在数组 C++ 中将大字符串相乘

在这里，我有一个SafeArray(不是那么安全，但我的老师说这很好)类和一个bigint类。我的 bigint 类可以加减就可以了，但是当我尝试乘法函数时，它根本不打印任何内容，我尝试调试并逐步完成它，但我似乎无法弄清楚，一直在研究它一段时间，无可救药地卡住了。任何帮助将不胜感激。谢谢

#include <iostream>
using namespace std;
#include <algorithm>
template<typename Element>
class SafeArray
{
int size;
Element*Array;
Element def;
public:
SafeArray()                         //default constructor(with no parameter)
{
size = 10;
Array = new Element[size]();
}
SafeArray(int value)         //constructor with one int
{
size = value;
Array = new Element[value];
for (int i = 0; i < size; ++i)
Array[i] = 0;
}
~SafeArray() {
delete[] Array;
}                                       //destructor
SafeArray(const SafeArray& rhs) : size(rhs.size), Array(new Element[size]), def(rhs.def)
{
for (int i = 0; i < size; ++i )
Array[i] = rhs.Array[i];
}
SafeArray& operator=(SafeArray rhs)
{
std::swap(Array, rhs.Array);
std::swap(size, rhs.size);
std::swap(def, rhs.def);
return *this;
}
Element get(int pos)    const                 //get method
{
if (pos<0)
{
cout << "error";
}
return Array[pos];
}
void set(int pos, Element val)
{
if (pos<0)
{
cout << "error";
return;
}
if (pos >= size)
{
resize(pos + 1);
}
Array[pos] = val;
}
void resize(int new_size)
{
Element*temp = new Element[new_size];
for (int i = 0; i<size; i++)
{
temp[i] = Array[i];
}
delete[]Array;
Array = temp;
size = new_size;
}
void set_default(Element d)        //set_default
{
def = d;
}
int get_size()                       //get size
{
return size;
}
};
int size = 100; //for testing
class bigint
{
SafeArray<int> *arr;
public:
bool sign;
bigint()                                                   //initializes to zero
{
arr = new SafeArray<int>;
for(int i =0;i < size; i++)
arr->set(i,0);
}
void print()                                               //prints numbers without zeroes in front
{
bool start_num=false;
for(int i = 0;i <arr->get_size() ;i++)
{
if(arr->get(i)!=0 && start_num==false )
{start_num=true;
cout << arr->get(i);}
else if(start_num==true)
cout<<arr->get(i);
}
cout<<endl;
}
void assign(const bigint &A)                             //
{
for(int i=0;i<arr->get_size();i++)
{                                                            //Ways to initialize stuff
arr->set(i,A.arr->get(i));
}
}
void assign(string num)                                  
{
long len = num.length();
int j=arr->get_size()-1;
for(long i=len-1;i>=0;i--)
{
arr->set(j,num[i]-48);
j--;
}
}
void add_pos(const bigint &A)                                //add big ints
{
int carry=0;
for(int i=size-1;i>=0;i--)
{
int result = arr->get(i)+A.arr->get(i)+carry;
arr->set(i,result%10);
carry=result/10;
}
}
void sub_pos(const bigint &A)
{
int borrow=0;
for(int i=size-1;i>=0;i--)
{
int result = ((arr->get(i) - A.arr->get(i)-borrow));
if(result<0)
{
arr->set(i,result +10);
borrow = 1;
}
else
{
arr->set(i,result);
borrow = 0;
}
}
}

void multiply(const bigint &A)
{
for(int i=size-1;i>=0;i--)
{
int carry=0;
for(int j=size-1;j>=0;j--)
{
int product=((arr->get(i)*A.arr->get(j))+carry);
arr->set(i+j,product%10);
carry=product/10;
}
}
}
}
int main()
{
bigint a,b;
a.assign("1234");
b.assign("5678");
a.multiply(b);
a.print();
return 0;
}