Golang 生成随机数

package main

import (
	"fmt"
	"math/rand"
	"time"
)

var (
	a  = 'a'
	b  = 'A'
	c  = '!'
	a1 string
	a2 string
	a3 string
)

func main() {
	//生成数值
	for i := 1; i <= 26; i++ {
		a1 += string(a)
		a++
		a2 += string(b)
		b++
		a3 += string(c)
		c++
	}
	a4 := a1 + a2 + a3
	bstring := []byte(a4)
	bstringlen := len(bstring)
	var str string
	//输入生成的个数
	var input int
	fmt.Printf("Please input number >>:")
	fmt.Scanln(&input)
	if input > bstringlen {
		fmt.Println("请输入小于", bstringlen)
		// panic("请输入小于", bstringlen)
	} else {
		//生成随机的for
		rand.Seed(time.Now().UnixNano())
		time.Sleep(time.Microsecond)
		for i := 1; i <= input; i++ {
			num := rand.Intn(bstringlen)
			//fmt.Println("NUM=", num)
			s := fmt.Sprintf("%c", bstring[num])
			str += s

		}
		fmt.Printf("生产的随机字符=%v\n", str)

	}

}