Question

I have some function,

int somefunction( //parameters here, let's say  int x) {
    return something  Let's say x*x+2*x+3 or does not matter
}

How do I find the derivative of this function? If I have

int f(int x) {
    return sin(x);
}

after derivative it must return cos(x).

Answer 1

You can approximate the derivative by looking at the gradient over a small interval. Eg

const double DELTA=0.0001;
double dfbydx(int x) {
  return (f(x+DELTA) - f(x)) / DELTA;
}

Depending on where you’re evaluating the function, you might get better results from (f(x+DELTA) - f(x-DELTA)) / 2*DELTA instead.

(I assume ‘int’ in your question was a typo. If they really are using integers you might have problems with precision this way.)