// checking.c -- validating input
#include <stdio.h>
#include <stdbool.h>

// validate that input is an integer
int get_int(void);
// validate that range limits are valid
bool bad_limits(int begin, int end, int low, int high);
// calculate the sum on the squares of the integers a through b
double sum_squares(int a, int b);

int main(void)
{
	// lower limit to range
	const int MIN = -1000;
	// upper limit to range
	const int MAX = +1000;
	// start of range
	int start;
	// end of range
	int stop;
	double answer;
	
	printf("This program computers the sum of the squares of integers "
	       "in a range.\nThe lower bound should not be less than -1000 "
	       "and\nthe upper bound should not be more than +1000.\n"
	       "Enter the limits (enter 0 for both limits to quit):\n"
	       "lower limit: ");
	start = get_int();
	printf("upper limit: ");
	stop = get_int();
	
	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 "
			       "from %d to %d is %g\n", start, stop, answer);
		}
		printf("Enter the limits (enter 0 for both limits to quit):\n"
		       "lower limit: ");
		start = get_int();
		printf("upper limit: ");
		stop = get_int();
	}
	printf("Done\n");
	return 0;
}

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

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

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

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