Switch from f64 to f32
Switch from f64 to f32

aakloxu/rust-by-example-cn,jinyuanxie/rust-by-example-cn,jinyuanxie/rust-by-example-cn,aakloxu/rust-by-example-cn,rust-lang-cn/rust-by-example-cn,rust-lang-cn/rust-by-example-cn