find the area of a shape

Find Area Of Shape
Source: Tino Duong, 2003

Description:

Write a program to calculate the are of four basic geometric shapes:

Triangles = (Base* Height)/2
Squares = (Length*Width)
Rectangles = (Length *Width)
Circles = (2*3.14*Radius)

The menu should keep looping until the user chooses to quit.

Requirements:

Your program must preset a menu system for the user to choose which shape they want to calculate. It should then call the appropriate function.
Once you have calculated the area, display the complete information to the screen
Your program should continue looping until the user orders it to quit.
Your program should have error checking for valid user input

Your output should look similar to this:

    This program will calculate the area of a specified shape
    ---------------------------------------------------------

    1) Triangle
    2) Rectangle
    3) Square
    4) Circle
    5) Quit

    Please select a shape: 1

    Base: 12
    Height:90

    The Area is 540

    Please select a shape: 5
    Good bye.

Concepts:

Functions
Looping structures
Standard Input/Output

Additional Concepts:

Challenge:

Given the points (as [x,y] coordinates) of a polygon that may have anywhere from 3 to 10 sides, write a program to calculate the area.