Why only if need some *i

help
1 
fn main() {
    let (mut initialEnergy, mut initialExperience) = (1, 1);
    let energy:Vec<i32> = vec![1,1,1,1];
    let experience:Vec<i32> = vec![1,1,1,50];

    let res = min_number_of_hours(initialEnergy, initialExperience, &energy, &experience);
    println!("res is: {}", res);
}

fn min_number_of_hours(initialEnergy:i32, mut initialExperience:i32, energy:&Vec<i32>, experience:&Vec<i32>) -> i32{
    let mut trainingHours = if initialEnergy > sum {0} else { sum - initialEnergy + 1 };
    for i in experience{
        if initialExperience > *i{
            initialExperience += i;
        }else {
            trainingHours += i - initialExperience + 1;
            initialExperience = 2 * i + 1;
        }
    }
    trainingHours
}
2

I've a hard time understanding your problem.

Do you want to know why you have to dereference i here (deduced by me from your title)?

3

I guess, the question was "Why I have to derefence in if condition only, while all the rest lines(e.g, initialExperience += i;) do not require manual dereferencing?"

4

Well, that'd be because i32 implements Add<&i32>, the trait that implements the logic for the + operator (and other traits implementing other mathematical operators like += and *, see std::ops module), but not PartialEq<&i32> (the trait used by comparison operators like >). Only PartialEq<i32> is implemented for i32. So you can add, add assign and multiply, etc. &i32 to a i32 value, but you can not compare &i32 with i32.

4 Likes
5

Thank you so much

1 Like