#include <stdio.h>
#include <stdlib.h>
#define Max 100
/* This program can help you calculate huge numbers (∈ ℕ) */
// Using the function 'strlen()' is not that efficient

int max(char *array_I, int array_I_size, char *array_II, int array_II_size){ 
	// array_I ≥ array_II → 1
        // array_I < array_II → 2
	if(array_I_size > array_II_size) return 1;
	else if(array_II_size > array_I_size) return 2;
	else{
		int i = 0;
		while(1){
			if(i == array_I_size) return 1;
			if(array_I[i] > array_II[i]) return 1;
			else if(array_I[i] < array_II[i]) return 2;
			i ++;
		}
	}
}

int array_addition(char *array, char *array_I, int array_I_size, char *array_II, int array_II_size){
	/* array can be same with array_I */
	int i, j;
	char converted_array[Max] = {0, };
	i = 0;
	if(array_I_size > array_II_size){
		while(1){
			if(i < array_I_size){
				converted_array[i] += array_I[array_I_size - 1 - i];
				if(i < array_II_size) converted_array[i] += array_II[array_II_size - 1 - i];
				converted_array[i + 1] += converted_array[i] / 10;
				converted_array[i] %= 10;
			}
			else break;
			i ++;
		}
	}
	else{
		while(1){
			if(i < array_II_size){
				converted_array[i] += array_II[array_II_size - 1 - i];
				if(i < array_I_size) converted_array[i] += array_I[array_I_size - 1 - i];
				converted_array[i + 1] += converted_array[i] / 10;
				converted_array[i] %= 10;
			}
			else break;
			i ++;
		}
	}
	if(converted_array[i] != 0) i ++;
	for(j = 0; j < i; j ++) array[j] = converted_array[i - 1 - j];
	return i;
}

int converted_array_addition(char *array, char *array_I, int array_I_size, char *array_II, int array_II_size){
	/* this function is used when multiplying */
	int i, j;
	for(i = 0; i < Max; i ++) array[i] = 0;
	i = 0;
	if(array_I_size > array_II_size){
		while(1){
			if(i < array_I_size){
				array[i] += array_I[i];
				if(i < array_II_size) array[i] += array_II[i];
				array[i + 1] += array[i] / 10;
				array[i] %= 10;
			}
			else break;
			i ++;
		}
	}
	else{
		while(1){
			if(i < array_II_size){
				array[i] += array_II[i];
				if(i

 < array_I_size) array[i] += array_I[i];
				array[i + 1] += array[i] / 10;
				array[i] %= 10;
			}
			else break;
			i ++;
		}
	}
	if(array[i] != 0) i ++;
	return i;
}

int array_subtraction(char *array, char *array_I, int array_I_size, char *array_II, int array_II_size){
	/* array can be same with array_I */
	int i, j;
	char converted_array[Max] = {0, };
	for(i = 0; i < Max; i ++) array[i] = 0;
	i = 0;
	while(1){
		if(i < array_I_size){
			converted_array[i] += array_I[array_I_size - 1 - i];
			if(i < array_II_size) converted_array[i] -= array_II[array_II_size - 1 - i];
			if(converted_array[i] < 0){
				converted_array[i] += 10;
				converted_array[i + 1] --;
			}
		}
		else break;
		i ++;
	}
    while(1){ // Ex. 112 - 93 = 019 →19
		if(converted_array[i - 1] != 0) break;
		if(i == 0) return 1; // only if array_I = array_II
		i --;
	}
	for(j = 0; j < i; j ++) array[j] = converted_array[i - 1 - j];
	return i;
}

