乘以bigints c ++ [英] multiply bigints c++

问题描述

这是我的乘法算法，它是我的大num类的一部分。 arr是指向我为Safe可调整大小的数组创建的类的指针。 main（）显然是不完整的（只是把它放在那里以显示我的bigint类如何与我的乘法函数相关）我在这里真正需要的是修复我的算法或给出我如何解决它的建议。谢谢

This is my multiply algorithm that is part of my big num class. The arr is a pointer to a class that I created for a Safe resizable array. The main() is obviously incomplete(just put it there to show how my bigint class works in relation to my multiply function) What I really need here is a fix for my algorithm here or give my advice on how to fix it. Thanks

         void multiply(const bigint &A)
{
    bigint temp1; // bigint with value 0

    int carry = 0;
    int shift = 0;
    bigint temp2;
    for(int j = size-1; j >= 0; j--) //no member size in bigint
    {
        for(int i=size-1; i>=0; i--)
        {
            // bigint with value 0 and size: size + A.size
            int result = (arr->get(i)*A.arr->get(j)+carry);

            //if(size - shift - (i - size-1) >= 0)
                temp2.arr->set(size-i, result%10);


            carry=result/10;
        }
        shift++;
        temp1.add_pos(temp2);
    }
    this->assign(temp1);
}


                int main()
                {
                   a.assign (12345);
                   b.assign (12342357);
                   a.multiply (b);
                }

推荐答案

您显然已复制了类的add-methode并使其成倍增加-方法。但那不行。您只是将A的每个数字乘以arr的对应的数字。要进行乘法运算，您必须将A的每个数字乘以每个数字的arr！正如您在纸上所做的那样。



先在纸上试一试，然后相应地更正你的算法。

You have obviously copied the add-methode of your class and made it into a multiply-method. But that won't work. You are only multiplying each digit of A with the corresponding digit of arr. To do a multiplication you must however multiply each digit of A with each digit of arr! Just as you would do on paper.

Try it on paper first and then correct your algorithm correspondingly.

你也可以看看 Boost Multiprecision Library [< a href =http://www.boost.org/doc/libs/1_53_0/libs/multiprecision/doc/html/boost_multiprecision/intro.html\"target =_ blanktitle =New Window> ^ ]



最好的问候

Espen Harlinn

You could also take a look at the Boost Multiprecision Library[^]

Best regards
Espen Harlinn

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