Loop Problem

[josh26757]

I am in college for programming, but my programming classes do not start until January. I am trying to work on C++ to get ready for my classes. I am currently in Personal Finance class and was intrigued by an interest calculator. I am not done the code because I need to add the compound interest section in the final loop. The problem I can't seem to fix is updating the minimum payment after each monthly payment. I also need to section off the part that chooses a set payment or a minimum payment. I just wanted to point out I am aware of this and know I need to fix it.

The problem: If I add payment=total*MinInterest(this is defined as .03 for 3&#37 then the loop gets stuck. I also used the math::ceil() for the wrong reason. I was trying to find a way to trim the double variables down to two decimal places(0.00) Can someone explain why I am having the loop problem and what I need to work on as far as code. I take all your advice very seriously and am anxious to learn. Here is the code.
BTW I am using DEV-C++

#include <cstdlib>
#include <iostream>
#include "math.h"
#define year 12
#define MinInterest .03
#define DaysInCycle 30

using namespace std;
// Displays Program Header
void menu()
{
   cout<<"@@@@@@@@@@@@@@@@@@@@\n"
       <<"@                  @\n"
       <<"@   Credit         @\n"
       <<"@    Card          @\n"
       <<"@     Payoff       @\n"
       <<"@      Calculater  @\n"
       <<"@                  @\n"
       <<"@@@@@@@@@@@@@@@@@@@@\n";
       
}  
//Gets Bill Total
double bill_total()
{
 double total;
 system("CLS");
 menu();
 cout<<"Please Enter The Total Amount:";
 cin>>total;
 total=ceil(total);
 return total;
}
// Gets APR
double APR()
{
  system("CLS");
  menu();
  double APR;
  cout<<"Please Enter APR:";
  cin>>APR;
  APR=ceil(APR);
  return APR;
}
//Gets User's Payment If PaymentSelection == 2
double GetPayment()
{
  double ammount;
  system("CLS");
  menu();
  cout<<"Please Enter Payment Ammount:";
  cin>>ammount;
  return ammount;
}
//Calculates Minimum Payment
double CalculateMinPayment(int total)
{
  return (total*MinInterest);
}
//User Selects Set Ammount Or Minimum Payment Style
double PaymentSelection(int total)
{
  int choice;
  do{
  system("CLS");
  menu();
  cout<<"1.Minimum Payment 2.Set Payment\n";
  cin>>choice;
  if(choice==1)
  return CalculateMinPayment(total);
  else if(choice==2)
  return GetPayment();
  }while(choice!=1||choice!=2);
}
//Finale Calculation
void calculate(double APR,double Payment,double Total)
{
  //initilize
  double TotalInterest=0,MonthlyInterest=0,Principal=0,AverageDailyBalance=0,TotalPaid=0;
  double month=1.0;
  
  //loop tell total is paid
  while(Total>0){
  //calculate monthly APR
  APR=ceil(APR);
  //calculate monthly interest
  MonthlyInterest=(APR/year)/100;
  //calculate Average Daily Balance
  AverageDailyBalance=Total/DaysInCycle;
  //Find Total Interest Paid
  TotalInterest=AverageDailyBalance*MonthlyInterest;
  //round total interest
  TotalInterest=ceil(TotalInterest);
  //Calculate principal paid
  Principal=(Payment-TotalInterest);
  //Calculate total for next month bill
  Total=(Total-Principal);
  //Keep track of total paid
  TotalPaid=TotalPaid+Payment;
  month++;}
  
  system("CLS");
  cout<<"It will take you "<<(month/12)<<" years to pay off the ammount.\n";
  cout<<"And it will cost you "<<TotalPaid<<"$"<<" total\n";
  
}
int main(int argc, char *argv[])
{
   menu();
   double total=bill_total();
   calculate(APR(),PaymentSelection(total),total);
   system("PAUSE");
   return EXIT_SUCCESS;
}

[GCDEF]

I couldn't compile it. You may want to check the type on the function parameter called total that you're passing around. In main it's a double, but you're passing it as an int. I'm surprised your compiler isn't complaining.

[josh26757]

ooops
I had made a change while testing. It is fixed now. Thanks for the quick response!

[josh26757]

The compound interest is not there is why it will come out as 5100$ Just go to the main loop in Calculate and add

Payment=Total*MinInterest;

I added

cout<<Payment<<" "<<month<<endl;

to the end of the loop as well and the .00000 digits seems to be causing the problem. I do not understand why. The MinInterest is always .03. Maybe I am being stupid, but I do not understand what is going on.

[josh26757]

BTW-Let me know what looks wrong in my programming grammar. Is my code formatted OK? What should I be working on?
I am currently working on Algorithms and data logic when I have time.

[GCDEF]

Isn't your compiler giving you warnings? I changed total from int to double but I'm still getting warning C4700: uninitialized local variable 'TotalPaid' used

Get rid of all the warnings and try again.

Formatting wise, use some white space.

Instead of
TotalInterest=AverageDailyBalance*MonthlyInterest;

TotalInterest = AverageDailyBalance * MonthlyInterest;

That seems much easier on the eye to me.

