CalculatorIF.cpp
Modify it to include square rooting of each number.
Then modify it further to prevent square rooting of negative numbers.


Circle.cpp
Modify it so that if the user inputs a negative number for the radius,
the program displays a message saying the circumference and area are
not calculated.


Modify QuadraticFormula program so that it detects if the 'a'
coefficient is 0 or if the discriminant (b*b - 4ac) is negative.  In
either case we don't want to calculate the formula because it would
divide by zero if a is zero or do square root of a negative number if
the discriminant is negative, yielding Inf and NaN, respectively.