for-loop - 如何循环特定(可变)次数？

Question

这个问题可能看起来非常基础，但我很难弄清楚如何做。我有一个整数，我需要使用 for 循环来循环整数次。

首先，我尝试了——

fn main() {
    let number = 10; // Any value is ok
    for num in number {
        println!("success");
    }
}

这会打印出错误

error[E0277]: `{integer}` is not an iterator
 --> src/main.rs:3:16
  |
3 |     for num in number{
  |                ^^^^^^ `{integer}` is not an iterator
  |
  = help: the trait `std::iter::Iterator` is not implemented for `{integer}`
  = note: if you want to iterate between `start` until a value `end`, use the exclusive range syntax `start..end` or the inclusive range syntax `start..=end`
  = note: required by `std::iter::IntoIterator::into_iter`

接下来，我尝试了——

fn main() {
    let number = 10; // Any value is ok
    for num in number.iter() {
        println!("success");
    }
}

编译器说没有整数的方法迭代器

error[E0599]: no method named `iter` found for type `{integer}` in the current scope
 --> src/main.rs:3:23
  |
3 |     for num in number.iter() {
  |                       ^^^^

我应该怎么做？

Answer 1

这是因为您要告诉编译器 number 中包含的 num，其中 number 不是迭代器，也没有实现 iter ，而不是 range 0..number 中的 num，它是一个迭代器。

文档将 for 循环描述为:

for loop_variable in iterator {
    code()
}

将代码更改为:

fn main() {
    let number = 10; 
    for num in 0..number { // change it to get range
        println!("success");
    }
}

您还可以将其更改为:

fn main() {
    let number = 10; 
    for num in 1..=number { // inclusive range
        println!("success");
    }
}

或者:

fn main() {
    let number = 10; 
    for _ in 0..number { // where _ is a "throw away" variable
        println!("success");
    }
}

另见 for documentation