#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <string.h>
#include <malloc.h>
#include <assert.h>
#define MAX_SIZE 500



typedef char* verylong;

verylong input_long(void);
verylong add_verylong(verylong vl1, verylong vl2);
verylong add(verylong ln, verylong sn);
verylong multi(verylong vl1, verylong vl2);
int c2n(char ch);
char n2c(int n);



void main() {
	verylong a, b, c;

	do {
		printf("enter the first long integer: ");
		a = input_long();
	} while (!a);
	do {
		printf("enter the second long integer: ");
		b = input_long();
	} while (!b);

	c = add_verylong(a, b);
	printf("%s + %s = %s\n", a, b, c);
	c = multiply_verylong(a, b);
	printf("%s * %s = %s\n", a, b, c);
	free(c);
	free(a);
	free(b);
	//system("pause");
}




verylong input_long(void) {
	/*
	* This function is used to input a 'verylong' number from the user:
	*/

	// Setting up a place in the RAM for the number:
	verylong res = (verylong)malloc(sizeof(char) * MAX_SIZE);
	assert(res);
	char dig;
	int i = 0;

	// Getting the number from the user:
	gets(res);

	// Iterating through 'res' until we reach NULL:
	for (i = 0; *(res + i) != '\0'; i++) {
		dig = *(res + i);
		if ((dig > '9') || (dig < '0')) {
			printf("wrong input");
			return NULL;
		}
	}

	// Finally, returning the place in the memory the correct number is located in, after resizing it and asserting it:
	res = (verylong)realloc(res, sizeof(char) * (strlen(res) + 1));
	assert(res);
	return res;
}




verylong add_verylong(verylong vl1, verylong vl2) {
	/*
	 * Since the logic 'add' function only handles the option in which vl1.size >= vl2.size, we use this function to invoke 'add_vl' properly:
	 */
	if (strlen(vl1) > strlen(vl2)) add_vl(vl1, vl2);
	else add(vl2, vl1);
}



verylong multiply_verylong(verylong vl1, verylong vl2) {
	/*
	 * Since the logic 'multi' function only handles the option in which vl1.size >= vl2.size, we use this function to invoke 'add_vl' properly:
	 */
	if (strlen(vl1) > strlen(vl2)) add_vl(vl1, vl2);
	else add(vl2, vl1);
}



verylong add(verylong ln, verylong sn) {
	/*
	 * This function calculates the sum between numbers when ln is longer than sn physically.
	 */
	int i, j, longerlen, shorterlen, len1 = strlen(ln), len2 = strlen(sn), pow = 1, carry = 0, sum;

	// Allocating memory space for the result: (the size will be the longer number's size +2 for nullchar and carry)
	verylong res = (verylong)calloc(sizeof(char), (len1 + 2)), res_opt = (verylong)calloc(sizeof(char), (len1 + 1));

	// Adding each number exactly like decimal addition:
	for (i = len1, j = len2; i > 0; i--, j--) {
		if (j > 0) {
			sum = c2n(*(ln + -1 + i)) + c2n(*(sn + j - 1)) + carry;
			*(res + i) = n2c((sum % 10));
			carry = sum / 10;
		}
		else {
			sum = c2n(*(ln + i - 1)) + carry;
			*(res + i) = n2c((sum % 10));
			carry = sum / 10;
		}
	}
	*res = '0' + carry * 1;
	*(res + len1 + 1) = '\0';
	if (*res == '0') {
		strcpy(res_opt, res + 1);
		return res_opt;
	}


	return res;
}




verylong multi(verylong ln, verylong sn) {
	/*
	 * This function calculates the multiplication between numbers when ln is longer than sn physically.
	 */
	int i, pow = 1, temp, j, len2;
	// Allocating memory for the reuslt: (the size will be the size of vl1) (this will be changed in future runs)
	verylong res = (verylong)calloc(sizeof(char), (strlen(ln) + 1));
	assert(res);

	*res = '0';
	*(res + 1) = '\0';
	len2 = strlen(sn);

	for (i = len2; i >= 0; i--) {
		// Calculating the temporary vl2 as a number one place at a time:
		temp = c2n(*(ln + i - 1)) * pow;

		// Multiplying vl1 by vl2 one place at a time:
		for (j = 0; j < temp; j++) {
			res = (add_verylong(res, sn));
		}

		// Going up the places:
		pow = pow * 10;
	}

	// Finally, returning the multiplication result:
	return res;
}




/*
 * Those are optional helping functions that help us calculate and convert from int to char and vice versa:
 */
int c2n(char ch) {
	/*
	 * This function converts a charnum into a real int:
	 * (does not have input checking)
	 */

	return (ch - '0');
}




char n2c(int n) {
	/*
	* This function converts a charnum into a real int:
	* (does not have input checking)
	*/

	return (n + '0');
}