/* A program to add two 4-bit unsigned binary numbers
 * NOTE: Result is a 5-bit number 
 *
 * Programmed by: Fran Jarnjak
 * 1/29/2003 
 */


#include <iostream.h>

// Function that adds parameter 'first' and parameter 'second' 
// while taking into the account possible carry. 

// All the parameters are in binary - either 1 or 0
// Parameter that holds carry should be passed by address (reference) 

// Return value of the function is either 1 or 0 which is the result of the addition and
// carry parameter is updated as well to hold correct value. 

int binaryAdd(int first, int second, int * carry) {

	int result;

	// exhaust all of the possible cases as described in the handout

	if(first==0 && second==0) {
		result = (*carry);
		*carry = 0;
	}

	else if(first==0 && second==1) { 		
		if(*carry==0) 
			result = 1;
		else {
			result = 0;
			*carry = 1;
		}
	}

	else if(first==1 && second==0) { 
		if(*carry==0) {
			result = 1;			
		} else {
			result = 0;
			*carry = 1;
		}
	} else if(first==1 && second==1) { 
	
		if(*carry==0) {
			result = 0;
			*carry = 1;
		} else {
			result = 1;
			*carry = 1;
		}
	}

	return result;
}


int main(void) { 

	int i;          // loop counter
	int carry=0;		// Initialize carry to 0 (IMPORTANT)

					// MSB - Most significant bit  (leftmost)
					// LSB - Least significant bit (rightmost)
	int num1[4];	// MSB - index 0 LSB index 3
	int num2[4];	// MSB - index 0 LSB index 3
	int result[5];	// MSB - index 0 LSB index 4

	char e_result[6]; // 5+null char
	char e_num1[5]; // 4+null char
	char e_num2[5]; // 4+null char

	// get data

	cout << "Enter first number: ";
	cin >> e_num1; 
	cout << "Enter second number: ";
	cin >> e_num2;

	// convert from char array to int array
	// It is useful to have data in int array when doing conversion into decimal 
	// value of a certain binary number which is not implemented in this program. 

	for(i=0;i<4;i++) {
		
		// NOTE: No checking that the actual number entered is indeed
		//		 a binary number
		//
		//		 ASCII value of '0' = 48
		//		 ASCII value of '1' = 49
		
		num1[i] = e_num1[i]-48;  
		num2[i] = e_num2[i]-48;
		
	}

	// initialize result array
	for(i=0;i<5;i++) result[i] = 0;


	// do the addition	
	for(i=3;i>=0;i--) { // go from right to left (LSB to MSB)
		
		result[i+1] = binaryAdd(num1[i],num2[i],&carry); // needs to add 1 to the counter
														 // since LSB index for result 
														 // is 1 more than LSB of operands		

		e_result[i+1] = result[i+1]+48; // For display purposes - convert to char array
	}

	result[0] = carry; // Add MSB of result
	e_result[0] = result[0] + 48; 
	e_result[5] = '\0'; // Put NULL Char

	// print out the results

	cout << "   " << e_num1 << endl;
	cout << "  +" << e_num2 << endl;
	cout << "  -----" << endl;
	cout << "  " << e_result << endl << endl;

	return 0; // since main() has a return type int; for UNIX compiler compatibility

}