/*
 * Program to get integer, with check for overflow.
 */
#include <stdio.h>
#include <stdbool.h>
#include <ctype.h>
#include <limits.h>

bool get_int(int * n);

int main(void) {
	printf("enter integer:\n");
	int input;
	if (get_int(&input)) {
		printf("you entered %d\n", input);
	} else {
		printf("error\n");
	}
}
/*
 * function to read int from standard input
 * skips leading whitespace
 * returns true if value up to next whitespace can be converted to "int", 
 *   false otherwise
 */
bool get_int(int * n) {
	int inchar;
	/* skip leading whitespace */
	do {
		inchar = getchar();
	} while (isspace(inchar));

	/* at this point, inchar is first non-whitespace */
	/* look for "-" at start */
	int sign = 1;
	if (inchar == '-') {
		sign = -1;
		inchar = getchar();
	}

	/* at this point, inchar should be start of number */
	if (!isdigit(inchar)) {
		return false;
	}

	/* read in digits up to non-digit and accumulate result */
	/* (have first digit) */
	int temp = 0;
	do {
		int digit = inchar - '0';
		/* want to check temp * 10 + digit > INT_MAX */
		/* but evaluating that could overflow */
		/* test something algebraically equivalent that won't overflow */
		if (temp > (INT_MAX - digit) / 10) {
			return false;
		}
		temp = temp * 10 + digit;
		inchar = getchar();
	} while (isdigit(inchar));

	/* at this point, inchar is the first non-digit */
	/* check for ending whitespace */
	if (!isspace(inchar)) {
		return false;
	} 

	/* store result for caller */
	*n = sign * temp;
	return true;
}