Summary - Control flow

Combine if, match and loops to build a number guessing game.

Control flow summary

Decisions: if/else if/else (bool condition, produces a value as an expression) and match (exhaustive, range and | patterns). Loops: loop (unconditional, break value), while (conditional), for (iterators, ../..=, enumerate, rev). Flow: break, continue, labels ('dis).

for n in 1..=15 {
    let s = match (n % 3, n % 5) {
        (0, 0) => "FizzBuzz".to_string(),
        (0, _) => "Fizz".to_string(),
        (_, 0) => "Buzz".to_string(),
        _ => n.to_string(),
    };
    print!("{s} ");
}

match on a tuple

Matching several values at once by putting them in a tuple is a readable approach. _ ignores the value at that position:

match (gun_tatil, hava_guzel) {
    (true, true) => "pikniğe git",
    (true, false) => "film izle",
    (false, _) => "işe git",
}

Exercise FizzBuzz

For the numbers 1 to 15, print FizzBuzz using match (n % 3, n % 5) on a tuple; print the values on one line separated by spaces (print!) and call println!() at the end.

Show example solution

fn main() {
    for n in 1..=15 {
        let s = match (n % 3, n % 5) {
            (0, 0) => "FizzBuzz".to_string(),
            (0, _) => "Fizz".to_string(),
            (_, 0) => "Buzz".to_string(),
            _ => n.to_string(),
        };
        print!("{s} ");
    }
    println!();
}

Test yourself

In the FizzBuzz example, why is the <code>(0, 0)</code> arm first?
- match runs the first matching arm; if (0, _) came first, 15 would be "Fizz"
- Alphabetical order
- Rust requires it
- Order doesn't matter
Show answer

match runs the first matching arm; if (0, _) came first, 15 would be "Fizz" — Arms are tried from top to bottom; the most specific pattern goes on top.

Reverse range

for i in (1..=5).____() {
    print!("{i} ");  // 5 4 3 2 1
}

Show answer

for i in (1..=5).rev() {
    print!("{i} ");  // 5 4 3 2 1
}

Group summary

if

Two-way decision
match

Exhaustive decision
loop / while

Unconditional / conditional loop
for

Iterator loop

Next lesson: What is ownership?

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