如何更改字符串首字母的大小写？

def change_case(s):
    return s[0].upper() + s[1:].lower()

s = "hello world"
result = change_case(s)
print(result)  # 输出 "Hello world"

function changeCase(s) {
    return s[0].toUpperCase() + s.slice(1).toLowerCase();
}

let s = "hello world";
let result = changeCase(s);
console.log(result);  // 输出 "Hello world"

public class Main {
    public static String changeCase(String s) {
        return s.substring(0, 1).toUpperCase() + s.substring(1).toLowerCase();
    }

    public static void main(String[] args) {
        String s = "hello world";
        String result = changeCase(s);
        System.out.println(result);  // 输出 "Hello world"
    }
}

using System;

class Program {
    static string ChangeCase(string s) {
        return char.ToUpper(s[0]) + s.Substring(1).ToLower();
    }

    static void Main() {
        string s = "hello world";
        string result = ChangeCase(s);
        Console.WriteLine(result);  // 输出 "Hello world"
    }
}

function changeCase($s) {
    return ucfirst(strtolower($s));
}

$s = "hello world";
$result = changeCase($s);
echo $result;  // 输出 "Hello world"

def change_case(s)
    s[0].upcase + s[1..-1].downcase
end

s = "hello world"
result = change_case(s)
puts result  # 输出 "Hello world"

package main

import (
	"fmt"
	"strings"
)

func changeCase(s string) string {
	return strings.ToUpper(string(s[0])) + strings.ToLower(s[1:])
}

func main() {
	s := "hello world"
	result := changeCase(s)
	fmt.Println(result)  // 输出 "Hello world"
}