#include "stdio.h"
#include "ctype.h"
char myupper(char ch)
{if(islower(ch))  ch=ch-32;
    return ch;   
    }
main()
{
    char ch;
    while((ch=getchar())!='@')
            {ch=myupper(ch);
            putchar(ch);}
    }

islower(ch)为什么能等价于ch>='a' &&ch<='z'