C语言输入验证

// checking.c -- validating input
#include <stdio.h>
#include <stdbool.h>
// validate that input is an integer
long get_long(void);
// validate that range limits are valid
bool bad_limits(long begin, long end,
                long low, long high);
// calculate the sum of the squares of the integers
// a through b
double sum_squares(long a, long b);
int main(void)
{
    const long MIN = -10000000L;  // lower limit to range
    const long MAX = +10000000L;  // upper limit to range
    long start;                   // start of range
    long stop;                    // end of range
    double answer;

    printf("This program computes the sum of the squares of "
           "integers in a range.\nThe lower bound should not "
           "be less than -10000000 and\nthe upper bound "
           "should not be more than +10000000.\nEnter the "
           "limits (enter 0 for both limits to quit):\n"
           "lower limit: ");
    start = get_long();
    printf("upper limit: ");
    stop = get_long();
    while (start !=0 || stop != 0)
    {
        if (bad_limits(start, stop, MIN, MAX))
            printf("Please try again.\n");
        else
        {
            answer = sum_squares(start, stop);
            printf("The sum of the squares of the integers ");
            printf("from %ld to %ld is %g\n",
                    start, stop, answer);
        }
        printf("Enter the limits (enter 0 for both "
               "limits to quit):\n");
        printf("lower limit: ");
        start = get_long();
        printf("upper limit: ");
        stop = get_long();
    }
    printf("Done.\n");

    return 0;
}

long get_long(void)
{
    long input;
    char ch;

    while (scanf("%ld", &input) != 1)
    {
        while ((ch = getchar()) != '\n')
            putchar(ch);  // dispose of bad input
        printf(" is not an integer.\nPlease enter an ");
        printf("integer value, such as 25, -178, or 3: ");
    }

    return input;
}

double sum_squares(long a, long b)
{
    double total = 0;
    long i;

    for (i = a; i <= b; i++)
        total += (double)i * (double)i;

    return total;
}

bool bad_limits(long begin, long end,
                long low, long high)
{
    bool not_good = false;

    if (begin > end)
    {
        printf("%ld isn't smaller than %ld.\n", begin, end);
        not_good = true;
    }
    if (begin < low || end < low)
    {
        printf("Values must be %ld or greater.\n", low);
        not_good = true;
    }
    if (begin > high || end > high)
    {
        printf("Values must be %ld or less.\n", high);
        not_good = true;
    }

    return not_good;
}