int array_multiplication(char *array, char *array_I, int array_I_size, char *array_II, int array_II_size){
	/* array can be same with array_I */
	if((array_I_size == 1 && array_I[0] == 0) || (array_II_size == 1 && array_II[0] == 0)){
		array[0] = 0; // if this source doesn't exist, "array = 0" can't be realized(①)
		return 1;
	}
	int i, j, k, temp;
	int size = 0; // 'size' means the size of converted_array at each situation
	char converted_array[Max];
	char notepad_I[Max];
	char notepad_II[Max];
	for(i = 0; i < Max; i ++) converted_array[i] = 0;
	for(i = 0; i < array_II_size; i ++){ // array_II[i] is such 7(i = 0) or 6(i = 1)
		for(j = 0; j < Max; j ++){ // Ex. 132 × 76
			notepad_I[j] = 0; // notepad_I can be 792, 9240
		}
		for(j = 0; j < array_I_size; j ++){ // array_I[j] is such 1(j = 0), 3(j = 1), or 2(j = 2)
			temp = array_I[array_I_size - 1 - j] * array_II[array_II_size - 1 - i];
			notepad_I[j + i] += temp % 10;
			notepad_I[j + i + 1] += temp / 10;
		}
		if(notepad_I[j + i] != 0) j ++;
		for(k = 0; k < size; k ++) notepad_II[k] = converted_array[k];
		/* notepad_II totally

 equals to converted_array */
		size = converted_array_addition(converted_array, notepad_II, size, notepad_I, j + i);
	}
	for(i = 0; i < size - 1; i ++){
		if(converted_array[i] < 0){
			converted_array[i] += 10;
			converted_array[i + 1] --;
		}
	}
	j = size - 1;
	while(1){
		if(converted_array[j] != 0) break; // this is related with ①
		j --;
	}
	for(i = 0; i < j + 1; i ++) array[i] = converted_array[j - i];
	return j + 1;
}

int array_division(char *array, char *array_I, int array_I_size, char *array_II, int array_II_size){
	/* array should not be same with array_I (∵ Information Loss) */
	int i, j, k, l, x;
	char notepad_I[Max];
	char notepad_II[Max];
	char notepad_III[Max];
	char notepad_IV[Max];
	char number[1];
	for(i = 0; i < Max; i ++) array[i] = 0;
	if(array_I_size < array_II_size) return 1;
	i = 0;
	while(1){ // Example: 1237 ÷ 117
		if(i == array_I_size) return 1; // cf. it means array_I < array_II
		for(j = 0; j <= i; j ++) notepad_I[j] = array_I[j]; // notepad_I can be 1, 12, 123, but 1237
		if(max(notepad_I, i + 1, array_II, array_II_size) == 1) break;
		i ++;
	}
	for(j = 0; j < array_I_size; j ++) notepad_II[j] = array_I[j];
	for(j = i; j < array_I_size; j ++){
		k = 0;
		while(1){
			if(notepad_II[k] != 0) break; // notepad_II will be 1237, 0067
			k ++;
		}
		for(l = k; l <= j; l ++) notepad_I[l - k] = notepad_II[l]; // notepad_I will be 123, 67
		for(l = 0; l <= 10; l ++){
			number[0] = l;
			x = array_multiplication(notepad_III, number, 1, array_II, array_II_size);
			if(max(notepad_I, j - k + 1, notepad_III, x) == 2) break;
			/* cf. notepad_III can be (array_II ×0) ~ (array_II ×9) */
		}
		if(l == 0) array[j - i] = 0;
		else array[j - i] = l - 1; // array_II ×(l - 1) ≤ notepad_I < array_II ×l
		number[0] = l - 1;
		x = array_multiplication(notepad_III, number, 1, array_II, array_II_size); // notepad_III = array_II ×(k - 1)
		x = array_subtraction(notepad_IV, notepad_I, j - k + 1, notepad_III, x);
		for(l = 0; l

