CompoundInterest.java

Below is the syntax highlighted version of CompoundInterest.java from §9.1 Scientific Computation.

/******************************************************************************
 *  Compilation:  javac CompountInterest.java
 *  Execution:    java CompoundInterest a r n
 *
 *  Invest a pennies at annual interest rate r%, where interest
 *  is compounded n times per tear.
 *
 *  % java CompoundInterest 100000 5 365
 *  Exact: 105126.74964674473
 *  Round to nearest penny: 105110
 *  Round down to nearest penny: 104940
 *
 ******************************************************************************/

public class CompoundInterest {
   public static void main(String[] args) {
      int a = Integer.parseInt(args[0]);  // amount in pennies
      int r = Integer.parseInt(args[1]);  // annual interest rate in percent
      int n = Integer.parseInt(args[2]);  // compounding periods per year

      // compute using double precision arithmetic
      double amount1 = a * Math.pow(1 + r / 100.0 / n, n);

      // round to nearest penny
      long amount2 = a;
      for (int i = 0; i < n; i++)
          amount2 = Math.round(amount2 * (1 + r / 100.0 / n));

      // round down to nearest penny
      long amount3 = a;
      for (int i = 0; i < n; i++)
          amount3 = (long) (amount3 * (1 + r / 100.0 / n));

      StdOut.println("Exact: " + amount1);
      StdOut.println("Round to nearest penny: " + amount2);
      StdOut.println("Round down to nearest penny: " + amount3);
   }

}