c# - Why does computing factorial of relatively small numbers (34+) return 0?

Question

int n = Convert.ToInt32(Console.ReadLine());
int factorial = 1;
    
for (int i = 1; i <= n; i++)
{
    factorial *= i;    
}
Console.WriteLine(factorial);

This code runs in Console Application, but when a number is above 34 the application returns 0.

Why is 0 returned and what can be done to compute factorial of large numbers?

Answer 1

You're going out of range of what the variable can store. That's effectively a factorial, which grows faster than the exponential. Try using ulong (max value 2^64 = 18,446,744,073,709,551,615) instead of int (max value 2^31 = 2,147,483,647) - ulong p = 1 - that should get you a bit further.

If you need to go even further, .NET 4 and up has BigInteger, which can store arbitrarily large numbers.