You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: main.go
    path of file: ./repos/learning/golang/source_code/Go语言核心编程代码/chapter06/stringfunc
    
    the code of the file until where you have to start completion: package main
import (
	"fmt"
	"strconv"
	"strings"
)

func main(){

	//统计字符串的长度，按字节 len(str)
	////golang的编码统一为utf-8 (ascii的字符(字母和数字) 占一个字节，汉字占用3个字节)
	str := "hello北" 
	fmt.Println("str len=", len(str)) // 8


	str2 := "hello北京"
	//字符串遍历，同时处理有中文的问题 r := []rune(str)
	r := []rune(str2)
	for i := 0; i < len(r); i++ {
		fmt.Printf("字符=%c\n", r[i])
	}


	//字符串转整数:	 n, err := strconv.Atoi("12")
	n, err := strconv.Atoi("123")
	if err != nil {
		fmt.Println("转换错误", err)
	}else {
		fmt.Println("转成的结果是", n)
	}

	//4)整数转字符串  str = strconv.Itoa(12345)
	str = strconv.Itoa(12345)
	fmt.Printf("str=%v, str=%T\n", str, str)

	//5)字符串 转 []byte:  var bytes = []byte("hello go")
	var bytes = []byte("hello go")
	fmt.Printf("bytes=%v\n", bytes)

	//6)[]byte 转 字符串: str = string([]byte{97, 98, 99})
	str = string([]byte{97, 98, 99}) 
	fmt.Printf("str=%v\n", str)

	//10进制转 2, 8, 16进制:  str = strconv.FormatInt(123, 2),返回对应的字符串
	str = strconv.FormatInt(123, 2)
	fmt.Printf("123对应的二进制是=%v\n", str)
	str = strconv.FormatInt(123, 16)
	fmt.Printf("123对应的16进制是=%v\n", str)

	//查找子串是否在指定的字符串中: strings.Contains("seafood", "foo") //true
	b := strings.Contains("seafood", "mary")
	fmt.Printf("b=%v\n", b) 

	//统计一个字符串有几个指定的子串 ： strings.Count("ceheese", "e") //4
	num := strings.Count("ceheese", "e")
	fmt.Printf("num=%v\n", num)

	//10)不区分大小写的字符串比较(==是区分字母大小写的): fmt.Println(strings.EqualFold("abc", "Abc")) // true

	b = strings.EqualFold("abc", "Abc")
	fmt.Printf("b=%v\n", b) //true

	fmt.Println("结果","abc" == "Abc") // false //区分字母大小写

	//11)返回子串在字符串第一次出现的index值，如果没有返回-1 : 
	//strings.Index("NLT_abc", "abc") // 4

	index := strings.Index("NLT_abcabcabc", "abc") // 4
	fmt.Printf("index=%v\n",index)

	//12)返回子串在字符串最后一次出现的index，
	//如没有返回-1 : strings.LastIndex("go golang", "go")

	index = strings.LastIndex("go golang", "go") //3
	fmt.Printf("index=%v\n",index)

	//将指定的子串替换成 另外一个子串: strings.Replace("go go hello", "go", "go语言", n) 
	//n可以指定你希望替换几个，如果n=-1表示全部替换

	str2 = "go go hello"
	str = strings.Replace(str2, "go", "北京", -1)
	fmt.Printf("str=%v str2=%v\n", str, str2)

	//按照指定的某个字符，为分割标识，将一个字符串拆分成字符串数组： 
	//strings.Split("hello,wrold,ok", ",")
	strArr := strings.Split("hello,wrold,ok", ",")
	for i := 0; i < len(strArr); i++ {
		fmt.Printf("str[%v]=%v\n", i, strArr[i])
	} 
	fmt.Printf("strArr=%v\n", strArr)

	//15)将字符串的字母进行大小写的转换: 
	//strings.ToLower("Go") // go strings.ToUpper("Go") // GO

	str = "goLang Hello"
	str = strings.ToLower(str) 
	str = strings.ToUp
    
func main(){

	//统计字符串的长度，按字节 len(str)
	////golang的编码统一为utf-8 (ascii的字符(字母和数字) 占一个字节，汉字占用3个字节)
	str := "hello北" 
	fmt.Println("str len=", len(str)) // 8


	str2 := "hello北京"
	//字符串遍历，同时处理有中文的问题 r := []rune(str)
	r := []rune(str2)
	for i := 0; i < len(r); i++ {
		fmt.Printf("字符=%c\n", r[i])
	}


