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c#console-applicationcalculation
Lee Jaedong
Lee Jaedong

Reputation: 95

Calculating factorial using user input - console application

Edited: pasted the correct code this time...

I'm trying to calculate a factorial of a number. In this example, I enter the number 5.

Trying this method, gives me a huge negative number:

 static void Main(string[] args)
    {
        int consoleInput = int.Parse(Console.ReadLine());            

        for (int i = 1; i < consoleInput; i++)
        {
            consoleInput = consoleInput * i;
        }

        Console.WriteLine(consoleInput);
    }

Outputs -1899959296

However:

 static void Main(string[] args)
    {
        int consoleInput = int.Parse(Console.ReadLine());
        int result = consoleInput;

        for (int i = 1; i < consoleInput; i++)
        {
            result = result * i;
        }

        Console.WriteLine(result);
    }

Outputs 120

If I enter 5 both times, the first time the output is -1899959296 and the second time, the output is 120.

Can someone explain why?

Upvotes: 1

Views: 540

Answers (1)

Poul Bak
Poul Bak

Reputation: 10929

The problem is you change 'consoleInput' in each loop:

for (int i = 1; i < consoleInput; i++)
        {
            consoleInput = consoleInput * i;
        }

Now the 'for' checks against a new value every time.

The reason it gets negative is an overflow condition.

Edit:

The reason it gets so large, is because the loop 'never' ends, since the value you check against grows on every loop.

Upvotes: 5

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