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:

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/***************************************************************************
 *            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;
}

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