3. 变量

3.1 定义变量

package mainimport "fmt"// 全局变量可以不使用
var flg boolfunc main() {//局部变量定义后必须使用，默认零值var name int = 1fmt.Println(name)age := 1fmt.Println(age)//多变量定义，可以不同类型var s1, s2 = "s1", 2//可以更改赋值，但不能换类型s1 = "s2"fmt.Println(s1, s2)var (s3 = "s3"s4 int = 4s5 bool)fmt.Println(s3, s4, s5)
}

3.2 常量

package mainimport "fmt"func main() {const PI float32 = 3.14const (x int = 16y//y默认为16s = "abc"z//z默认为abc)fmt.Println(x, y, s, z)
}

3.3 iota

package mainimport "fmt"func main() {//iota自增const (err1 = iotaerr2 = iotaerr3 = iota)fmt.Println(err1, err2, err3) //0 1 2const (e1 = iotae2e3 = 100e4e5 = iotae6)fmt.Println(e1, e2, e3, e4, e5, e6) //0 1 100 100 4 5
}

3.4 匿名变量

package mainimport "fmt"func a() (int, bool) {return 0, false
}func main() {var _ intr1, _ := a()fmt.Println(r1) //0
}

4. 数据类型

4.3 类型转换

package mainimport ("fmt""strconv"
)func main() {//str->intvar strint = "12"myint, err := strconv.Atoi(strint)if err != nil {fmt.Println("convert error")}fmt.Println(myint)fmt.Println(strconv.Atoi(strint)) //12 <nil>//int->strvar intstr = 32fmt.Println(strconv.Itoa(intstr)) //32//str->float64myfloat, err := strconv.ParseFloat("3.14", 64)if err != nil {fmt.Println("convert error")}fmt.Println(myfloat) //-3.14//str->int(10进制)myint2, err := strconv.ParseInt("-42", 10, 64)if err != nil {fmt.Println("convert error")}fmt.Println(myint2) //-42//str->bool,0或"false"为false，1或"true"为true，其他数值报错mybool, err := strconv.ParseBool("0")if err != nil {fmt.Println("convert error")}fmt.Println(mybool) //falseboolstr := strconv.FormatBool(true)fmt.Println(boolstr) //truefloatstr := strconv.FormatFloat(3.1415, 'E', -1, 64)fmt.Println(floatstr) //3.1415E+00fmt.Println(strconv.FormatInt(-42, 16))//-2a
}

5. 字符串操作

5.4 输出

package mainimport ("fmt""strings"
)func main() {name := "neo"msg := fmt.Sprintf("用户：%s", name)fmt.Println(msg)var builder strings.Builderbuilder.WriteString("你好")builder.WriteString(name)re := builder.String()fmt.Println(re)
}

5.6 字符串函数

package mainimport ("fmt""strings"
)func main() {name := ",.hello,go."fmt.Println(strings.Contains(name, "go"))fmt.Println(strings.HasPrefix(name, "hello"))fmt.Println(strings.HasSuffix(name, "go"))fmt.Println(strings.Count(name, "o"))fmt.Println(strings.Index(name, "he"))fmt.Println(strings.Split(name, ","))fmt.Println(strings.Trim(name, ",."))//只剪除两边fmt.Println(strings.Replace(name, "go", "java", 2))
}

6. 条件控制

package mainimport "fmt"func main() {for i := 0; i < 3; i++ {fmt.Println(i)}name := "immocgo"for index, value := range name {fmt.Println(index, value)}age := 16if age < 18 {fmt.Println("child")} else if age == 18 {fmt.Println("18")} else {fmt.Println("adult")}switch age {case 18:fmt.Println("18")case 17, 16:fmt.Println("17,16")default:fmt.Println("default")}switch {case age == 18:fmt.Println("18")case age < 18:fmt.Println("child")default:fmt.Println("default")}
}