go 学习2【基本语法】

1.go的基本数据类型有

bool
string
int  int8  int16  int32  int64
uint uint8 uint16 uint32 uint64 uintptr
byte // alias for uint8
rune // alias for int32
     // represents a Unicode code point
float32 float64
complex64 complex128

2. 相关代码

package main

import (
	"fmt"
    "math/cmplx"
    "math"
)
// int default 0
var (
    ToBe   bool       = false
    MaxInt uint64     = 1<<64 - 1
    z      complex128 = cmplx.Sqrt(-5 + 12i)
)

const (
    Big   = 1 << 100                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
    Small = Big >> 99
)

type Point struct {
    X int
    Y int
}


// change bigger
func needInt(x int) int {
	return x*10 + 1 
}
// change smaller
func needFloat(x float64) float64 {
    return x * 0.1
}

func main() {
	// parameters can be used as varaibles
	fmt.Print("5+3 and 5-3 return : ")
	fmt.Println(xySumSub(5,3))

	// data type
	const f = "type:%T, value:%v\n"
    fmt.Printf(f, ToBe, ToBe)
    fmt.Printf(f, MaxInt, MaxInt)
    fmt.Printf(f, z, z)

    // truncate pi to intefer:
    pi := math.Pi
    fmt.Println(int(pi),int(pi+0.5),float32(3),math.Sqrt(1.414))
    fmt.Println(pi)

    // An untyped constant takes the type needed by its context.
    fmt.Println(needInt(Small))
    fmt.Println(needFloat(Small))
    fmt.Println(needFloat(Big))

    // math
    fmt.Println("2^3",math.Pow(2,3))
    fmt.Println("10%%3, 10/3",10%3,10/3)  // this is the same as c language

    // struct : most grammer is the same as c language
    point := Point{1,2}
    q := &point
    point.X = 10
    moveLeft(point,1)
    moveRight(q,100)
    q.Y = 0
    fmt.Println("point:",point)
    newPoint := new(Point)
    fmt.Println(newPoint)

    // array slice
    p := []int{2, 3, 5, 7, 11, 13}
    fmt.Println("p ==", p)
    fmt.Println("p[1:4] ==", p[1:4])
    // missing low index implies 0
    fmt.Println("p[:3] ==", p[:3])
    // missing high index implies len(s)
    fmt.Println("p[4:] ==", p[4:])
    // attention: array has length and capacity
    a := make([]int, 5)
    printSlice("a", a)
    b := make([]int, 0, 5)
    printSlice("b", b)
    c := b[:2]
    printSlice("c", c)
    d := c[2:5]
    printSlice("d", d)

    arrayT := new([2][4]int)
    arrayT[0][1] = 3
    arrayT[1][1] = 5
    fmt.Println("length of arrayT : ",len(arrayT))
    fmt.Println("length of arrayT[0] : ", len(arrayT[0]))
    for _,v := range arrayT {
    	for j := range v {
    		fmt.Printf("%d ",v[j])
    	}
    	fmt.Println()
    }

    arrayT2 := make([][]int,3,6) // create the first layer of the array
    for i := 0; i < 3; i++ {
    	arrayT2[i] = make([]int,5,5)// create the second layer of the array
    }

    for i:=0; i<3; i++ {
    	for j:=0; j<5; j++ {
    		fmt.Print(arrayT2[i][j]," ")
    	}
    	fmt.Println()
    }


}

func xySumSub(x,y int) (sum, sub int){
	sum = x + y
	sub = x - y
	return
}

func moveLeft(point Point,step int) {
	point.X -= step
}

func moveRight(point *Point,step int) {
	point.X += step
}

func printSlice(s string, x []int) {
    fmt.Printf("%s len=%d cap=%d %v\n",
        s, len(x), cap(x), x)
}