For Over Series

Sometimes when programming it's necessary to perform same or almost the same operation a couple of times.

To prevent writing the same thing over and over again we can use Loops.

The for loop has the following syntax

for element in range {
    code
}

A range expression defines how many times the loop should run, typically written as start..end (which runs from start to end-1) or start..=end (which runs from start to end, including end).

For example, a loop from 0 to 5 (not including):

for i in 0..5 {
    println!("{}", i);
}

It will execute the print statement 5 times:

0
1
2
3
4

Loops have many use cases. For example, let's sum all the numbers from 1 to 100:

let mut sum_numbers = 0;
for i in 1..=100 {
    sum_numbers += i;
}
println!("{}", sum_numbers);

This will first loop through all numbers between 1 to 100 (including 100 because of ..= sign) and sum all of them, then it will print the sum_numbers variable

If for some reason you want to create a loop without using a variable (i), you should add underscore at the start of the name: _i. This will tell the compiler that it is okay that it is not used, and it will prevent the program to produce a warning:

for _i in 0..5 {
    println!("Hello!");
}