Does lerp(a,b,C) automatically clamp C between 0 and 1?

...or do I need to use lerp(a,b,clamp(C,0,1)) for that to happen?

Why don't you just try?

If you set a text to lerp(0,50,2) you get 100..

Just guessing.... Maybe you are getting problems dealing with non-whole numbers? 0 and 1 is a hard one if you are using integers

If you are having problems with getting the fraction, you dont need to clamp anything. Just cast the variable into a float like this:

float(YourExpressionHere)

That will allow the decimal value that comes after the whole number.