isalpha ( )【C语言库函数源代码】

【C语言库函数源代码】

【本程序在Dev C++ 4.9.9.2 下编译通过】

int my_isalpha(int ch )

{

   return (unsigned int)((ch | 0x20) - 'a') < 26u;

}//判断字符c是否为英文字母

int main()

{

   char ch = 'c';

   if(my_isalpha(ch))

      printf("%c is English Character!\n",ch);

   else

      printf("%c is not a English Character!\n",ch);

   ch = 'A';

   if(my_isalpha(ch))

      printf("%c is English Character!\n",ch);

   else

      printf("%c is not a English Character!\n",ch);

   ch = '1';

   if(my_isalpha(ch))

      printf("%c is English Character!\n",ch);

   else

      printf("%c is not a English Character!\n",ch);

 

   system("pause");

   return 0;

}