how to add two strings ?

maybe some one will need it sometime :

description:
func in c++ that will add (arythmetic) two string of postive integers
to change it to c :
use malloc insted of new.

Code:

/***************************************************************************
 *            How to add two postive numbers?
 *
 *  Sun Apr 22 09:25:07 2007
 *  Jabka Atu
 *  
 ****************************************************************************/

/*
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */
 
 
#include <iostream>
using namespace std;

char* add_two_postive_numbers(char *first_value,char *second_value){

	char *result=NULL;
		
	char i = 0;
	char ans = '0';
	char carry = 0;
	char size_of_first  = strlen(first_value);
	char size_of_second = strlen(second_value);
	char biggest_size   = (size_of_first > size_of_second) ? size_of_first : size_of_second;
	char smallest_size  = (size_of_first < size_of_second) ? size_of_first : size_of_second;
	char delta = size_of_first - size_of_second;
	
	if (size_of_first < size_of_second)
	{
		result=add_two_postive_numbers(second_value,first_value);
		return result;
	}	
	
	result=new char[biggest_size + 2]; //one more for '\0' and for extra 1
	result[biggest_size + 1] = '\0';
	result[0]			 = '0';
	
	for (i=0;i<size_of_second;i++)
	{
		ans=first_value[size_of_first - i-1] + second_value[size_of_second-i-1] + carry - '0';
		carry=0;

									
		if (ans>'9')
		{
			carry=1;
			result[biggest_size - i] = ans - 10;
				
		}
		else 
		{
			result[biggest_size - i] = ans;
		}
	}
	
	if(!carry)	//since there is an option that there 
				//will be no borrow i will cp it.
	{
		
		for(i = 0;i < delta; i++)
		{
			result[biggest_size-size_of_second - i] = 
				first_value[size_of_first - size_of_second - i- 1];
		}
	
	}		
	
	if (carry)
	{
		for (i = 0;i < (delta)   ;i++)
		{
			ans=first_value[size_of_first - size_of_second - i - 1] + carry;
			carry = 0;
			if (ans > '9')
			{
				carry = 1;
				result[biggest_size-size_of_second - i]  = ans - 10 ;
			}
			else 
			{
				result[biggest_size - size_of_second - i] = ans ;
			}	
			
		}//end of for
		if (carry)
		{
			result[0]='1';
		}		
	}//end of if (exsitence of an carry
	
	return result;
}

int main(){

	char *num;
	num=add_two_postive_numbers("10","100");
	cout << num;
	delete [] num;
	return 0;
}