Homework 6: Factorial Calculator

Let’s make a factorial calculator!

First of all, we have to know what a factorial number is. If you see a number that is accompanied by an exclamation sign, you’re seing a factorial number, that consists in a number multiplied by all the precedent integer numbers until reach one. For example, 6!= 65432*1 = 720.

Knowing that, we can proceed to elaborate the code. We are going to create a function, of type “long double”, which is in charge of calculating factorial numbers.

You can see what I did in the following code.

// Using long double to obtain big values of factorial numbers

#include <iostream>
#include <math.h>
using namespace std;

long double fact (long double n)
{
  long double R=n;
  if (n==0)
    {R=1;}
  for (n--; n>0; n--){
    {R*=n;}
  }
  return R;
}

int main()
{
  long double N;
  long double n;
  char C='Y';

  do
  {
    if (C!='Y' && C!= 'y')
      {cout << "\n\nInvalid choise! \nTry again"<< endl;}
    else
    {
      cout << "\nNon-negative integer: ";
      cin >> N;
      n = floor(N);

      if (N<0)
        {cout << "\nMATH ERROR! \nPlease, introduce a NON-NEGATIVE number\n\n" << endl;}
      else if (N!=0 && (N/n)!=1)
        {cout << "\nMATH ERROR!\nPlease introduce an INTEGER number!\n\n";}
      else
        {cout << "\n" << N << "! = " << fact(N) << "\n\n";}
    }

    cout << "\nDo you want to introduce another number?\n(Yes = Y / No = N)\n\n";
    cin >> C;

  } while (C!='N' && C!='n');

  cout << "\n\nHave a nice day!!\n\n\n";
  return 0;
}