><>, 5 bytes

n*-10 

uses stack initialisation with the -v option, put your input variable there.

Try it online!

Or try the reversal

Explanation

n Prints whatever is on the stack as a number * Multiply the top 2 elements on the stack. There aren't 2 elements, so it crashes. -10 Never gets executed or reversed: 0 Push a 0 onto the stack 1 Push a 1 onto the stack - Subtract top 2 elements and push result (-1) * Multiply top 2 elements (-1 * -v)   n Print as number The code wraps around and executes again. It crashes on the * as there is only one item on the stack: -1. 

><>, 5 4 bytes

n-r0 

uses stack initialisation with the -v option, put your input variable there.

Try it online!

Or try the reversal

Explanation

n Prints whatever is on the stack as a number - Subtract the top 2 elements on the stack. There aren't 2 elements, so it crashes. r0  Never gets executed or reversed: 0 Push a 0 onto the stack r reverse the stack (now 0, -v) - Subtract top 2 elements and push result (0-v, ie negated) n  Print as number The code wraps around and executes again. It crashes on the - as there is only one item on the stack: 0. 

><>, 5 bytes

n*-10 

uses stack initialisation with the -v option, put your input variable there.

Try it online!

Or try the reversal

Explanation

n Prints whatever is on the stack as a number * Multiply the top 2 elements on the stack.   There aren't 2 elements, so it crashes. -10 Never gets executed or reversed: 0 Push a 0 onto the stack 1 Push a 1 onto the stack - subtract top 2 elements and push result (-1) * Multiply top 2 elements (-1 * -v) n Print as number 

><>, 5 bytes

n*-10 

uses stack initialisation with the -v option, put your input variable there.

Try it online!

Or try the reversal

Explanation

n Prints whatever is on the stack as a number * Multiply the top 2 elements on the stack. There aren't 2 elements, so it crashes. -10  Never gets executed or reversed: 0 Push a 0 onto the stack 1 Push a 1 onto the stack - Subtract top 2 elements and push result (-1) * Multiply top 2 elements (-1 * -v) n Print as number The code wraps around and executes again. It crashes on the * as there is only one item on the stack: -1. 

><>, 5 bytes

n*-10 

Try it online!

><>, 5 bytes

n*-10 

uses stack initialisation with the -v option, put your input variable there.

Try it online!

Or try the reversal

Explanation

n Prints whatever is on the stack as a number * Multiply the top 2 elements on the stack. There aren't 2 elements, so it crashes. -10 Never gets executed or reversed: 0 Push a 0 onto the stack 1 Push a 1 onto the stack - subtract top 2 elements and push result (-1) * Multiply top 2 elements (-1 * -v) n Print as number