Exponent Substitution

[kcbrown1]

I have to write a program that will calculate the monthly payment based on a total balance, APR, and finance period all of which are user inputs. My teacher gave us the equation payment = balance / (1 - (1 + interest)^-n / interest). N is the number of months the finance period will last. Here's the catch; we are not allowed to use the math library to access exponents so I really have no clue what to do. He said something about using a loop but gave no specifics so I'm flying blind.

[freddy92]

Create a function with parameters for a number and the exponent, then use a loop to multiply the number by itself however many times the exponent says.

[kcbrown1]

Sorry, I'm not entirely sure how to write that.

[bradw]

Show us how far you got, and we can help you get further.

[kcbrown1]

I've done nothing as far as the math but here's what I've written.



////////////////////////////////
// Keenan Brown //
// Lab 2 //
// banker //
// 27 September 2012 ///
////////////////////////////////////////////////////////////////////////
// This program will calculate monthly payments //
// based on the total balance, annual percentage rate, //
// and the how long payments will be made in months. //
////////////////////////////////////////////////////////////////////////

# include <iostream> // Needed for stream I/O

# include <cstdlib> // Needed for system command, "clear"

# include <iomanip> // Needed for fixed decimal position



using namespace std; // Simplifies cin and cout

int main()
{

///////////////////////////////
// Vraiable Declaration //
///////////////////////////////

float payment; // The calculated monthly payment

float balance; // The total amount to be financed

float apr; // The APR inputted by the user

float interest; // The monthly interest calculated from APR

int n; // The number of months to be financed

int choice; // The menu choice the user makes

system ("clear"); // System command to clear the screen


///////////////////////////////////
// User prompt and menu //
//////////////////////////////////

cout << "1. Calculate Loan Payments";

cout << "\n2. Quit" << "\n\t";

cin >> choice;

///////////////////
// User menu //
///////////////////

interest = apr / 12 / 100; // Math to calculate monthly interest from APR

if (choice == 1)
{

do
{

cout << setprecision(2) << fixed; // Sets all decimal points to 2 places

cout << "\n\nHow much are you financing?\n\t";

cin >> balance;

cout << "\n\nHow long is the finance period in months?\n\t";

cin >> n;

cout << "\n\nWhat is the APR for this finance?\n\t";

cin >> apr;

/////////////////////////////////////
// User prompt and storage //
/////////////////////////////////////


cout << "\nBalance: $" << balance;

cout << "\nAPR: " << apr << "%";

cout << "\nMonthly interest: " << apr / 12 << "%";

cout << "\nTerm: " << n << " months";

cout << "\n\nCalculated monthly payment: $" << payment;

/////////////////////////////////////////////////////
// Display of user inputs and calculation //
////////////////////////////////////////////////////


cout << "\n\nPress ENTER to continue.";

cin.get( );

cin.ignore (1, '\n');

/////////////////////////////////////////////////////////////////
// Pauses program until user chooses to continue //
/////////////////////////////////////////////////////////////////

}

while (choice = 1);

}

else if( choice == 2)
{

cout << "\n\nGood day.\n\n";

}

return 0;

}