Rust Loops

Rust, in addition to flexible conditional statements, also has a mature design of loop structures. This should be felt by experienced developers.

while loop

The while loop is the most typical conditional statement loop：

fn main() {
　　　　let　mut　number　=　1;　
　　　　while　number　!=　4　　
　　　　　　　　println!("{}",　number);　
　　　　　　　　number　+=　1;　
　　　　}　
　　　　println!("EXIT");　
}

Running Result:

1
2
3
EXIT

Rust language has not had do up to the date of this tutorial.-The usage of while, but do is specified as a reserved word, which may be used in future versions.

In C Language, the for loop uses ternary statements to control the loop, but in Rust there is no such usage, and it needs to be replaced with a while loop：

int　i;　
for　(i　=　0;　i　<　10;　i++)　{　
　　　　//　Loop body
}

let mut i = 0;　
while　i　<　10　　
　　　　//　Loop body　
　　　　i　+=　1;　
}

for loop

The for loop is the most commonly used loop structure, often used to traverse a linear data structure (such as an array). The for loop traverses an array：

fn main() {　
　　　　10　2　3　4　5　
　　　　for　i　in　a.iter()　{　
　　　　　　　　println!("The value is　:　{}",　i);　
　　　　}　
}

Running Result:

The value is　:　10
The value is　:　20
The value is　:　30
The value is　:　40
The value is　:　50

fn main() {　
10　2　3　4　5　
　　　　5　　
　　　　　　　　println!("a[{}] = {}　
　　　　}　
}

Running Result:

a[0] =　10
a[1] =　20
a[2] =　30
a[3] =　40
a[4] =　50

Loop Loop

Experienced developers have certainly encountered several situations where a loop cannot determine whether to continue the loop at the beginning and end, and must control the loop at some point in the loop body. If faced with such a situation, we often implement the operation of exiting the loop in the middle of a while (true) loop body.

Rust has a native infinite loop structure called loop:

fn main() {　
　　　　let s = ['R', 'U', 'N', 'O', 'O', 'B'];　
　　　　let mut i = 0;　
　　　　loop {　
　　　　　　　　let ch = s[i];　
　　　　　　　　if ch == 'O' {　
　　　　　　　　　　　　break;　
　　　　　　　　}　
　　　　　　　　println!("'{}'", ch);
　　　　　　　　i　+=　1;　
　　　　}　
}

Running Result:

'R'　
'U'　
'N'

The loop loop can exit the entire loop and return a value to the outside by using the break keyword, similar to return. This is a very clever design, because loops like loop are often used as search tools, and of course, the result should be handed over if something is found:

fn main() {　
　　　　let s = ['R', 'U', 'N', 'O', 'O', 'B'];　
　　　　let mut i = 0;　
　　　　let location = loop {　
　　　　　　　　let ch = s[i];
　　　　　　　　if ch == 'O' {　
　　　　　　　　　　　　break i;　
　　　　　　　　}　
　　　　　　　　i　+=　1;　
　　　　};　
　　　　println!("The index of 'O' is {}", location);　
}

Running Result:

　The index of 'O' is　3