Project Euler - Problem 4 - Largest palindrome product

p4_projecteuler.cpp

/* 
Project_4.cpp : Largest palindrome product
A palindromic number reads the same both ways. 
The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99.

Find the largest palindrome made from the product of two 3-digit numbers.
*/

#include <iostream>
using namespace std;

int main()
{
	int num, digit, n, largest = 0, i1,j1;
  //num is the multiplication, n is backup of num, digit is every digit of num, 
  //largest is result, i1 and j1 are numbers that are multiplied.
  
	for (int i = 100; i <= 999; i++) // all 3 digit numbers (i1)
	{
		for (int j = 100; j <= 999; j++) // all 3 digit numbers (j1)
		{
			int reverse = 0; // reversed number
			num = i * j;
			n = num;
			while (num != 0)
			{
				digit = num % 10;
				reverse = (reverse * 10) + digit;
				num /= 10;
			}
			if (n == reverse && n > largest) // "n > largest" is necessary. Delete and check the both results to see why.
			{
				i1 = i;
				j1 = j;
				largest = n;
			}
		}
	}

	cout << "Largest palindromic number: " << i1 << " x " << j1 << " = " << largest << endl;

    return 0;
}