变量定义要求 ：Go 语言变量名由字母、数字、下划线组成，其中首个字符不能为数字
在描述变量定义之前，先描述下go 语言的结构
package main
import "fmt"
import "math"
func main() {
// 定义单一变量
var age =18
fmt.Println("my age is ",age)
}
输出：my age is 18
// 定义多个变量
var width,height int = 100,50
fmt.Println("width is ",width,"height is",height)
输出： width is 100 height is 50
var (
name = "zhangsan"
age = 18
job = "go"
salary int
)
fmt.Println(" his name is",name, "age is",age, "job is",job, "salary is",salary)
输出： his name is zhangsan age is 18 job is IT salary is 0
go 的简短声明
简短声明的要求， := 左边的变量都有初始值 ,否则报错 例如 assignment mismatch: 3 variable but 2 values
name,age,job := "zhangsan",18,"IT"
fmt.Println(name,age,job)
输出 ：zhangsan 18 IT
简短声明的语法要求 := 操作符的左边至少有一个变量是尚未声明的
x,y :=20,30
fmt.Println("x is",x,"y is ",y)
y,z := 40,50
fmt.Println("y is",y,"z is ",z)
正常输出：
x is 20 y is 30
y is 40 z is 50
x,y :=20,30
x,y := 40,58
fmt.Println("x is",x ,"y is",y)
报错 no new variables on left side of :=，左边并没有尚未声明的变量
