Decision Making and Looping

The program uses a for loop to print the "Powers of 2" table for the power 0 to 20. both positive and negative.

#include <stdio.h>
void main()
   {
       long int p;
       int      n;
       double   q;
       printf("------------------------------------------\n");
       printf(" 2 to power n       n       2 to power -n\n");
       printf("------------------------------------------\n");
       p = 1;
       for (n = 0; n < 21 ; ++n)    /* LOOP BEGINS */
       {
    if (n == 0)
       p = 1;
    else
       p = p * 2;
    q = 1.0/(double)p ;
    printf("%10ld %10d %20.12lf\n", p, n, q);
       }                           /* LOOP ENDS   */
       printf("------------------------------------------\n");
       getch();
   }