# Fundamentals of Programming: Constant Definitions

 Example: Declaring pi as a constant ```Const pi as Single = 3.14 console.writeline(pi) ```    Code Output 3.14
 Exercise: Constants Write a program that works out the area and circumference of a circle, setting pi to a constant. Use the equations: area = Πr2 and circumference = 2Πr For example:    Code Output Insert radius: 5 area = 78.5398163 circumference = 31.4159265 Answer: ```const pi as single = 3.14 dim r as single console.write("Insert radius: ") r = console.readline() console.writeline("area = " & pi * r * r) console.writeline("circumference= " & 2 * pi * r) console.readline() ``` Write a program that works out the cost of two clothing items showing the price, VAT, and price inclusive of VAT. VAT = 17.5%. For example    Code Output Insert price of item 1: 10.40 Insert price of item 2: 19.99 item 1 = 10.40 + 1.82 VAT = £12.22 item 2 = 19.99 + 3.49825 VAT = £23.48825 Answer: ```const VAT as single = 0.175 dim price1, price2 as single console.write("Insert price of item 1: ") price1 = console.readline() console.write("Insert price of item 2: ") price2 = console.readline() console.writeline("item 1 = " & price1 & " + " & price1 * VAT & " VAT = £" & price1 * (VAT + 1)) console.writeline("item 2 = " & price2 & " + " & price2 * VAT & " VAT = £" & price2 * (VAT + 1)) console.readline() ``` Why might you want to use a constant in your code instead of a normal variable? Answer: Constants are fixed values, so you can't accidentally assign them new values in other parts of your code. When is it suitable to use a constant? Answer: When you are using a value that doesn't need to change at run time and will be used in more than one location.