设计一个字符串处理函数，用指针实现常用字符串操作，包括字符串复制，字符串拼接，字符串比较，求字符串长度

以下是一个使用指针实现常用字符串操作的C++函数示例：

#include <iostream>
#include <cstring>
using namespace std;

// 字符串复制
char* mystrcpy(char* dest, const char* src) {
    char* p = dest;
    while (*src != '\0') {
        *p++ = *src++;
    }
    *p = '\0';
    return dest;
}

// 字符串拼接
char* mystrcat(char* dest, const char* src) {
    char* p = dest + strlen(dest);
    while (*src != '\0') {
        *p++ = *src++;
    }
    *p = '\0';
    return dest;
}

// 字符串比较
int mystrcmp(const char* str1, const char* str2) {
    while (*str1 != '\0' && *str2 != '\0') {
        if (*str1 != *str2) {
            return *str1 - *str2;
        }
        str1++;
        str2++;
    }
    return *str1 - *str2;
}

// 求字符串长度
int mystrlen(const char* str) {
    int len = 0;
    while (*str++ != '\0') {
        len++;
    }
    return len;
}

int main() {
    char str1[30] = "Hello";
    char str2[] = "World";
    char str3[30] = "Hello";
    char str4[] = "World";
    char str5[30] = "Hello";
    char str6[] = "World";
    char str7[30] = "Hello";
    char str8[] = "World";
    char str9[30] = "Hello";
    char str10[] = "World";
    char str11[30] = "Hello";
    char str12[] = "World";
    char str13[30] = "Hello";
    char str14[] = "World";
    char str15[30] = "Hello";
    char str16[] = "World";
    char str17[30] = "Hello";
    char str18[] = "World";
    char str19[30] = "Hello";
    char str20[] = "World";

    cout << "复制前：" << str1 << endl;
    mystrcpy(str1, str2);
    cout << "复制后：" << str1 << endl;

    cout << "拼接前：" << str3 << endl;
    mystrcat(str3, str4);
    cout << "拼接后：" << str3 << endl;

    cout << "比较结果：" << mystrcmp(str5, str6) << endl;

    cout << "字符串长度：" << mystrlen(str7) << endl;

    return 0;
}