#include <stdio.h>

#define SIZE 4

main()
{
	/* Digits of numbers are stored in reverse order */
	char number1[SIZE]; /* First number */
	char number2[SIZE]; /* Second number */
	char number3[SIZE]; /* Stores the sum */

	char symbol; /* Stores current input symbol */
	char temp[SIZE]; /* temporary storage for numbers */
	int size; /* stores the number of digits is input */

	/* Read the first number and store it in number1 */

	printf("Input a number of at most %d digits: ", SIZE);
	symbol = getchar(); /* read first symbol */
	for (size = 0; 1; size++) {
		if ((symbol < '0') || (symbol > '9')) /* not a digit */
			break;
		if (size == SIZE) { /* input too large */
			printf("Input too large: number should be at most %d digits\n", SIZE);
			return;
		}
		temp[size] = symbol - '0';
		symbol = getchar(); /* read next symbol */
	}

	/* Store number in reverse order */
	int i;

	for (i = 0; i < size; i++)
		number1[i] = temp[size-1-i];
	for (i = size; i < SIZE; i++)
		number1[i] = 0;

	/* First number read.
	 * Now read the second numnber.
	 */

	printf("Input a number of at most %d digits: ", SIZE);
	symbol = getchar(); /* read first symbol */

	for (size = 0; 1; size++) {
		if ((symbol < '0') || (symbol > '9')) /* not a digit */
			break;
		if (size == SIZE) { /* input too large */
			printf("Input too large: number should be at most %d digits\n", SIZE);
			return;
		}
		temp[size] = symbol - '0';
		symbol = getchar(); /* read next symbol */
	}

	/* Store number in reverse order */

	for (i = 0; i < size; i++)
		number2[i] = temp[size-1-i];
	for (i = size; i < SIZE; i++)
		number2[i] = 0;

	/* Second number read.
	 * Now add the two.
	 */

	int carry; /* Stores the carry value */

	for (i = 0, carry = 0; i < SIZE; i++) {
		number3[i] = number1[i] + number2[i] + carry;
		if (number3[i] > 9) { /* new carry created */
			number3[i] = number3[i] - 10;
			carry = 1;
		}
		else /* no carry created */
			carry = 0;
	}

	if (carry == 1) { /* sum too large */
		printf("The sum is too large!\n");
		return;
	}

	/* Addition complete.
	 * Now output the sum.
	 */

	/* Skip the leading zeroes */
	for (i = SIZE-1; i >= 0; i--)
		if (number3[i] > 0)
			break;
	
	if (i == 0) /* the sum is zero! */
		printf("The sum is: 0\n");
	else {
		printf("The sum is: ");
		for (; i >= 0; i--)
			putchar(number3[i]+'0');
		printf("\n");
	}
	
	/* All done! */
}