#include <iostream>  using namespace std;  //实现一个函数求字符串的长度。  int my_length(const char *s)  {      if (*s == '\0')return 0;      else          return 1+my_length(s + 1);  }  int main()  {      char *s = "123456";      cout << my_length(s) << endl;      return 0;  }    #include <iostream>  #include <assert.h>  using namespace std;  //实现一个求字符串的长度。  int my_length(const char *s)  {      if (s == NULL)return 0;      int count = 0;      while (s[++count] != '\0');      return count;  }  int main()  {      char *s = "";      cout << my_length(s) << endl;      return 0;  }      #include <iostream>  #include <string.h>  #include <assert.h>  using namespace std;    char* my_strcpy(char *dist,const char *scour)  {      assert(scour!=NULL);      char *p = dist;      while (*dist++ = *scour++);      return p;  }  int main()  {      char *s1 = "123";      char *s2 = new char[strlen(s1)];      cout << my_strcpy(s2, s1) << endl;      return 0;  }    #include <iostream>  #include <assert.h>  using namespace std;  //实现库函数strcat。  char * my_strcat(char *dist,char const *scour)  {      assert(dist!=NULL || scour!=NULL);      if (*scour == '\0')return dist;      char *p = dist;      while (*dist != '\0')dist++;      while (*dist++ = *scour++);      return p;  }  int main()  {      char *s1 = new char[10];      strcpy(s1,"123");      cout << my_strcat(s1,"456")<<endl;      return 0;  }    #include <iostream>  #include <assert.h>  #include <string.h>  using namespace std;  //编写程序使字符串逆序。  char* my_invert(char *s)  {      assert(s != NULL);      char *head = s;      char *last = s+strlen(s)-1;      char temp;      while (head < last)      {          temp = *head;          *head = *last;          *last = temp;          head++;          last--;      }      return s;  }  int main()  {      char *s = new char[10];      strcpy(s,"12345");      cout << my_invert(s) << endl;      return 0;  }  #include <iostream>  #include <assert.h>  using namespace std;  //模拟实现strchr函数，功能：在一个字符串中查找一个字符第一次出现的位置，如果没有出现返回NULL。  int my_strchar(const char* dist, char ch)  {      assert(dist!=NULL);      int count = 0;      while (*dist != '\0' && *dist!=ch)      {          count++;          dist++;      }      if (*dist == '\0')return 0;      return count+1;  }  int main()  {      cout << my_strchar("1234", '1') << endl;      return 0;  }