用c语言编写一个程序表示字符串的基本操作，包括求串长、赋值、比较、串连接、求子串、替换和定位算法

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// 求串长
int strLength(char* str) {
    int len = 0;
    while (*str != '\0') {
        len++;
        str++;
    }
    return len;
}

// 赋值
void strAssign(char* dst, char* src) {
    while (*src != '\0') {
        *dst = *src;
        dst++;
        src++;
    }
    *dst = '\0';
}

// 比较
int strCompare(char* str1, char* str2) {
    while (*str1 != '\0' && *str2 != '\0') {
        if (*str1 > *str2) {
            return 1;
        } else if (*str1 < *str2) {
            return -1;
        }
        str1++;
        str2++;
    }
    if (*str1 == '\0' && *str2 == '\0') {
        return 0;
    } else if (*str1 == '\0') {
        return -1;
    } else {
        return 1;
    }
}

// 串连接
void strConcat(char* dst, char* str1, char* str2) {
    while (*str1 != '\0') {
        *dst = *str1;
        dst++;
        str1++;
    }
    while (*str2 != '\0') {
        *dst = *str2;
        dst++;
        str2++;
    }
    *dst = '\0';
}

// 求子串
void substr(char* dst, char* src, int start, int len) {
    int i;
    for (i = 0; i < len; i++) {
        dst[i] = src[start + i];
    }
    dst[len] = '\0';
}

// 替换
void strReplace(char* dst, char* src, char* oldStr, char* newStr) {
    int oldLen = strlen(oldStr);
    int newLen = strlen(newStr);
    while (*src != '\0') {
        if (strstr(src, oldStr) == src) {
            strcpy(dst, newStr);
            dst += newLen;
            src += oldLen;
        } else {
            *dst = *src;
            dst++;
            src++;
        }
    }
    *dst = '\0';
}

// 定位算法
int strIndex(char* str, char* subStr) {
    char* p = str;
    char* q = subStr;
    while (*p != '\0' && *q != '\0') {
        if (*p == *q) {
            p++;
            q++;
        } else {
            p = p - q + 1;
            q = subStr;
        }
    }
    if (*q == '\0') {
        return p - str - strlen(subStr) + 1;
    } else {
        return -1;
    }
}

int main() {
    char str1[100] = "hello";
    char str2[100] = "world";
    char str3[100] = "hello";
    char str4[100] = "world";
    char str5[100] = "hello";
    char str6[100] = "world";
    char str7[100] = "hello, world";
    char str8[100] = "world";
    char str9[100] = "hello, world";
    char str10[100] = "world";
    char str11[100] = "hello, world";
    char str12[100] = "world";
    char str13[100] = "hello, world";
    char str14[100] = "world";
    char str15[100] = "hello, world";
    char str16[100] = "world";
    char str17[100] = "hello, world";
    char str18[100] = "world";
    char str19[100] = "hello, world";
    char str20[100] = "world";
    
    printf("str1 length: %d\n", strLength(str1));
    strAssign(str2, str1);
    printf("str2: %s\n", str2);
    printf("str1 compare str3: %d\n", strCompare(str1, str3));
    strConcat(str4, str1, str2);
    printf("str4: %s\n", str4);
    substr(str5, str1, 1, 3);
    printf("str5: %s\n", str5);
    strReplace(str6, str7, str8, str9);
    printf("str6: %s\n", str6);
    int index = strIndex(str11, str12);
    printf("str12 index in str11: %d\n", index);
    
    return 0;
}