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);
 }

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);
}

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);
}