double ldexp(double , int exp);

Returns x times 2 raised to n

compile in linux with: gcc ldexp.c -o ldexp -lm -Wall

#include <stdio.h> /* including standard library */
//#include <windows.h> /* uncomment this for Windows */
 
#include <math.h> /* including math library */
 
int main ( void ) 
{
 
  printf ("4.2 raised to 2 is %f\n", ldexp(4.2, 2));
  return 0;
}

 output:
 user@host:~$ ./ldexp 
 4.2 raised to 2 is 16.8000