isalnum ( )【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_isalnum ( int ch )
{
return (unsigned int)((ch | 0x20) - 'a') < 26u ||
(unsigned int)( ch - '0') < 10u;
}//测试参数ch是否是字母(A-Z,大小写均可)或数字（0-9）
int main()
{
char ch = 'c';

if(my_isalnum(ch))
printf("%c is English Character or Number!/n",ch);
else
printf("%c is not a English Character and Number!/n",ch);

ch = '1';

if(my_isalnum(ch))
printf("%c is English Character or Number!/n",ch);
else
printf("%c is not a English Character and Number!/n",ch);

ch = '!';

if(my_isalnum(ch))
printf("%c is English Character or Number!/n",ch);
else
printf("%c is not a English Character and Number!/n",ch);

system("pause");
return 0;
}