#include <stdio.h>
#define SIZE 10

char skip_blanks();
int read_number();
void multiply_numbers();
void output_number();

/*  Reads two positive numbers of at most SIZE many digits
 *  and outputs their product.
 */
main()
{
        char number1[SIZE]; //Store first number
        char number2[SIZE]; //store second number
	char product[SIZE*2]; // Stores the result of multiplication

	/* Read first number */
	if (read_number(number1) == 0) // Wrong input
		return;

	/* Read second number */
	if (read_number(number2) == 0) // Wrong input
		return;

	/* Multiply numbers */
	multiply_numbers(number1, number2, product);

	/* Output the result */
	output_number(product);
}


/* Reads a positive number of at most SIZE digits */
int read_number(char number[])
{
	char temp[SIZE];
	int i;
	int size; // Records the number of digits in the read number
	char symbol; // Stores the current symbol read

	/*Initialising array number to zero */
	for(i=0; i < SIZE; i++)
		number[i] = 0;  

	// read number
        printf("Please enter the first number of atmost %d digits: ",SIZE);

	symbol = skip_blanks();
	for(size = 0; 1; size++) { /* reading number digit-by-digit */
		if ((symbol < '0')|| (symbol > '9'))
			break;  /*breaking the loop on entering non digit*/ 	
					                                                  
		if(size == SIZE) {
			printf("The number is too large\n");/* If the number is too long then exit*/
			return 0; // Return error
		}
		temp[size] = symbol - '0'; /*storing number in temporary location*/
		symbol = getchar(); /*reading input digit by digit*/	
	}

	// reversing the digits
	for(i = 0; i < size; i++) {
		number[i] = temp[size-i-1];
	}

	return 1; // return success
}

/* Multiplies two given numbers and stores the result in product array */
void multiply_numbers(char number1[], char number2[], char product[])
{
	int carry; // Stores the carry
	char temp[2*SIZE]; // Stores the multiplication of one digit of number1 with number2
	int i;
	int j;
	int k;

	/* Initialize the arrays temp and product */
	for (i = 0; i < 2*SIZE; i++) {
		temp[i] = 0;
		product[i] = 0;
	}

	/* Multiply two numbers by multiplying each digit of number1 to number2 and summing the results */
	for(i = 0; i < SIZE; i++) { /*selecting the digit from first number*/

		/* First, multiply the digit of number1 with number2 */
		carry = 0; // carry is zero in the beginning of multiplication
		for(j = 0; j < SIZE; j++) { /* multiplying the selected digit with second num */
			k = number2[j] * number1[i] + carry;
			temp[i+j] = k % 10;
			carry = k / 10;
		}

		/* Now add this to the sum of previous multiplications */
		carry = 0; // carry is zero in the beginning of addition
		/* performing addition of the product of digits of second number with the first number*/ 
		for(j = 0; j < 2*(SIZE); j++) {
			k = temp[j] + product[j] + carry;
			product[j] = k % 10;
			carry = k / 10;
		}

		for(j = 0; j < 2*SIZE; j++) // reset temp to zero
			temp[j] = 0;
	}
}

/* Outputs the number */
void output_number(char number[])
{
	int i;

	for (i = 2*SIZE-1; i >= 0; i--)
		if (number[i] > 0)// ignoring all zeros
			break;
	
	if (i == -1) /* the sum is zero! */
		printf("The product is: 0\n");
	else {
		printf("The product is: ");
		for (; i >= 0; i--)
			putchar(number[i]+'0');
		printf("\n");
	}
}


/* Skips white spaces and returns the first non-white space symbol */
char skip_blanks()
{
	char c;

	c = getchar(); // read a symbol

	// Skip symbols until a non-white space is found
	for (; (c == ' ') || (c == '\n') || (c == '\t'); )
		c = getchar();
	
	return c;
}