变量与类型

var name string = Alice  // 完整
var age int                // 零值：0
name2 := Bob             // 短声明（函数内）

package main
 
import "fmt"
 
func main() {
    var name string = "Alice"
    var age int
    city := "北京"
 
    age = 30
    fmt.Println(name, age, city)
    fmt.Printf("%T %T %T\n", name, age, city)
}

package main
 
import "fmt"
 
func main() {
    var b bool
    var s string
    var i int
    var f float64
    var by byte
    var r rune
 
    fmt.Printf("bool: %v\n", b)
    fmt.Printf("string: %q\n", s)
    fmt.Printf("int: %v\n", i)
    fmt.Printf("float: %v\n", f)
    fmt.Printf("byte: %v\n", by)
    fmt.Printf("rune: %v\n", r)
}

package main
 
import "fmt"
 
const Pi = 3.14159
const (
    StatusOK    = 200
    StatusError = 500
)
 
func main() {
    const x = 10
    var i int = x
    var f float64 = x
    fmt.Println(i, f)
    fmt.Println(StatusOK, StatusError)
}

package main
 
import (
    "fmt"
    "strconv"
)
 
func main() {
    var i int = 42
    f := float64(i)
    s := strconv.Itoa(i)
    n, _ := strconv.Atoi("123")
 
    fmt.Printf("%T %v\n", f, f)
    fmt.Printf("%T %v\n", s, s)
    fmt.Printf("%T %v\n", n, n)
}

package main
 
import "fmt"
 
func main() {
    c := 25.0
    f := c*9/5 + 32
    fmt.Printf("%.1fC = %.1fF\n", c, f)
}

// 任务：输入半径 r，输出圆面积
// 公式：Pi * r^2，保留 2 位
// 期望：r=5 -> 78.54
 
package main
 
import "fmt"
 
func main() {
    var r int = 5
    // 补全代码
}