# factorial create panic

In order to avoid this stack overflow our function needs to check the input and then if it is a negative number then report it. (I know, instead of i64 we could have used u64 which is an unsigned integer that would only allow non-negative numbers. but in other functions we might not be able to use the type-system for that. e.g. what if we expect a positive whole number larger than 2?

One way to avoid reaching stack overflow is to call panic! ourselves.

**examples/errors/factorial-create-panic/src/main.rs**

fn main() { for number in [5, 10, 0, -1, 3] { let fact = factorial(number); println!("{number}! is {fact}"); } } fn factorial(n:i64) -> i64 { if n < 0 { panic!("Cannot compute factorial of negative number"); } if n == 0 { return 1; } n * factorial(n-1) }

Please type in a number: 10 10! is 3628800 Please type in a number: 0 0! is 1 Please type in a number: -1 thread 'main' panicked at 'Cannot compute factorial of negative number', examples/errors/factorial_create_panic.rs:14:9 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace