目录
（一）loop，while , for 三种循环 ，三个返回关键字 continue , break , return
一，条件语句
（一） 四种条件语句的基础用法用法
//1.第一种用法 if else
let flag = true;
if flag {
println!("true");
} else {
println!("false")
}
//2.第二种用法 if else if else
let num = 3;
if num==1 {
println!("1");
} else if flag && num ==2 {
println!("2");
} else {
println!("3");
}
//3.第三种用法 if可以具有返回值,多个分支中的返回值类型必须一致
let num = if flag {
1 //后面不允许跟;
} else {
2
};
println!("{:?}",num);
//4.rust管这叫匹配，不过我真心觉得这货是swith
let x = 5;
match x {
1 => println!("one"),
2 => println!("two"),
3 => println!("three"),
4 => println!("four"),
5 => println!("five"),
_ => println!("something else")//默认是必须的
}
（二）if let 和 while let 条件语句
// if let 表达式的缺点在于其穷尽性没有为编译器所检查，而 match 表达式则检查了。
// 如果去掉最后的 else 块而遗漏处理一些情况，编译器也不会警告这类可能的逻辑错误。
let mut num ;
let color: Option<&str> = None;
if let Some(cl) = color {
num =1;
} else if 1==1 {
num =2;
} else {
num =3;
}
//返回值不加 ;
let bool1 = true;
let num = if bool1 {
6
} else {
7
};
// while let 条件循环
let mut list = Vec::new();
list.push(1);
list.push(2);
while let Some(top) = list.pop() {
println!("{}", top);
}
二，循环
（一）loop，while , for 三种循环 ，三个返回关键字 continue , break , return
fn main() {
loop_f();//可以用死循环 loop
while_f();//可以用死循环 while (true)
for_f();
}
fn loop_f(){
let mut num = 1;
let m = loop {
num +=1;
if num == 2 {
println!("loop_f num= {}",num);
continue;
}else if num == 3 {
break num*10;
}
};
println!("loop_f num= {} , m = {}",num, m);
}
fn while_f(){
let mut num = 1;
while num!=2 {
num+=1;
println!("while_f num = {}",num)
}
}
fn for_f(){
let array = [6,7,8];
let mut i = 0;
//.iter()// 正循环 .rev() //反循环
for num in array.iter() {
i+=1;
if i == 2 {
return;
}
println!("for_f num = {}", num );
}
//或者这样,给出一个含有这之间值得迭代器。当然它不包括上限值array.len(), 0,1...array.len()-1
for num in 0..array.len() {
if num == 2 {
return;
}
println!("for_f num = {}", num );
}
}（二）for动态修改数组的值
let mut array = [6,7,8];
for num in 0..array.len() {
array[num] = array[num]+1;
}
println!("for_f num = {:?}", array );
console:
for_f num = [7, 8, 9]（三）得到数组的下标
//我们需要知道当前元素的下标，这样显然比较费劲,rust 提供了enumerate 函数
let mut array = [6,7,8];
let mut j = 0;
for i in array.iter(){
println!("i = {} and j = {}", i, j);
j=j+1;
}
println!("array enumerate");
for (i, &j) in array.iter().enumerate() {
println!("i = {} and j = {}", i, j);
}
println!("() enumerate");
for (i,j) in (5..7).enumerate() {
println!("i = {} and j = {}", i, j);
}
console:
i = 6 and j = 0
i = 7 and j = 1
i = 8 and j = 2
array enumerate
i = 0 and j = 6
i = 1 and j = 7
i = 2 and j = 8
() enumerate
i = 0 and j = 5
i = 1 and j = 6
（四）跳出多重循环
逻辑和使用循环标签（Loop labels）
使用循环标签 continue 相当于 break， break相当于 return。不过标签在特殊情况下更灵活
fn one(){
'outer: for x in 0..4 {
println!(" one x: {}",x);
for y in 0..4 {
if x==2 && y==2 {
println!(" one x: {}, y: {}", x, y);
continue 'outer;
}
}
}
}
fn two(){
for x in 0..4 {
println!(" two x: {}",x);
for y in 0..4 {
if x==2 && y==2 {
println!(" two x: {}, y: {}", x, y);
break ;
}
}
}
}
fn three(){
for x in 0..4 {
println!(" three x: {}",x);
for y in 0..4 {
if x==2 && y==2 {
println!(" three x: {}, y: {}", x, y);
return ;
}
}
}
}
fn four(){
'outer: for x in 0..4 {
println!(" four x: {}",x);
for y in 0..4 {
if x==2 && y==2 {
println!(" four x: {}, y: {}", x, y);
break 'outer;
}
}
}
}
console:
one x: 0
one x: 1
one x: 2
one x: 2, y: 2
one x: 3
two x: 0
two x: 1
two x: 2
two x: 2, y: 2
two x: 3
three x: 0
three x: 1
three x: 2
three x: 2, y: 2
four x: 0
four x: 1
four x: 2
four x: 2, y: 2