I'm currently studying differentiability at college, and I can't for the life of me understand how a constant is differentiable. I am using the definition of differentiability (as $h \rightarrow 0$ and you have $h$ at the bottom).

When $f(x) =c$ what is $f(x\_0 + h)?$ 

I understand why x is differentiable but I can't get a hold for constants! 

Thank you for reading!