实现字符串函数，strlen(),strcpy(),strcmp(),strcat()

实现字符串函数，strlen(),strcpy(),strcmp(),strcat()

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

 int my_strlen(char *str);
 char *my_strcpy(char *dest, char *src);
 char *my_strcat(char *dest, char *src);
 int my_strcmp(char *str1,char *str2);

 int main()
 {
     char dest[] = "chen";
     char src[] = "chengha";
     int res;
     //printf("strlen(%s) = %d\n",str,my_strlen(str));
     res = my_strcmp(dest,src);
     printf("res = %d\n",res);
     //puts(dest);
     system("pause");
     return ;
 }

 int my_strlen(char *str)
 {
     int len = ;
     while(*str != '\0')
     {
         len++;
         str++;
     }
     return len;
 }

 char *my_strcpy(char *dest, char *src)
 {
     char *address = dest;
     while((*dest = *src) != '\0')
     {
         dest++;
         src++;
     }
     return address;
 }

 char *my_strcat(char *dest, char *src)
 {
     char *address = dest;
     while(*dest != '\0')
         dest++;
     while((*dest = *src) != '\0')
     {
         dest++;
         src++;
     }
     return address;
 }

 int my_strcmp(char *str1,char *str2)
 {
     for(; *str1 == *str2; str1++, str2++)
         if(*str1 == '\0')
             return ;
     return *str1 - *str2;
 }