interest...

//
//  main.cpp
//  C4
//
//  Created by Betsalel Williamson on 9/18/11.
//  Chapter 4:
//  Compute and output compound interest on $1000.00 for 10 years, at interest rates of 5%, 6%, 7%, 8%, 9% and 10%.
//
//  This piece of code contains more comments than usual because of the for loops and clever use of variables. They make things harder to remember down the road, so I documented why and how I did things.
//

#include <stdio.h>
#include <stdlib.h>

//  You can change the start and end interest rates to show interest rates above and below 10 percent.
#define START_INTEREST_RATE 5
#define END_INTEREST_RATE 10
#define ACCOUNTS ((END_INTEREST_RATE-START_INTEREST_RATE)+1)

int main (int argc, const char * argv[])
{
    double moneyInBank = 1000.00;
    int years = 10;

    int variableInterestRate; //  doubles as a counter
    int counter; //  a variable only for use in the for loops
    double bankAccount[ACCOUNTS]; //  will hold the money and interest

    //  add the 1000.00 to each bank account
    for (counter = 0; counter < ACCOUNTS; counter++) {
        bankAccount[counter] = moneyInBank;
    }

    //  this is the loop where I add the interest to the bank accounts from with the first account at %5 interest for 10 years until the sixth account with %10 interest.
    for (variableInterestRate  = START_INTEREST_RATE;
         variableInterestRate <= END_INTEREST_RATE;
         variableInterestRate++) {

        for (counter = 0; counter < years; counter++) {
            //  the position in the array can be found by subtracting the first counter variableInterestRate by 5.
            //  so when the counter is first run I will be at position 0, and will increment the array as the variableInterestRate increases.
            //  again I use the counter variableInterestRate to compute the current iteration of interest rate.
            //  its bad practice to use variables cleverly, but it works.
            bankAccount[variableInterestRate-START_INTEREST_RATE] += bankAccount[variableInterestRate-START_INTEREST_RATE]*(variableInterestRate*(.01));
        }
    }

    //  I used counter here even though I incremented the array with variableInterestRate in the previous loop. Counter has no connection to years or bankAccount, it's just a one use variable.
    for (counter = 0; counter < ACCOUNTS; counter++) {
        printf("$%.2f at %%%-2d interest for %d years = $%.2f\n",
               moneyInBank,
               (counter+START_INTEREST_RATE),
               years,
               bankAccount[counter]);
    }

    return EXIT_SUCCESS;
}