GO学习第四天（切片操作、map、rune）

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	arr := [...]int{0, 1, 2, 3, 4, 5, 6}
s1 := arr[2:5]
s3 := append(s1, 10)
s4 := append(s3, 20)
// 超过arr的cap 系统会重新分配更大数组
// s5 no longer view arr
s5 := append(s4, 30)
fmt.Println("s3,s4,s5=", s3, s4, s5)
s4[0] = 200
s3[1] = 600
s5[1] = 500
fmt.Println("s3,s4,s5=", s3, s4, s5)
fmt.Println("arr=", arr)

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func printSlice(s []int) {
fmt.Printf("%v,len=%d,cap=%dn", s, len(s), cap(s))
}
func main() {
var s []int
for i := 0; i < 50; i++ {
printSlice(s)
s = append(s, i*2)
}
s1 := []int{1, 2, 3}
printSlice(s1)
// 指定长度
s2 := make([]int, 15)
printSlice(s2)
// 指定len、cap
s3 := make([]int, 15, 60)
printSlice(s3)
}

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	fmt.Println("Copy slice:")
copy(s2, s1)
fmt.Println(s2)

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	fmt.Println("Popping slice element")
s2 = append(s2[:3], s2[4:]...)
fmt.Println(s2)
fmt.Println("Popping slice element from front")
front := s2[0]
s2 = s2[1:]
fmt.Println(front, s2)
fmt.Println("Popping slice element from back")
back := s2[len(s2)-1]
s2 = s2[:len(s2)-1]
fmt.Println(back, s2)

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	m1 := map[string]string{
"grade": "one",
}
var m2 map[string]int
// m2 == nil
m3 := make(map[string]int) // m3 == empty map
fmt.Println(m1, m2, m3)

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	for k, v := range m1 {
fmt.Println(k, v)
}

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	fmt.Println("Getting value")
// 存在ok true，不存在false
if name, ok := m1["grade"]; ok {
fmt.Println(name)
} else {
fmt.Println("key is not found.")
}

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	fmt.Println("Delete value")
name, ok := m1["grade"]
fmt.Println(name, ok)
delete(m1, "grade")
name, ok = m1["grade"]
fmt.Println(name, ok)

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// 中文三个字节，获得字节数
fmt.Println(len(str))
// 获得真正字数
fmt.Println(utf8.RuneCountInString(str))