Ошибка: unresolved external symbol - C++

#include "stdafx.h"
#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <ctime>
 
template <class InputIterator>
int SumOfRow(InputIterator begin, InputIterator end)
{
    int currentSum(0);
    while (begin++ != end) 
          currentSum += *begin;
    return currentSum;       
}
 
int main()
{
    srand(time(0));
    const std::size_t matrixSize(5);
    int matrix[matrixSize][matrixSize];
    
    std::cout << "Matrix: " << std::endl;
    for (unsigned i = 0; i < matrixSize; i++) {
        for (unsigned j = 0; j < matrixSize; j++)
            std::cout << std::setw(5) << (matrix[i][j] = rand() % 50);
        std::cout << std::endl;
    }
    
    int rowNumber(0);
    int maximalSum(SumOfRow(matrix[0], matrix[0] + matrixSize));
    for (unsigned i = 1; i < matrixSize; i++) {
        int currentSum(SumOfRow(matrix[i], matrix[i] + matrixSize));
        if (currentSum > maximalSum) {
                  maximalSum = currentSum;
                  rowNumber = i;
        }
    }
    std::cout << "Result: " << (rowNumber + 1) << std::endl;     
    
    return 0;
}

int factorial(int n); {
    if(n==1 || !n) return 1;
    return n* factorial (n-1); }
 
double expn(double x,double old_x, double eps, int n)
{
    if (!x) return 1.;
    double summ;
    if (n==1) summ = 1.;
    else summ = old_x;
    summ += pow(x,n)/(double)factorial(n);
    if (fabs(summ-old_x)>=eps)
        return expn(x, summ, eps, n+1);
    else return summ;
}