If

• if is an expression.
• All if expressions start with the keyword if, followed by a condition.
• It’s also worth noting that the condition in this code must be a bool. If the condition isn’t a bool, we’ll get an error.
• Because if is an expression, we can use it on the right side of a let statement to assign the outcome to a variable
• Reference: Control Flow

if1.rs

fn bigger(a: i32, b: i32) -> i32 {
    // fill the function body using if expression
    if a > b {
        a
    } else {
        b
    }
}

fn main() {
    // You can optionally experiment here.
}

// Don't mind this for now :)
#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn ten_is_bigger_than_eight() {
        assert_eq!(10, bigger(10, 8));
    }

    #[test]
    fn fortytwo_is_bigger_than_thirtytwo() {
        assert_eq!(42, bigger(32, 42));
    }

    #[test]
    fn equal_numbers() {
        assert_eq!(42, bigger(42, 42));
    }
}

• This exercise is simple, we just need to add if expression that checks which variable is bigger in the function bigger.

  if a > b {
    a
  } else {
    b
  }

• Because if is an expression we can just type a and b and it will serve as returned value.

if2.rs

// TODO: Fix the compiler error on this function.
fn picky_eater(food: &str) -> &str {
    if food == "strawberry" {
        "Yummy!"
    } else if food == "potato" { // if potato return "I guess I can eat that."
        "I guess I can eat that."
    } else { // else return "No thanks!"
        "No thanks!"
    }
}

fn main() {
    // You can optionally experiment here.
}

// TODO: Read the tests to understand the desired behavior.
// Make all tests pass without changing them.
#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn yummy_food() {
        // This means that calling `picky_eater` with the argument "food" should return "Yummy!".
        assert_eq!(picky_eater("strawberry"), "Yummy!");
    }

    #[test]
    fn neutral_food() {
        assert_eq!(picky_eater("potato"), "I guess I can eat that.");
    }

    #[test]
    fn default_disliked_food() {
        assert_eq!(picky_eater("broccoli"), "No thanks!");
        assert_eq!(picky_eater("gummy bears"), "No thanks!");
        assert_eq!(picky_eater("literally anything"), "No thanks!");
    }
}

• In this example we need to take a look at the predefined testcases.
  • Test1 - yummy_food: : expect string "Yummy!" if the argument is "strawberry".
  • Test2 - neutral_food: expect string "I guess I can eat that." if the argument is "potato".
  • Test3 - default_disliked_food: expect string "broccoli", "gummy bears", or "literally anything".
• We are missing two case in the picky_eater function.
• So lets add potato using else if and the rest can go to else block.

if3.rs

fn animal_habitat(animal: &str) -> &str {
    // Make sure all returned values have the same types
    let identifier = if animal == "crab" {
        1
    } else if animal == "gopher" {
        2 // Don't return float
    } else if animal == "snake" {
        3
    } else {
        0 // Use 0 as substitute of unknown values
    };

    // Don't change the expression below!
    if identifier == 1 {
        "Beach"
    } else if identifier == 2 {
        "Burrow"
    } else if identifier == 3 {
        "Desert"
    } else {
        "Unknown"
    }
}

fn main() {
    // You can optionally experiment here.
}

// Don't change the tests!
#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn gopher_lives_in_burrow() {
        assert_eq!(animal_habitat("gopher"), "Burrow")
    }

    #[test]
    fn snake_lives_in_desert() {
        assert_eq!(animal_habitat("snake"), "Desert")
    }

    #[test]
    fn crab_lives_on_beach() {
        assert_eq!(animal_habitat("crab"), "Beach")
    }

    #[test]
    fn unknown_animal() {
        assert_eq!(animal_habitat("dinosaur"), "Unknown")
    }
}

• Because if is an expression, we can use it on the right side of a let statement to assign the outcome to a variable
• In this case we just need make sure that the returned values in the identifier if expression to have the same types.
• Make 0 as substitute of "unknown" value.