Functions

Writing Functions (Hard Wired Values)

The future_value function in futval.cpp is flawed because the starting amount of the investment and the number of years are hard-wired.
Hard-wiring prevents reuse of functions:
- Computing the balance after 20 years.
- Computing the balance with a different interest rate.
We avoid hard-wiring values into functions by passing them in as additional parameters.
Functions are more valuable when they are reusable.

double future_value(double initial_balance, double p, int n)
{
   double b = initial_balance * pow(1 + p / 100, n);
   return b;
}