Beginner C help

This function to estimate cos(x) based on given precision e exits after one repetition of the do/while loop. What's wrong here?

cos(x) ~= 1 – x^2/2! + x^4/4! -...+x^(2i)/(2i)!

float estim(float x, float e)
{
  float s = 1, t = 1;
  int  sg = 1, i = 1;
  do
  {
    t = s;
    if (sg) s -= (fpow(x, 2*i)/fact(2*i));
       else s += (fpow(x, 2*i)/fact(2*i));
    i++;
    sg = !sg;
  } while (abs(s-t)>e);
  return s;
}

Oops, the t = s; is vestigial and redundant.

float estim(float x, float e){
    return Math.cos(x);
}

Ok, I've helped him.
sg = -sg;

Use TRAH and FLASE constants to make your code more readable.

>>4
This way, it's going to oscillate between 1 and -1 without end!

abs(s-t)>e is not the right way to force a certain precision.  Calculate how many terms will get you the precision you need(my calculus is rusty but I know it can be done) then do that many iterations using a for loop. Or just make e indicate how many iterations to do and use a for loop.

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