Hey @mildlyeastern,

That's a great question! It's referred to as a ternary. It's a one line conditional statement where the condition is followed the truthy evaluation followed by the else. So like this:

condition == true ? ifConditionWasTrue : elseIfItWasNot

aka

if (condition == true) {
return ifConditionWasTrue;
}else{
return elseIfItWasNot
}

Can someone explain to me what the ? and the : does in the return statement.

This error stems from vectors having only 1 element or empty vectors. In that case numbers[1] has no meaning.