CODEWITHSUNDEEP
c++
Ds Ss
Ds Ss

Reputation: 19

why is the error in this program c++?

I don't understand this program, I don't get why number is initialized to 1 when the program takes user input. This is how I understand the program which is obviously wrong:

You enter the factorial number, lets says I enter 6, it goes to the while loop because 6 is greater than 1. Now factorial is 1, and number is 6, 6 * 1 = 6. Then 6 - 1 = 5, so factorial is 5 but i get 720 as output.

i don't think I understand the while loop

#include <iostream>
using namespace std;

int main()
{
    // declaration of the variables
    int factorial, number;

    // initialization of the variables
    factorial = 1;
    number = 1;

    // Prompt the user to enter the upper limit of integers
    cout << "Please enter the number of the factorial";
    cin >> number;

    // using the while loop find out the factorial
    while (number > 1)
    {
        factorial = factorial * number;
        number = number - 1;
    }
    cout << "The factorial is " << factorial;
}

Upvotes: 0

Views: 136

Answers (5)

Splitlocked
Splitlocked

Reputation: 761

The first thing I noticed was that there is an error in your code:

cout<<"The factorial is " < factorial;

should be:

cout<<"The factorial is " << factorial;

Correcting this should fix a compile error.

The essence of this code is:

  1. Get a number (int number) from user
  2. Print print the factorial of number

Upvotes: 0

Kerrek SB
Kerrek SB

Reputation: 476920

The initial assignment of number is indeed unnecessary. However, you should check the input operation for errors:

int factorial = 1;
int number;

if (!(std::cin >> number))
{
    /* error! */
    return 1; // i.e. abort the program
}

while (number > 1) { /* ... */ }

Upvotes: 1

m0skit0
m0skit0

Reputation: 25863

Your program works correctly. 

6! = 6 * 5 * 4 * 3 * 2 = 720.

Btw, use recursion for such recursive problems.

#include <iostream>

using namespace std;

int main()
{

    //declaration of the variabe
    unsigned int number;

    //prompt the user to enter the upper limit of integers
    cout << "Please enter the number of the factorial";
    cin >> number;

    cout << factorial(number);

    return 0;
}

unsigned int factorial(unsigned int n)
{
    if (n <= 1)
    {
        return 1;
    }
    else
    {
        return n * factorial(n-1);
    }
}

Upvotes: 2

binW
binW

Reputation: 13672

You are missing a "<" in last line of the program. It should be

cout<<"The factorial is "<<factorial;

After making this change when I compile and run the program it works for me correctly i.e computes the correct factorial. For example factorial of 5 i.e 5!=5*4*3*2*1=120

Upvotes: 2

Adel Boutros
Adel Boutros

Reputation: 10285

First of all, it is initialised to 1 because of the following condition:

Factorial(0) = 1
Factorial(1) = 1

So if a user inputs a number less than 2, you do not need some calculations, you just output 1

Upvotes: 0

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