Practical Programming

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 32

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 * 106 • 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