# include <stdio.h>
# define COVERAGE 200

int main (void)
{
    int sq_feet;
    int cans;

    printf ("Enter number of square feet to be painted: \n");
    while ( scanf("%d", &sq_feet) == 1 )
    {
        cans = sq_feet / COVERAGE;
        cans = cans + ((sq_feet % COVERAGE == 0))? 0: 1;                             // 改成cans += ((sq_feet % COVERAGE == 0))? 0: 1;  则输出就不再是0
                                                                                        为什么？
        printf ("You need %d %s of paint.\n", cans, cans == 1? "can": "cans");
        printf ("Enter next value(q to quit): \n");
    }
    return 0;
}

应该这样就可以啦 cans = cans + ((sq_feet % COVERAGE == 0)? 0: 1);