Project Euler - Problem 8 - Largest product in a series

p8_projecteuler.cpp

/* 
Project_8.cpp : Largest product in a series
The four adjacent digits in the 1000-digit number 
that have the greatest product are 9 × 9 × 8 × 9 = 5832.

73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450

Find the thirteen adjacent digits in the 1000-digit number that have 
the greatest product. What is the value of this product?
*/

#include <iostream>
#include <fstream>
#include <vector>
using namespace std;

int main()
{
	size_t size = 1000; //size of array 1000
	vector<int> num(size); //dynamic array

	ifstream inFile;
	inFile.open("number.txt"); //open the file

	if (inFile.is_open())
	{
		char n1;
		int n, i = 0;
		while (inFile.get(n1)) // reading every char in file
		{
			if (n1 != 10) // as there are "line feed" (\n), we exclude that
			{
				n = n1 - 48; // converting char to int
				num[i] = n; // assigning digits to the array
				i++;
			}
		}
	}
	else
		cerr << "Error opening file!" << endl;

	inFile.close();

	long long greatest = 0; // type is long long as it can exceed int range
	for (int i = 0; i < 988; i++) // imagine num[987+12] = num[999]
	{
		long long temp = 1; // same reason
		for (int j = 0; j < 13; j++)
		{
			temp *= num[i + j]; // multiplying 13 adjacent digits
		}
		if (temp > greatest)
		{
			greatest = temp;
		}
	}

	cout << "Greatest product of thirteen adjacent digits is " << greatest << endl;
	

    return 0;
}

// HELL OF A PROBLEM!
// TOOK ME 3/2 HOURS TO SOLVE BUT IT'S WORTH IT !!!