#include<iostream>using namespace std; // 字符串长度函数int strLength(char *s){    int i=0;    while(s[i] != '\0'){        i++;    }    return i;}  // 字符串连接函数int strCincat(char *s1, char *s2, char *s){    int i=0;    int j=0;    while(s1[i] != '\0'){        s[i] = s1[i];        i++;    }    while(s2[j] != '\0'){        s[i] = s2[j];        i++;        j++;    }    s[i] = '\0'; // 串结束标志    return 1; }  // 子串函数int strsub(char *t, char *s, int i, int len){    int slen;    slen = strLength(s);    if(i<1 || i>slen || len<0 || len>slen-i+1){        return 0;    }    int j=0;    for(j;j<len;j++){        t[j] = s[i-j+1];        }    t[j] = '\0';    return 1;}  // 字符串比较函数int strComp(char *s1, char *s2){    int i=0;    while(s1[i] == s2[i] && s1[i] != '\0' && s2[i] != '\0'){        i++;    }    return (s1[i] - s2[i]);}  // 字符串匹配函数int strFind(char *s, char *t){    int i=0;    int j=0;    while(s[i] != '\0' && t[j] != '\0'){        if(s[i] == t[j]){            i++;            j++;        }else{            i = i-j+1;            j = 0;        }     }    if(t[j] == '\0') return i-j; // 匹配成功，返回下标     else return 0; } int main() {    // 测试strLength    char str1[] = "Hello";    cout << "Length of '" << str1 << "' is: " << strLength(str1) << endl;     // 测试strCincat    char str2[] = "World";    char result[50];    strCincat(str1, str2, result);    cout << "Concatenation of '" << str1 << "' and '" << str2 << "' is: " << result << endl;     // 测试strsub    char subStr[50];    if(strsub(subStr, str1, 2, 3)) {        cout << "Substring from position 2 with length 3: " << subStr << endl;    } else {        cout << "Invalid substring parameters." << endl;    }     // 测试strComp    char str3[] = "Hello";    char str4[] = "Hello";    cout << "Comparison of '" << str3 << "' and '" << str4 << "': " << strComp(str3, str4) << endl;     char str5[] = "Hello";    char str6[] = "World";    cout << "Comparison of '" << str5 << "' and '" << str6 << "': " << strComp(str5, str6) << endl;     // 测试strFind    char str7[] = "Hello World";    char str8[] = "World";    int index = strFind(str7, str8);    if(index) {        cout << "Found substring '" << str8 << "' in '" << str7 << "' at position: " << index << endl;    } else {        cout << "Substring not found." << endl;    }     return 0;}