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# 附录 C：
在[语句与表达式](https://course.rs/basic/base-type/statement-expression.html)章节中，我们对表达式有过介绍，下面对这些常用表达式进行一一说明。
### 基本表达式
```rust
let n = 3 ;
let s = "test" ;
```
### if 表达式
```rust
fn main () {
let var1 = 10 ;
let var2 = if var1 >= 10 {
var1
} else {
var1 + 10
};
println! ( "{}" , var2 );
}
```
通过 `if` 表达式将值赋予 `var2` 。
你还可以在循环中结合 `continue` 、`break` 来使用：
```rust
let mut v = 0 ;
for i in 1 .. 10 {
v = if i == 9 {
continue
} else {
i
}
}
println! ( "{}" , v );
```
### if let 表达式
```rust
let o = Some ( 3 );
let v = if let Some ( x ) = o {
x
} else {
0
};
```
### match 表达式
```rust
let o = Some ( 3 );
let v = match o {
Some ( x ) => x ,
_ => 0
};
```
### loop 表达式
```rust
let mut n = 0 ;
let v = loop {
if n == 10 {
break n
}
n += 1 ;
};
```
### 语句块 {}
```rust
let mut n = 0 ;
let v = {
println! ( "before: {}" , n );
n += 1 ;
println! ( "after: {}" , n );
n
};
println! ( "{}" , v );
```
