type is inferred from the value assigned to the variable

fn main() {
   let fees = 25_000;
   let salary:f64 = 35_000.00;
   println!("fees is {} and salary is {}",fees,salary);
}

Immutable

by default variables are immutable − read only
the variable's value cannot be changed once a value is bound to a variable name

fn main() {
   let fees = 25_000;
   println!("fees is {} ",fees);
   fees = 35_000;
   println!("fees changed is {}",fees);
}

compiler will raise an error due to re-assignment of immutable variable

Mutable

prefix the variable name with mut keyword to make it mutable

let mut variable_name = value;
let mut variable_name:dataType = value;
Let us understand this with an example

fn main() {
   let mut fees:i32 = 25_000;
   println!("fees is {} ",fees);
   fees = 35_000;
   println!("fees changed is {}",fees);
}

index