声明

Use the let keyword to declare a variable.

fn main() {
    let name = "wangenius";  // string type
    let rating_float = 4.5;                 // float type
    let ismale = true;          // boolean type
    let icon_char = '♥';                    //unicode character type

    println!("name is:{}",name);
    println!("rating on 5 is:{}",rating_float);
    println!("is growing :{}",ismale);
    println!("icon is:{}",icon_char);
 }

size	signed	unsigned
8 bit	i8	u8
16 bit	i16	u16
32 bit	i32(default)	u32
64 bit	i64	u64
128 bit	i128	u128
Arch	isize	usize

大小为 arch 的整数在 x86 计算机上为 32 位，在 x64 计算机上为 64 位。

浮点数

fn main() {
   let result = 10.00;        //f64 by default
   let interest:f32 = 8.35;
   let cost:f64 = 15000.600;  //double precision

   println!("result value is {}",result);
   println!("interest is {}",interest);
   println!("cost is {}",cost);
}

自动类型转换

Automatic Type Casting

Rust 中不允许自动类型转换。考虑以下代码片段。整数值被分配给浮点变量利息。

fn main() {
   let interest:f32 = 8;   // integer assigned to float variable
   println!("interest is {}",interest);
}

output

error[E0308]: mismatched types
   --> main.rs:2:22
   |
 2 | let interest:f32=8;
   |    ^ expected f32, found integral variable
   |
   = note: expected type `f32`
      found type `{integer}`
error: aborting due to previous error(s)

Number Separator

为了方便大数字的可读性，我们可以使用视觉分隔符 _ 下划线来分隔数字。即 50,000 可以写成 50_000 。下面的示例显示了这一点。Rust 还支持科学 E 符号，例如 1e6 ， 7.6e-4 。关联的类型是 f64 。

fn main() {
    // Integer addition
    println!("1 + 2 = {}", 1u32 + 2);

    // Integer subtraction
    println!("1 - 2 = {}", 1i32 - 2);
    // Scientific notation
    println!("1e4 is {}, -2.5e-3 is {}", 1e4, -2.5e-3);

    // Short-circuiting boolean logic
    println!("true AND false is {}", true && false);
    println!("true OR false is {}", true || false);
    println!("NOT true is {}", !true);

    // Bitwise operations
    println!("0011 AND 0101 is {:04b}", 0b0011u32 & 0b0101);
    println!("0011 OR 0101 is {:04b}", 0b0011u32 | 0b0101);
    println!("0011 XOR 0101 is {:04b}", 0b0011u32 ^ 0b0101);
    println!("1 << 5 is {}", 1u32 << 5);
    println!("0x80 >> 2 is 0x{:x}", 0x80u32 >> 2);

    // Use underscores to improve readability!
    println!("One million is written as {}", 1_000_000u32);
}