Pennies

#include <stdio.h>
#include <cs50.h>
#include <math.h>

int main (void)
{
    int days = 0;
    int fDay = 0;
    long double total = 0;

    printf("Days in month: "); //ask how many days there are in the month
    days = get_int();
    while(days > 31 || days <28) //in case they do not input a valid number of days
        {
        printf("Please try again.\nDays in month: ");
        days = get_int();
        }

    printf("Pennies on first day: "); //ask how many pennies they are to receive on the first day
    fDay = get_int();

    while(fDay < 0)//in case a negative number is given by the user
        {
        printf("Please input a positive value. \nPennies on first day: ");
        fDay = get_int();
        }

    total = (fDay*(pow(2, days)))/100;
    printf("$%.2Lf \n", total);
}