Flash cards
Review the key moves
What is the main idea behind Rust Loops?
Lesson checks
Practice each idea before moving on
Short Mimo-style checks built from this lesson's code, terms, and sequence.
Which statement best captures the main point of this lesson?
Complete the missing token from the example code.
___!("This will repeat forever!");Put the learning moves in the order that makes the concept easiest to apply.
Loops
Loops can execute a block of code as long as a specified condition is reached.
Loops are handy because they save time, reduce errors, and they make code more readable. For example, instead of writing the same line 10 times to print some text, you can use a loop to repeat it for you.
Rust has three types of loops: loop , while , and for .
loop
loop is the simplest of Rust's three loop types.
It will run forever unless you tell it to stop:
loop {
println!("This will repeat forever!");
}Warning
This loop never stops! You will need to press Ctrl + C to end the program.
To stop a loop, use the break keyword:
Example
let mut count = 1;
loop {
println!("Hello World!");
if count == 3 {
break;
}
count += 1;
}Example explained
- This prints "Hello World!" 3 times.
- It uses a counter to keep track of how many times it has looped.
- The counter starts at 1 ( let mut count = 1; ).
- Each time the loop runs, the counter goes up by 1: ( count += 1; ).
- When it reaches 3, the loop stops.
Return a Value
You can also return a value from a loop using break with a value.
This lets you save the result of the loop into a variable:
Example
let mut count = 1;
let result = loop {
println!("Hello!");
if count == 3 {
break count; // Stop the loop
and return the number 3
}
count += 1;
};
println!("The loop stopped at: {}", result);This loop prints "Hello!" until count reaches 3, then stops and returns that number.
Note
When you save the result of a loop into a variable, you must put a semicolon ( ; ) at the end.