大数据乘法算法

#define _CRT_SECURE_NO_WARNINGS

#include <iostream>
#include <stdlib.h>
#include <string.h>
using namespace std;

struct bigdatacom
{
protected:
    char dataa[100];
    char datab[100];
public:
    void init(const char* str1, const char* str2)
    {
        cout << typeid(*this).name() << endl;
        strcpy(this->dataa, str1);
        strcpy(this->datab, str2);
    }
    char* getbigdata()
    {
        int lengtha = strlen(dataa);
        int lengthb = strlen(datab);
        int* pres = (int*)malloc(sizeof(int)*(lengtha + lengthb));
        memset(pres, 0, sizeof(int)*(lengtha + lengthb));
        //累乘
        for (int i = 0; i < lengtha; i++)
        {
            for (int j = 0; j < lengthb; j++)
            {
                pres[i + j + 1] += (dataa[i] - '0')*(datab[j] - '0');
            }
        }
        //进位
        for (int i = lengtha + lengthb - 1; i >= 0; i--)
        {
            if (pres[i] >= 10)//进位
            {
                pres[i - 1] += pres[i] / 10;//进位
                pres[i] %= 10;
            }
        }

        int i = 0;
        while (pres[i] == 0)
        {
            i++;
        }
        char* lastres = (char*)malloc(sizeof(char)*(lengtha + lengthb));
        int j;
        for (j = 0; j < lengtha + lengthb; j++, i++)
        {
            lastres[j] = pres[i] + '0';
        }
        lastres[j] = '\0';
        return lastres;
    }
};

struct myclass :public bigdatacom
{
    void coutstr()
    {
        cout << this->dataa << " " << this->datab << endl;
    }
};

void main()
{
    myclass class1;
    class1.init("12345", "1001");
    cout << class1.getbigdata() << endl;
    class1.coutstr();
}