[Dev-C++] Program critique

So, after a day of experimenting, I found out how to write a function
allowing me to double pennies.

Like in that old saying would you rather have a million dollars or a penny
doubled every day for a month?

 

I would like to know if anyone could suggest a better/ more efficient way to
accomplish what the program does.

I will work on using the loop in the function itself so as not to call the
pdt function every time, but for a newbie I wouldn't mind suggestions at
this point.

 

Thanks,

 

42 

 

 

#include <cmath>

#include <iostream>

#include <string>

using namespace std;

string next;

int pdt(int);

int prevd;

double long long prevt = 1;

int main(void)

      {

      do

    { prevd = 1;

      cout << "How many days?" ;

      int number;

      cin >>  number;

      cout << "For being good the tooth fairy doubles your pennies \n";

       for (int y=1;y!=number;++y)

      {   

          cout << "after " << y << " nights, you wake to find  ";

        

          cout << pdt(prevd) << " pennies for a total of ";

          prevt += prevd;

           cout << "$" << prevt/100 << "\n" ;

      

      }

   prevt=1;

  cout << "Again?";

  cin >> next;}

  while (next != "no");

}

 

   

 int pdt(int temp ) {

                

     

    prevd = temp * 2;

    return prevd;

    

    }