[josh26757]

I am not getting any warnings?
TotalPaid is initialized at the beginning of calculate() What line is showing the error?

[Paul McKenzie]

I am not getting any warnings?

What compiler are you using? Brand and version?

Regards,

Paul McKenzie

[Lindley]

I was trying to find a way to trim the double variables down to two decimal places(0.00)

Usually you should do this via output formatting rather than actually modifying the value of the variable.

However, you should also be aware that financial code is generally supposed to use integer math since it's exact (counting cents or tenths of cents), whereas floating point math is approximate. This doesn't really matter for a toy program but keep it in mind.

[GCDEF]

I am not getting any warnings?
TotalPaid is initialized at the beginning of calculate() What line is showing the error?

You changed your code since your OP. I still get two warnings with VC2008 with the code you currently have.

You're still passing a double as an int apparently.

(110) : warning C4244: 'argument' : conversion from 'double' to 'int', possible loss of data
(73) : warning C4715: 'PaymentSelection' : not all control paths return a value

[josh26757]

Usually you should do this via output formatting rather than actually modifying the value of the variable.

However, you should also be aware that financial code is generally supposed to use integer math since it's exact (counting cents or tenths of cents), whereas floating point math is approximate. This doesn't really matter for a toy program but keep it in mind.

Interesting,
If you do not mind give me an example of using integer math. I may be misunderstanding you but how do I get cents with an integer( I am such a noob).

[josh26757]

You changed your code since your OP. I still get two warnings with VC2008 with the code you currently have.

You're still passing a double as an int apparently.

(110) : warning C4244: 'argument' : conversion from 'double' to 'int', possible loss of data
(73) : warning C4715: 'PaymentSelection' : not all control paths return a value

Does this fix it?

#include <cstdlib>
#include <iostream>
#include "math.h"
#define year 12
#define MinInterest .03
#define DaysInCycle 30

using namespace std;
// Displays Program Header
void menu()
{
   cout<<"@@@@@@@@@@@@@@@@@@@@\n"
       <<"@                  @\n"
       <<"@   Credit         @\n"
       <<"@    Card          @\n"
       <<"@     Payoff       @\n"
       <<"@      Calculater  @\n"
       <<"@                  @\n"
       <<"@@@@@@@@@@@@@@@@@@@@\n";
       
}  
//Gets Bill Total
double bill_total()
{
 double total;
 system("CLS");
 menu();
 cout << "Please Enter The Total Amount:";
 cin >> total;
 total = ceil(total);
 return total;
}
// Gets APR
double APR()
{
  system("CLS");
  menu();
  double APR;
  cout << "Please Enter APR:";
  cin >> APR;
  APR = ceil(APR);
  return APR;
}
//Gets User's Payment If PaymentSelection == 2
double GetPayment()
{
  double ammount;
  system("CLS");
  menu();
  cout << "Please Enter Payment Ammount:";
  cin >> ammount;
  return ammount;
}
//Calculates Minimum Payment
double CalculateMinPayment(double total)
{
  return (total*MinInterest);
}
//User Selects Set Ammount Or Minimum Payment Style
double PaymentSelection(double total)
{
  int choice;
  do{
  system("CLS");
  menu();
  cout << "1.Minimum Payment 2.Set Payment\n";
  cin >> choice;
  if(choice==1)
  return CalculateMinPayment(total);
  else if(choice==2)
  return GetPayment();
  }while(choice!=1||choice!=2);
} 
//Finale Calculation
void calculate(double APR, double Payment, double Total)
{
  //initilize
  double TotalInterest=0, MonthlyInterest=0, Principal=0, AverageDailyBalance=0, TotalPaid=0;
  double month=1.0;
  
  //loop tell total is paid
  while(Total>0){
  //calculate monthly APR
  APR = ceil(APR);
  //calculate monthly interest
  MonthlyInterest = (APR/year) / 100;
  //calculate Average Daily Balance
  AverageDailyBalance = Total / DaysInCycle;
  //Find Total Interest Paid
  TotalInterest = AverageDailyBalance * MonthlyInterest;
  //round total interest
  TotalInterest = ceil(TotalInterest);
  //Calculate principal paid
  Principal = (Payment-TotalInterest);
  //Calculate total for next month bill
  Total = (Total-Principal);
  //Keep track of total paid
  TotalPaid = TotalPaid + Payment;
  month++;}
  
  system("CLS");
  cout<<"It will take you "<<(month/12)<<" years to pay off the ammount.\n";
  cout<<"And it will cost you "<<TotalPaid<<"$"<<" total\n";
  
}
int main(int argc, char *argv[])
{
   menu();
   double total = bill_total();
   calculate(APR(),PaymentSelection(total),total);
   system("PAUSE");
   return EXIT_SUCCESS;
}

[GCDEF]

Does this fix it?

Doesn't fix not all control paths return a value.

[VladimirF]

I think you undercharge the interest:

//calculate Average Daily Balance
AverageDailyBalance=Total/DaysInCycle;
//Find Total Interest Paid
TotalInterest=AverageDailyBalance*MonthlyInterest;

I wish my credit cards worked that way!

[GCDEF]

I don't get stuck in any loop. What is the problem and how do we recreate it? Have you tried the debugger?