Whats the problem here?!

[process]

Oook..im asked to create a savings calculation program. using a user defined contructor to initialise the values & also to set the values. Prior to this I used to constructor to initialise the values to 0/0.0 ect & then i had set methods to assign the values. After reading the briefing no set methods were to be used!

soooo I moddifed my program but now the output calculations are wrong? and i cant see why :( ....can some 1 point me to where or why this is happening plz

-------------------------------------
Header
------------------------------------
class Savings{
private:
double Investment;
double Rate;
int Period;

public:
Savings(double InvIn, double RateIn, int PeriodIn);
double getFinalValue();
};
-----------------------------------------
Implementation
-----------------------------------------
# include "Savings.h"


Savings::Savings(double InvIn, double RateIn, int PeriodIn ){

Investment=InvIn;
Rate=RateIn;
Period=PeriodIn;
}


double Savings::getFinalValue(){

for (int i=0; i<=Period; i++) //int i=1 makes answer wrong aswell
Investment +=(Investment*Rate/100);
return Investment;
}

-----------------------------------------------------
main cpp
-----------------------------------------------------
# include <iostream.h>
# include <conio.h>
# include "Savings.h"


void main()
{
double Inv=0.0, Rate=0.0;
int Period=0;

cout<<"Investment = ";
cin>>Inv;

cout<<""<<endl;

cout<<"Yearly Interest Rate = ";
cin>>Rate;

cout<<""<<endl;

cout<<"Saving Duration(Years) = ";
cin>>Period;

Savings NewSavings(Inv, Rate, Period);//Create new object of the savings class
//& Assign data values...
clrscr(); //Clear the screen

cout<<"Investment(£):";
cout.width(29); //allign the values for tidiness
cout<<Inv<<endl;

cout<<"Yearly Interest Rate(%):";
cout.width(18);
cout<<Rate<<endl;

cout<<"Duration(Years):";
cout.width(27);
cout<<Period<<endl;

cout<<"Amounts to a final calculation of:";
cout.width(8);
cout<<"£"<<NewSavings.getFinalValue();
}
--------------------------------------------------------------------------

Was giving the correct answer before i changed it to remove the set methods. Now when im passing the values via paramater to the class the output answer is wrong wrong wrong
Oh why why why :confused:

[drkybelk]

Hi mate,

probably your formula is wrong:

for (int i=0; i<=Period; i++) //int i=1 makes answer wrong aswell

This actually iterates Period + 1 times, so if you calculate the value for a year (Period == 1) you iterate through the loop twice!

another tip: When initializing in a constructor, get used to use an initializer list. It's tidier and more efficient in most cases.

Savings::Savings(double InvIn, double RateIn, int PeriodIn )
: Investment(InvIn),
Rate(RateIn),
Period(PeriodIn)
{

}

and if you want to use some statndard values for initialization try this:

Savings::Savings(double InvIn = 100.0 /* in £ */, double RateIn = 0.05 /* 1 == 100% */, int PeriodIn = 10 /* in years */)
: Investment(InvIn),
Rate(RateIn),
Period(PeriodIn)
{

}

Cheers,

D

[drkybelk]

And another typo:
double literals in c/c++ are normally told apart from integer literals by a .0
You divide "Rate/100" which should be "Rate/100.0". There are some rules where you get away with such sloppiness because of automatic type conversion, but better be tidy there.

D

[process]

all fixed......
i assumed the windows calculator was itterating the +% ontop of the new sum from the oprevious +%

seems it wasnt!!!

Cheers for your help with the contructor initialisation & the itteration prob :WAVE:

[drkybelk]

I got this in my email:
not: 1% of 10 is 0.1 so your result is correct...

ok, ive fixed the itteration problem

for (int i=1; i<=Period; i++)
Investment +=(Investment*Rate/100);

that initialisation method is new to me & i have used it.Thanks :D

:Investment(InvIn),
Rate(RateIn),
Period(PeriodIn)
{
}

But the problem still here...My calculation above must be wrong?
ie: if i enter the following:

investment = 10
rate = 1%
period = 1
I get the answer 10.1
but it should be 11

:confused:
***************

[process]

ye lollol!..sorry that was a moment of thickness