Beginning C# 3.0

A.9. Chapter 11

A.9.1. Exercise 1 Solution

The error message is:

Use of unassigned local variable 'x'

The problem is that C# doesn't want you to return a variable that has not been explicitly assigned a value. In the code, x is assigned a value only when the if statement is true. To fix the problem, you must explicitly assign x a value. The easiest fix is to change the definition of x:

int x = 0;

A.9.2. Exercise 2 Solution

The issue here is not whether you can code the equation correctly, but whether you can make it readable for others. The first solution might be

p = a  * 1 / (Math.Pow(1 + i, y));

The code would compile and generate the correct values for p. However, which would you rather debug: the preceding statement or the following?

presentValue = futureAmount  * 1.0 / (Math.Pow(1.0
+ interestRate, yearsIntoFuture));

The primary difference is the use of meaningful variable names. Another benefit is the use of numeric constants (1.0) that reflect the fact that floating-point values are being used in the equation. You could make the argument that the decimal data type should be used since this is a financial calculation. However, the pow() method uses the double data type, so I would probably stuff this equation into a method that returned a double and let the user decide to cast it to a decimal if needed.

An alternative that makes debugging a bit easier would be:

discountFactor = 1.0 / (Math.Pow(1.0 + interestRate, yearsIntoFuture)); presentValue = futureAmount * discountFactor; ...