1. Practical Programming COMP153-08S Arithmetic and Types

2. Admin – room changes COMP153-08S (HAM) TUT 01 for Tuesday 8 January only Time: Tue 9:00 - 11:00 Location: I.G.02 COMP153-08S (HAM) LEC 01 Time: Mon 9:00 - 11:00 Location: K.G.07 COMP153-08S (HAM) TUT 01 Time: Tue 9:00 - 11:00; Location: K.G.06 COMP153-08S (HAM) LEC 02 Time: Wed 9:00 - 11:00 Location: K.G.07 COMP153-08S (HAM) TUT 02 Time: Thu 9:00 - 11:00 Location: K.G.06

3. Arithmetic Note: Lecture notes (and labs) are on the web at: www.cs.waikato.ac.nz/~geoff Operations –Add+ –Multiply* –Subtract- –Divide/ –Power^eg: 3^2 is 3 2

4. Order of operations Unless you use parentheses to say otherwise –Power is first –Then multiplication and division done in order from left to right –Then addition and subtraction in order from left to right

5. Examples 2 + 3 * 4 –Is 14, evaluated as 2 + (3 * 4) –If you want the addition done first, then you must write (2 + 3) * 4 30 / 2 * 3 –Is 45, done strictly from left to right –If you want this to mean 30 / 6 then you must write 30 / (2 * 3)

6. Types All values stored in a computer have a ‘Type’ – ie: the VB system has to know what kind of value it is dealing with – so it knows what operations can be performed on the value and how much storage to make available for it.

7. Examples of Types Integer –Holds whole numbers, roughly in the range +/- 2 billion –Eg: Button1.Width = 200 String –Hold sequences of characters – text –Eg: Button1.Text = “Press Me” –VB makes no attempt to ‘understand’ the content of a string

8. Another Type Single and Double –Hold fractional or very large numbers –Eg: 2.34 – 1.5E6 means 1.5 * 10 6 – 2.03E-5 means 2.03 * 10 -5

9. Operations on Types Integer values can have arithmetic operations applied to them So can single and double values Interestingly there is an operation that can be applied to String values The + operator joins two strings “ABC” + “DEF” gives “ABCDEF”

10. Type Conversion VB tries to be helpful and convert values from one type to another, in order to make sense of statements. TextBox1.Text = TextBox2.Text * 3.4 Doesn’t make sense – we cannot multiply a String by a number However VB will convert text to number, multiply and convert back

11. Care Automatic conversion doesn’t always do what we want We can explicitly do it ourselves –Val(…) converts String to number –Str(…) converts from number to String Eg: Val(Text1.Text) Eg: Str(100 * 34)

12. Copy program - before

13. Enter data into textbox and click Copy

14. Results in:

15. Exercise Try the same design but change the first box to Fahrenheit and the second to Celsius Change the Copy button to Convert C = (F – 32)/1.8

16. THE END of the lecture