How can I multiply really big numbers c++

Question

I have the following code

      int i, a, z;
i = 2343243443;
a = 5464354324324324;
z = i * a;
cout << z << endl;

When these are

Answer 1

I would like to elaborate on, and clarify Shravan Kumar's Answer using a full-fledged code. The code starts with a long integers a & b, which are multiplied using array, converted to a string and then back into the long int.

#include 
#include 
#include

using namespace std;

int main()
{
//Numbers to be multiplied
long a=111,b=100;

//Convert them to strings (or character array)
string arr1 = to_string(a), arr2 = to_string(b); 

//Reverse them
reverse(arr1.begin(), arr1.end());
reverse(arr2.begin(), arr2.end());

//Getting size for final result, just to avoid dynamic size
int ans_size = arr1.size() + arr2.size();

//Declaring array to store final result
int ans[ans_size]={0};

//Multiplying 
//In a reverse manner, just to avoid reversing strings explicitly 
for(int i=0; i int)
        int p = (int)(arr1[i]) - '0';
        int q = (int)(arr2[j]) - '0';

        //Excerpt from Shravan's answer above
        ans[i+j]+=p*q;
        ans[i+j+1]=ans[i+j+1]+ans[i+j]/10;
        ans[i+j]%=10;
    }
}

//Declare array to store string form of final answer
string s="";

for(auto i=0;i