Calculating factorials

[Matome]

Hi everyone

So I was trying out this other exercise where I wrote a program that calculates the factorial of an integer, and so I managed to get that part right:

//File: calculatingfactorials.cpp
#include <iostream>
using namespace std;
int main (void)
{
int K;
int factorial;

factorial = 1;

cout << "Enter an integer: ";
cin >> K;

CHECK:
if (K > 0)
{
factorial = K * factorial;
K = K - 1;
goto CHECK;
}
else
cout << factorial << "\n";
}

I am now supposed to modify the code so that if I enter a number that is not an integer, e.g. -3, it will output that "Factorial cannot be calculated" and I do not know where to even begin the modifications, so any help please.

Kind regards
Matome

[giblit]

Use an if statement. Also -3 is an integer it's just a signed instead of unsigned integer. Do something like:

if integer >= 0
     return factorial
else
    return error code

[Stormboy]

Make a function called factorial. Use if statements to check whether a positive number is given or not. If yes, then use recursion to find the factorial (return n*factorial(n-1);). Otherwise, return -1. In your main code, check the return value. If its positive, print the return value as its the factorial. If its -1, print the error.
This may sound a bit complicated but its not.

[Matome]

I get what you are both saying, but it still doesn't seem to work

[Stormboy]

What do you mean by it doesn't seem to work? Do you get any errors or something? Can you please post your new code?

[Matome]

Or maybe I just didn't full understand

//File: test.cpp
#include <iostream>
using namespace std;
int main (void)
{
int K;
int factorial;

factorial = 1;

cout << "Enter an integer: ";
cin >> K;

CHECK:
if (K >= 0)
return factorial;

else
return "error code";
}

Please bear with me, this is my first year of ever programming.

[giblit]

You were supposed to fill in the factorial and error code with the factorial/error code :P



there are many ways to get factorials. a simple way would be recursion or you could use a loop. like:

[code]int factorial = 1; 
for(int i = 2; i <= n; ++i)
{
    factorial *= n;
}
//factorial of 0 or 1 is 1
//so it's fine that they won't be in the loop 

Then the error code could be return -1; and/or a message like std::cerr << "Error: you can not get the factorial of a negative number." << std::endl;

[Matome]

Ok thanks :-D...it worked