Thread: another homework question...

Looking for an improvement to my code. It's a little much to post, but here's the idea:

I have a class --"savingsAccount"--

in the main function I declare three objects with savingsAccount.

I'd like to loop through some functions on my savingsAccount objects "dynamically". That is, if I do a

for (i = 0, i <= 3, i++)

it works fine, but what if I add 3 more objects? I don't want to go change the for loop everytime an object is declared. My approach has been to add a static count to the class that is increased each time an object is declared. I can then loop from 0 to "< savingsAccount::count". good? bad? ideas?

Second half of the same problem is getting the object names inside the loop. if I have:

savingsAccount Saver1;
savingsAccount Saver5;
savingsAccount Saver7;
...

what can be done inside the for loop so that a different object is chosen each loop, and so I don't have to go change the for loop code when a new object is declared? I'm thinking there is a pointer solution here somewhere, but the solution has evaded me so far...

(mixed reply to both magos and elad)

OK... the terminoligy is starting to get just out of my reach...

I am guessing that "STL" is a collection of C++ classes available, but I am not familiar with those, and I suspect coming up with a solution provided by classes programmed outside of the scope of my *class* (acedemic here), would not be an acceptable solution.

yeah... loops 4 times. my bad, but it was just for an example. Thanks.

The pointer solution looks like it declares one pointer to an array of accounts... how would I reference the second account with that pointer?

I like that solution magos, but due to the restrictions on this assignment, I don't think that will work. The problem is we have multiple constructors. One object is declared with a name and balance in the data, one with only a name, and one with no name and no balance. I don't think I can use all three constructors when one array of savings accounts is declared... am I wrong?

STL is commonly used to refer to the Standard Template Library, and it is indeed a collection of classes for use in standardized C++ code, although many older compilers do not have it available as part of their software.

when arrays are declared using the new operator the new operator can only use the default constructor for the class.

Many people will say that the following lines declare an array of type savingsAccount on the heap(free store) using dynamic memory. The name of the array is MyPointer, and it has NrOfLoops elements within the array. Each element in MyPointer has been declared using the default constructor.

savingsAccount* MyPointer;
MyPointer=new savingsAccount[NrOfLoops];


Let's say you have three constructors for savingsAccount appropriate for the following examples:

int main()
{
savingsAccount savings1;
savingsAccount savings2("chelsea");
savingsAccount savings3("mercury", 4532);

const int MAX = 3;

savingsAccount Bank1[MAX];

Bank1[0] = savings1;
Bank1[1] = savings2;
Bank1[2] = savings3;

int i;
for(i = 0; i < MAX; i++)
{
cout << Bank1[i].name << " : " << Bank1[i].balance << endl;
}

cout << "now for a new bank. How many accounts to you want" << endl;
cin >> i;

savingsAccount * newBank = new savingsAccount[i];//uses default contstructor

int j;

//demonstrate that the default constructor was used in newBank
for(j = 0; j < i; j++)
{
cout << newBank[i].name << " : " << newBank[i].balance << endl;
}

//now get user input to put in newBank;
char dummy[80];
for(j = 0; j < i; j++)
{
cout << "enter name " << endl;
cin >> dummy;
strcpy(newBank[i].name, dummy);

cout << "enter balance" << endl;
cin >> newBank[i].balance;
}

//etc.

Originally posted by skillet
The problem is we have multiple constructors. One object is declared with a name and balance in the data, one with only a name, and one with no name and no balance. I don't think I can use all three constructors when one array of savings accounts is declared... am I wrong?

I believe you're right. Do you have to use constructors to init the data? You could use public functions:

Code:

savingsAccount* MyPointer;
int NrOfObjects=4;
MyPointer=new savingsAccount[NrOfObjects];
MyPointer[0].FakeConstructor1();
MyPointer[1].FakeConstructor2("Chelsea");
MyPointer[2].FakeConstructor1();
MyPointer[3].FakeConstructor3("Mercury", 4532);
...
delete[] MyPointer;

How about this.... I got this compiling, and the output is what I want. It is to a point now that it should be simple to add for loops at obvious locations--calculateNewBalance and cout. My class already contains a count of how many objects have been declared--each time I declare an object the total number of accounts is incremented, then I use that result for the account number.

I left out my class def... didn't think that is overly important. I overloaded "<<" to print out the data, and the functions are fairly self descriptive.

note:
It looked like I could have used "delete [] savingsPtr;" at the end, but it produces a warning at compile, since savingsPtr was not declared with a "new" assignment. Also, If I try to delete any of the pointers that were not assigned, it brings up a run-time error.



void main ()
{

// only limit to number of accounts is the array set here.
SavingsAccount *savingsPtr[10];

// 1) Declare 3 objects:
// Saver1: Margaret Olson with a balance of $2,000
// Saver2: Debra Baxter with no balance
// Saver3: account with no name, no balance
savingsPtr[1] = new SavingsAccount ("Margaret","Olson",2000.00);
savingsPtr[2] = new SavingsAccount ("Debra","Baxter");
savingsPtr[3] = new SavingsAccount;

// 2) Set Baxter's balance to $5,000
savingsPtr[2]->setBalance(5000.00);

// 3) Set Account 3 as "Arturo Ortiz"
// with a balance of $10,000
savingsPtr[3]->setName("Arturo","Ortiz");
savingsPtr[3]->setBalance(10000.00);

// 4) Calculate a new month balance for everyone
savingsPtr[1]->calculateNewBalance();
savingsPtr[2]->calculateNewBalance();
savingsPtr[3]->calculateNewBalance();

// 5) Show all the data for all of the accounts
fileout << *savingsPtr[1] << *savingsPtr[2] << *savingsPtr[3];

// 6) change the annual interest rate
SavingsAccount::setInterestRate(10.0);

// 7) Calculate a new month balance for everyone
savingsPtr[1]->calculateNewBalance();
savingsPtr[2]->calculateNewBalance();
savingsPtr[3]->calculateNewBalance();

// 8) Show all the data for all of the accounts
fileout << *savingsPtr[1] << *savingsPtr[2] << *savingsPtr[3];

// note: before dereferencing the pointers, the destructor
// was NOT called-- equals wasted memory.
delete savingsPtr[1];
delete savingsPtr[2];
delete savingsPtr[3];

}