//    
// Example 5.19. This program computes the amount of money in 
// the bank after a certain number of years. It also computes     
// how many years it would take to arrive at a given amount.   
// The bank compounds interest annually.   
//    
   
#include <iostream.h>
#include <math.h> 
#include "money.h"     
   
money ReadPrincipal(void);   
float ReadRate(void);   
   
int main(void)   
{   
   int   menu(void);       // prototypes
   void  FindAmount(void);   
   void  FindYears(void);   
   void  error(int choice);   

   int choice;            // menu choice 
      
   choice = menu();      
   switch (choice)   
   {   
      case 1:  FindAmount();   
               break;   
      case 2:  FindYears();   
               break;   
      default: error(choice);   
   }   

   return 0;
}   
   
//   
// This function prints a menu of choices, reads and    
// returns the user's integer choice, 1 or 2; all other   
// choices are in error.   
// Pre:  none   
// Post: Function has returned user's choice from the menu.   
//    
   
int menu(void)   
{   
   int choice;      // menu choice 
      
   cout << "This program makes savings computations for an\n";
   cout << "account with interest compounded annually, quarterly, monthly, \n";
   cout << "or continueously. It will\n";
   cout << "ask you the one-time deposit amount and the annual\n";
   cout << "interest rate. You have two choices: Given a number\n";
   cout << "of years, the program will return the final amount;\n";
   cout << "given a final amount, the program will tell the\n";
   cout << "number of years you must leave the money in the bank.\n\n";
   cout << "Choose from the following:\n\n";
   cout << "1. Given a number of years, calculate amount\n";
   cout << "2. Given a desired amount,  calculate years\n\n";
   cout << "Your choice: ";
      
   cin  >> choice;
   return choice;   
}   
   
//   
// This function obtains principal, interest rate, and years of   
// deposit; determines if an input error occurs; and if   
// not, calculates and prints final amount.   
//    amount = principal * (1 + rate)^years    
// Pre:  none   
// Post: If no errors, final amount has been displayed.   
//    
   
void FindAmount(void)   
{   
   int   ReadYears(void); // prototype  
   float rate;            // interest rate           
   int   years;           // number of years in bank 
   money principal,       // object for original deposit          
         ZeroDollars;     // object representing $0.00
         
   principal = ReadPrincipal();   
   rate      = ReadRate();   
   years     = ReadYears();   
      
   if (principal.LessThan(ZeroDollars)  ||
         principal.EqualTo(ZeroDollars) ||
         (rate <= 0)                    ||
         (years <= 0) )                     //error   
      cout << "\nInvalid input. Run program again.\n";
   else   
   {   
// compounding formular: A = P(1+r/n)^{nt}
// A: yield
// P: principal
// r: rate
// n: compound frequency in a year
// t: term in years
// when compounding continuesouly, n approaches infinity
//  A = P e^{rt}
      money p1, p2, p3;
      p1.AddTo(principal);
      p2.AddTo(principal);
      p3.AddTo(principal);

      principal.MultiplyBy(pow(1 + rate, years));   
      cout << "\nYou will have $";     
      principal.display();
      cout << " in the bank.\n";
      cout << "\nIf the interest is compounded monthly\n";
      cout << "You will have $";
      p1.MultiplyBy(pow(1 + rate/12.0, years*12.0));
      p1.display();
      cout << " in the bank.\n";
      cout << "\nIf the interest is compounded quarterly\n";
      cout << "You will have $";
      p2.MultiplyBy(pow(1 + rate/4.0, years*4.0));
      p2.display();
      cout << " in the bank.\n";
      cout << "\nIf the interest is compounded continueously\n";
      cout << "You will have $";
      p3.MultiplyBy(exp(rate*years));
      p3.display();
      cout << " in the bank.\n";
   }   
}   
   
//   
// This function obtains principal, interest rate, and amount   
// desired; determines if an input error occurs; and if   
// not, calculates and prints number of years needed.   
//    years = smallest integer greater than or equal to   
//       log(amount/principal)/log(1 + rate)    
// Pre:  none   
// Post: The number of years needed or an error message   
//       has been displayed.   
//    
   
void FindYears(void)   
{   
   money ReadAmount(void); // prototype  
   float rate;             // interest rate           
   int   years;            // number of years in bank 
   money amount,           // final amount in bank    
         principal,        // original deposit          
         ZeroDollars;      // object representing $0.00
   
   principal = ReadPrincipal();   
   rate      = ReadRate();   
   amount    = ReadAmount();   
         
   if ((!principal.LessThan(amount))     ||
         principal.EqualTo(ZeroDollars)  ||
         principal.LessThan(ZeroDollars) ||
         (rate <= 0))                       //error
      cout << "\nInvalid input. Run program again\n";
   else   
   {   
      years = (int)ceil(log(amount.quotient(principal)) 
                 / log(1 + rate));   
      cout << "\nYou will need the account for "     
            << years << " years.\n";
   }   
}   
   
//   
// This function reads and returns principal   
// Pre:  none
// Post: The money object for the principal was returned.   
//    
   
money ReadPrincipal(void)   
{   
   double deposit;  // principal as a double
   
   cout << "\nGive the original deposit: ";
   cin  >> deposit;
   money principal(deposit); // original deposit object
   return principal;   
}   
   
//   
// This function reads and returns interest rate, -1 in    
// case of error    
// Pre:  none   
// Post: Floating point interest rate has been returned, -1    
//       in case of error.   
//    
   
float ReadRate(void)   
{   
   float rate;            // interest rate 
   
   cout << "Give the interest rate as a decimal number\n";
   cout << "     For example, for 6.25% type 0.0625: ";
   cin  >> rate;
   if ((rate <= 0.0) || (rate >= 0.2))     // error 
      rate = -1;   
   return rate;   
}   
   
//   
// This function reads and returns years of deposit   
// Pre:  none   
// Post: Years of deposit have been returned.   
//    
   
int ReadYears(void)   
{   
   int years;      // number of years in bank 
   
   cout << "Number of years to leave in bank: ";
   cin  >> years;
   return years;   
}   
   
//   
// This function reads and returns the amount desired   
// Pre:  none   
// Post: The money object for the amount desired was returned.   
//    
   
money ReadAmount(void)   
{   
   double desired;  // amount desired
   
   cout << "Give the amount desired: ";
   cin  >> desired;
   money amount(desired); // object for amount desired 
   return amount;   
}   
      
//   
// This function prints an error message for an invalid   
// menu choice   
// Pre:  choice has an invalid value.   
// Post: Error message is displayed.   
//    
   
void error(int choice)   
{   
   cout << choice << " is an invalid choice. Please run again.\n";
}