strcpy strcat strlen实现

char * strcpy (char *strDes, const char *strSrc) 
{
　assert((strDes != NULL) && (strSrc != NULL) );
　char *address = strDes; 
　while((*strDes++ = *strSrc++) != ‘\0‘); //复制-包括‘\0‘
　return address;
}

int strlen(const char* str)
{
  assert(str != NULL);
  int len = 0;
  while((*str++) != ‘\0‘)
  {
      len++;
  }
  return len;              
}