What is wrong with the following code?

Question

//A program that calculates the amount of money in a bank account after n years

#include <stdio.h>

double bank(double money, double apy, int years);

int main() {

double money1, apy1;
int years1;

printf("How much money is currently in your bank account? ");
scanf("%d", &money1);

printf("How many years will this money stay in your account? ");
scanf("%d",&years1); 

printf("What is your APY? ");
scanf("%d", &apy1); 

int bank1 = bank(money1, apy1, years1);

printf("Your grand total after %d will be $%d \n", years1, bank1); 


system ("PAUSE");
return 0;   
}


double bank(double money, double apy, int years) {

 if(years <= 0) 
    return money;

 else
    return bank(money*apy, apy, years-1);

 }

Seriously? "What is wrong with this code?" is your entire "question"? — John Parker
– John Parker, Commented Jan 24, 2011 at 21:54
Is it not compiling? Is it failing in some other way? I'm afraid you'll have to be more specific. — Doug T.
– Doug T., Commented Jan 24, 2011 at 21:54
@Krysten you might want to edit your question to ask exactly why its not calculating the total correctly. — Doug T.
– Doug T., Commented Jan 24, 2011 at 21:58

Paul R · Accepted Answer · 2011-01-24 21:58:02Z

4

Change:

scanf("%d", &money1);

to

scanf("%lf", &money1);

and change:

scanf("%d", &apy1);

to:

scanf("%lf", &apy1);

And while you're at it you might want to add some printfs to help with debugging (assuming you don't have a source level debugger.)

answered Jan 24, 2011 at 21:58

Paul R

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Comments

casablanca · Accepted Answer · 2011-01-24 21:55:40Z

4

This:

return bank(money*apy, apy, years-1);

should probably be

return bank(money*(1+apy), apy, years-1);

since the interest you earn should be added to the existing amount. Otherwise your total amount would be reducing each year.

answered Jan 24, 2011 at 21:55

casablanca

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2 Comments

James Over a year ago

Also the return from bank is being cast to int but I'm not sure if this is deliberate or not.

kachilous Over a year ago

that doesn't seem to give me the desire output

user418748 · Accepted Answer · 2011-01-24 21:58:12Z

2

Another one is :

double bank(double money, double apy, int years);

Returns a double, but

int bank1 = bank(money1, apy1, years1);

You place the result in an int.

answered Jan 24, 2011 at 21:58

user418748

Comments

Community · Accepted Answer · 2017-05-23 11:55:29Z

1

You should never use floating point in financial calculations.

Floating point is inherently uncapable of representing 10-base values precisely, which means that you will suffer from rounding errors and unequalities, which is unacceptable in finances (among others).

This has been discussed in detail many times on SO. The issue is not language specific.

edited May 23, 2017 at 11:55

CommunityBot

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answered Jan 24, 2011 at 21:58

Péter Török

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Comments

Elalfer · Accepted Answer · 2011-01-24 21:57:58Z

0

I think you should call you function in the following way:

int bank1 = bank(money1, 1+apy1/100., years1);

Otherwise you'll have a LOT of money :)

answered Jan 24, 2011 at 21:57

Elalfer

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