Since I was 12, I was always wondering how I can make a function which calculates the power (e.g. 2³) myself. In most languages these are included in the standard library, mostly as pow(double x, double y), but how can I write it myself?

I was thinking about for loops, but it think my brain got in a loop (when I wanted to do a power with a non-integer exponent, like 5^4.5 or negatives 2^-21) and I went crazy ;)

So, how can I write a function which calculates the power of a real number? Thanks