//方式一：定义一个计数器
size_t my_strlen(const char *str)
{
  int count = 0;   
  while (*str)
  {
    count++;     
    str++;
  }
  return count;
}

size_t my_strlen(const char *str)
{
  if (*str == '\0')
    return 0;
  else
    return my_strlen(str + 1) + 1;
}

size_t my_strlen(const char *str)
{
  const char *end = str;
  while (*end++)
  {
    ;
  }
  return end - str - 1;
}

char *strcpy(char *dest, const char *src);

char *my_strcpy(char *dest, const char *src)
{
  char *tmp = dest;
  assert(dest);
  assert(src);
  while (*dest++ = *src++)
  {
    ;
  }
  return tmp;
}

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

int my_strcmp(const char *src1, const char *src2)
{
  while (*src1 == *src2)
  {
    if (*src1 == '\0')
      return 0;
    src1++;
    src2++;
  }
  return *src1 - *src2;
}

char *my_strstr(const char* s1, const char* s2)
{
  const char *p = s1;
  const char *q = s2;
  const char *cur = NULL;
  assert(s1);
  assert(s2);
  if (*s2 == '\0')
    return s1;
  while (*p)
  {
    cur = p;
    while ((*p) && (*q) && (*p == *q))
    {
      p++;
      q++;
    }
    if (*q == '\0')
      return cur;
    p = cur + 1;
    q = s2;
  }
  return NULL;
}

char *my_strchr(char const *str, int ch)
{
  const char *tmp = str;
  while (*tmp)
  {
    if (*tmp == ch)
    {
      return tmp;
    }
    tmp++;
  }
  return NULL;
}

char* my_strrchr(const char* str, int ch)
{
  char* pos = 0;
  assert(str);
  while (*str)
  {
    if (*str == ch)
    {
      pos = str;
    }
    str++;
  }
  if (pos != 0)
  {
    return pos;
  }
  else
    return NULL;
}

char *my_strncpy(char *dest, const char *src, size_t len)
{
  char *ret = dest;
  size_t i = 0;
  assert(dest);
  assert(src);
  while (len--)
  {
    *ret++ = *src++;
  }
  if (*(ret) != '\0')
  {
    *ret = '\0';
  }
  return dest;
}

char *my_strncat(char *dst, const char *src, size_t len)
{
  char *ret = dst;
  assert(dst);
  assert(src);
  while (*dst != '\0')
  {
    dst++;
  }
  while (len--)
  {
    *dst = *src;
    dst++;
    src++;
  }
  return ret;
}

int my_strncmp(char const *s1, char const *s2, size_t len)
{
  assert(s1);
  assert(s2);
  while (len--)
  {
      if (*s1 == *s2)
      {
        s1++;
        s2++;
      }
      else
      {
        return *s1 - *s2;
      }
  }
    return 0;
}