code blocks power function is not working in c

Question

i am using code block for learning c. my code is

#include
#include
int main()
{
  int x;
  x = pow(5,2);
  printf(\"%d\", x);
}

Out         


        

Answer 1

I suspect you have a naive implementation of pow in your libm (I get 25, as it should be). If that computes pow(x,y) as exp(y*log(x)) for positive x without checking for (small) integral exponents and treating them specially, you get

Prelude> 2 * log 5
3.2188758248682006
Prelude> exp it
24.999999999999996

a double result slightly smaller than 25, so when that is converted to int it is truncated to 24.

To check, assign the result of pow(i,j) to a double and print that out.

With hardcoded pow(5,2), the compiler (most likely, it's what gcc does even without optimisation) computes the result during compilation exactly.