将输入作为字符流读取，直到遇到EOF

#include <stdio.h>  
#include <ctype.h>  
int main(void)  
{  
    int ch;  
    unsigned long uct = 0;  
    unsigned long lct = 0;  
    unsigned long oct = 0;  

    while ((ch = getchar()) != EOF)  {
         if (ch >= 'A' && ch <= 'Z')  
             uct++;  
         else if (ch >= 'a' && ch <= 'z')  
             lct++;  
         else  
            oct++;  
    }
    printf("%lu uppercase characters read/n", uct);  
    printf("%lu lowercase characters read/n", lct);  
    printf("%lu other characters read/n", oct);  

    return 0;  
}