 < j - x + 1; l ++) notepad_II[l] = 0;
		for(l = j - x + 1; l <= j; l ++) notepad_II[l] = notepad_IV[l - (j - x + 1)];
	}
	return j - i;
}

int array_remainder(char *array, char *array_I, int array_I_size, char *array_II, int array_II_size){
	int i, j, k, l, x;
	char notepad_I[Max];
	char notepad_II[Max];
	char notepad_III[Max];
	char notepad_IV[Max];
	char number[1];
	for(i = 0; i < Max; i ++) array[i] = 0;
	if(array_I_size < array_II_size){
		for(i = 0; i < array_I_size; i ++)
			array[i] = array_I[i];
		return array_I_size;
	}
	i = 0;
	while(1){
		if(i == array_I_size){
			for(i = 0; i < array_I_size; i ++)
				array[i] = array_I[i];
			return 1;
		}
		for(j = 0; j <= i; j ++) notepad_I[j] = array_I[j];
		if(max(notepad_I, i + 1, array_II, array_II_size) == 1) break;
		i ++;
	}
	for(j = 0; j < array_I_size; j ++) notepad_II[j] = array_I[j];
	for(j = i; j < array_I_size; j ++){
		k = 0;
		while(1){
			if(notepad_II[k] != 0) break;
			k ++;
		}
		for(l = k; l <= j; l ++) notepad_I[l - k] = notepad_II[l];
		for(l = 0; l <= 10; l ++){
			number[0] = l;
			x = array_multiplication(notepad_III, number, 1, array_II, array_II_size);
			if(max(notepad_I, j - k + 1, notepad_III, x) == 2) break;
		}
		number[0] = l - 1;
		x = array_multiplication(notepad_III, number, 1, array_II, array_II_size);
		x = array_subtraction(notepad_IV, notepad_I, j - k + 1, notepad_III, x);
		for(l = 0; l < j - x + 1; l ++) notepad_II[l] = 0;
		for(l = j - x + 1; l <= j; l ++) notepad_II[l] = notepad_IV[l - (j - x + 1)];
	}
	k = 0;
	while(1){
		if(notepad_II[k] != 0) break;
		if(k == array_I_size){
			array[0] = 0;
			return 1;
		}
		k ++;
	}
	for(l = k; l < array_I_size; l ++) array[l - k] = notepad_II[l];
	return array_I_size - k;
}

int main(int argc, char *argv[]) {
	char array[Max];
	char array_I[Max];
	int array_I_size;
	char array_II[Max];
	int array_II_size;
	char ch; int i, j;
	printf("Enter two natural numbers, a and b.\n");
	i = 0;
	while(1){
		ch

 = getchar();
		if(ch < 33) break; // ch = 32 ↔ ch = ' '
		array_I[i] = ch - '0';
		i ++;
	}
	array_I_size = i;
	i = 0;
	while(1){
		ch = getchar();
		if(ch < 33) break;
		array_II[i] = ch - '0';
		i ++;
        }
	array_II_size = i;

	printf("a + b = ");
	i = array_addition(array, array_I, array_I_size, array_II, array_II_size);
	for(j = 0; j < i; j ++) printf("%d", array[j]);
	printf("\n");
	printf("a - b = ");
	if(max(array_I, array_I_size, array_II, array_II_size) == 1){
		i = array_subtraction(array, array_I, array_I_size, array_II, array_II_size);
		for(j = 0; j < i; j ++) printf("%d", array[j]);
	}
	else{
		printf("-");
		i = array_subtraction(array, array_II, array_II_size, array_I, array_I_size);
		for(j = 0; j < i; j ++) printf("%d", array[j]);
	}
	printf("\n");
	printf("a * b = ");
	i = array_multiplication(array, array_I, array_I_size, array_II, array_II_size);
	for(j = 0; j < i; j ++) printf("%d", array[j]);
	printf("\n");
	printf("a / b = ");
	i = array_division(array, array_I, array_I_size, array_II, array_II_size);
	for(j = 0; j < i; j ++) printf("%d", array[j]);
	printf("\n");
	printf("a %% b = ");
	i = array_remainder(array, array_I, array_I_size, array_II, array_II_size);
	for(j = 0; j < i; j ++) printf("%d", array[j]);
	return 0;
}