	//字符串转整数:	 n, err := strconv.Atoi("12")
	n, err := strconv.Atoi("123")
	if err != nil {
		fmt.Println("转换错误", err)
	}else {
		fmt.Println("转成的结果是", n)
	}

	//4)整数转字符串  str = strconv.Itoa(12345)
	str = strconv.Itoa(12345)
	fmt.Printf("str=%v, str=%T\n", str, str)

	//5)字符串 转 []byte:  var bytes = []byte("hello go")
	var bytes = []byte("hello go")
	fmt.Printf("bytes=%v\n", bytes)

	//6)[]byte 转 字符串: str = string([]byte{97, 98, 99})
	str = string([]byte{97, 98, 99}) 
	fmt.Printf("str=%v\n", str)

	//10进制转 2, 8, 16进制:  str = strconv.FormatInt(123, 2),返回对应的字符串
	str = strconv.FormatInt(123, 2)
	fmt.Printf("123对应的二进制是=%v\n", str)
	str = strconv.FormatInt(123, 16)
	fmt.Printf("123对应的16进制是=%v\n", str)

	//查找子串是否在指定的字符串中: strings.Contains("seafood", "foo") //true
	b := strings.Contains("seafood", "mary")
	fmt.Printf("b=%v\n", b) 

	//统计一个字符串有几个指定的子串 ： strings.Count("ceheese", "e") //4
	num := strings.Count("ceheese", "e")
	fmt.Printf("num=%v\n", num)

	//10)不区分大小写的字符串比较(==是区分字母大小写的): fmt.Println(strings.EqualFold("abc", "Abc")) // true

	b = strings.EqualFold("abc", "Abc")
	fmt.Printf("b=%v\n", b) //true

	fmt.Println("结果","abc" == "Abc") // false //区分字母大小写

	//11)返回子串在字符串第一次出现的index值，如果没有返回-1 : 
	//strings.Index("NLT_abc", "abc") // 4

	index := strings.Index("NLT_abcabcabc", "abc") // 4
	fmt.Printf("index=%v\n",index)

	//12)返回子串在字符串最后一次出现的index，
	//如没有返回-1 : strings.LastIndex("go golang", "go")

	index = strings.LastIndex("go golang", "go") //3
	fmt.Printf("index=%v\n",index)

	//将指定的子串替换成 另外一个子串: strings.Replace("go go hello", "go", "go语言", n) 
	//n可以指定你希望替换几个，如果n=-1表示全部替换

	str2 = "go go hello"
	str = strings.Replace(str2, "go", "北京", -1)
	fmt.Printf("str=%v str2=%v\n", str, str2)

	//按照指定的某个字符，为分割标识，将一个字符串拆分成字符串数组： 
	//strings.Split("hello,wrold,ok", ",")
	strArr := strings.Split("hello,wrold,ok", ",")
	for i := 0; i < len(strArr); i++ {
		fmt.Printf("str[%v]=%v\n", i, strArr[i])
	} 
	fmt.Printf("strArr=%v\n", strArr)

	//15)将字符串的字母进行大小写的转换: 
	//strings.ToLower("Go") // go strings.ToUpper("Go") // GO

	str = "goLang Hello"
	str = strings.ToLower(str) 
	str = strings.ToUpper(str) 
	fmt.Printf("str=%v\n", str) //golang hello

	//将字符串左右两边的空格去掉： strings.TrimSpace(" tn a lone gopher ntrn   ")
	str = strings.TrimSpace(" tn a lone gopher ntrn   ")
	fmt.Printf("str=%q\n", str)

	//17)将字符串左右两边指定的字符去掉 ： 
	//strings.Trim("! hello! ", " !")  // ["hello"] //将左右两边 ! 和 " "去掉
	str = strings.Trim("! he!llo! ", " !")
	fmt.Printf("str=%q\n", str)

	//20)判断字符串是否以指定的字符串开头: 
	//strings.HasPrefix("ftp://192.168.10.1", "ftp") // true

	b = strings.HasPrefix("ftp://192.168.10.1", "hsp") //true
	fmt.Printf("b=%v\n", b)
}