Increment & Decrement Operators in Rust in Rust

In programming, increasing the value of a variable by 1 is so common, there is an operator designed to do that.

That operator is the increment operator (+= 1):

let mut number: i32 = 10;
number += 1; // short for number = number + 1

println!("{}", number); // Output: 11

There is also one such operator for decreasing the value of a variable by 1.

That operator is the decrement operator (-= 1):

let mut number: i32 = 10;
number -= 1; // short for number = number - 1

println!("{}", number); // Output: 9

Postfix:

In the examples above, we have used these two operators in their postfix form, with operator (+= 1) after operand (number) such as number += 1.

If used postfix, the increment operator increments and returns the value before incrementing:

let mut number: i32 = 10;

let old_number = number;
number += 1;

println!("{}", old_number); // Output: 10
println!("{}", number); // Output: 11

This code first assigns the value of number (which is 10) to old_number and then increments number (making it 11). It's equivalent to this:

let old_number = number;
number += 1;

Prefix:

However, there is also the prefix form, with operator before operand (for example, number += 1).

When used prefix, the increment operator increments and returns the value after incrementing:

let mut number: i32 = 10;

number += 1;
let new_number = number;

println!("{}", new_number); // Output: 11
println!("{}", number); // Output: 11

This code first increments number (making it 11) and then assigns the new value of number to old_number (making it 11). It's equivalent to this:

number += 1;
let new_number = number;

Here's an example with the decrement operator:

let mut number: i32 = 10;

number -= 1;
let new_number = number;

println!("{}", new_number); // Output: 9
println!("{}", number); // Output: 9

Assignment
Follow the Coding Tutorial and let's practice with these operators!

Hint
Look at the examples above if you get stuck.