Karatsuba Implementation C++ - c++

Question

So I've decided to take a stab at implementing Karatsuba's algorithm in C++ (haven't used this language since my second coding class a life time ago so I'm very very rusty). Well anyhow, I believe that I've followed the pseudocode line by line but my algorithm still keeps popping up with the wrong answer.
x = 1234, y = 5678
Actual Answer: x*y ==> 7006652
Program output: x*y ==> 12272852
*Note: I'm running on a mac and using the following to create the executable to run c++ -std=c++11 -stdlib=libc++ karatsuba.cpp
Anywho, here's the code drafted up and feel free to make some callouts on what I'm doing wrong or how to improve upon c++.
Thanks!
Code:
#include <iostream>
#include <tuple>
#include <cmath>
#include <math.h>
using namespace std;
/** Method signatures **/
tuple<int, int> splitHalves(int x);
int karatsuba(int x, int y, int n);
int main()
{
int x = 5678;
int y = 1234;
int xy = karatsuba(x, y, 4);
cout << xy << endl;
return 0;
}
int karatsuba(int x, int y, int n)
{
if (n == 1)
{
return x * y;
}
else
{
int a, b, c, d;
tie(a, b) = splitHalves(x);
tie(c, d) = splitHalves(y);
int p = a + b;
int q = b + c;
int ac = karatsuba(a, c, round(n / 2));
int bd = karatsuba(b, d, round(n / 2));
int pq = karatsuba(p, q, round(n / 2));
int acbd = pq - bd - ac;
return pow(10, n) * ac + pow(10, round(n / 2)) * acbd + bd;
}
}
/**
* Method taken from https://stackoverflow.com/questions/32016815/split-integer-into-two-separate-integers#answer-32017073
*/
tuple<int, int> splitHalves(int x)
{
const unsigned int Base = 10;
unsigned int divisor = Base;
while (x / divisor > divisor)
divisor *= Base;
return make_tuple(round(x / divisor), x % divisor);
}

Answer 1

There are a lot of problems in your code...
First, you have a wrong coefficient here:
int q = b + c;
Has to be:
int q = c + d;
Next, the implementation of splitHalves doesn't do the work. Try that:
tuple<int, int> splitHalves(int x, int power)
{
int divisor = pow(10, power);
return make_tuple(x / divisor, x % divisor);
}
That would give you the "correct" answer for your input, but... that is not a Karatsuba method.
First, keep in mind that you don't need to "split in halves". Consider 12 * 3456. splitting the first number to halves mean a = 0, b = 12, while your implementation gives a = 1, b = 2.
Overall Karastuba works with arrays, not integers.