Programming VB: ‘basics’

1. Programming VB: ‘basics’ Review & preview: Events, variables, statements, etc. Images, Control arrays, For/Next Assignment: read chapter 2 Paint Shop Pro Work on mix & match MAT 1420.20 Meyer Week 2

2. Variables • Variables ‘hold’ (are associated with) values • Values come in different datatypes • Integer (whole numbers, positive or negative) • Single (can have fractions) • String (sequence of characters) • Unlimited or fixed size • Boolean (logical value = True or False) MAT 1420.20 Meyer Week 2

3. Datatype conversion • Visual Basic will sometimes do this for you, but good practice is to do it explicitly • Strings in textboxes representing numbers must be converted to numbers in order to do arithmetic • Val(‘12’) => the number 12 • and numbers must be converted to strings to be displayed • Str(12) => the string ‘12’ • Format(12.3333, “currency”) => “$12.33” • Other possibilities for second parameter of Format. See HELP. MAT 1420.20 Meyer Week 2

4. Control objects • are objects placed on Forms • have properties (set or allowed to be default at design time and queried & changed during run time) • have pre-defined events. During design time, you write code = event procedure = event handler for certain events MAT 1420.20 Meyer Week 2

5. Labels & Textboxes • What are these and what is the difference? • How are they used in rock-paper-scissors? MAT 1420.20 Meyer Week 2

6. Command buttons • Has caption property • Has Click event • Note: certain other control objects can have Click event procedures. • Give examples from rock-paper-scissors MAT 1420.20 Meyer Week 2

7. Names • Computer Science is the field when people talk about the thing versus the name of the thing. • A textbox has • (name) as the first property • text property: the current contents of the textbox. • A label has • (name) as the first property • caption property: what you see in/on the label (changeable by code but not the player) • A command button has • (name) as the first property • caption property: what you see in/on the label (code can change this, but untypical) • An image control has • (name) as the first property • picture property: set by specifying an image file created outside VB. MAT 1420.20 Meyer Week 2

8. Control arrays • Sets of controls with the same name. Each one has its own index. • Indexing starts with zero. • Control array of textboxes, labels, image controls, etc. • Will be used in mix & match for the sets of choices for body parts, chance for the die faces, memory for the cards. • May be in different or the same location on the Form. MAT 1420.20 Meyer Week 2

9. Array variables • Internal array • You can specify the bounds: • Dim strDays (1 to 7) as String • 7 strings. The third one is strDays(3) • Dim sinCosts (0 to 5) as Single • 6 numbers. The third one is sinCosts(2) • Dim intTable (1 to 10, 1 to 3) as Integer • 10 times 3 = 30 integers. The one in the second row, third column is intTable(2,3) MAT 1420.20 Meyer Week 2

10. Statements are the action = what gets done • Give example of a statement from • The Hello, World programs • Rock paper scissors MAT 1420.20 Meyer Week 2

11. Events • Give examples of events from rock-paper-scissors MAT 1420.20 Meyer Week 2

12. List box control • Type of control • Used to allow player/user to specify items in a list • The items are set at run time, for example, as part of Form_Load • The critical property is listindex and the critical event is Click MAT 1420.20 Meyer Week 2

13. Image or picture control • Each are for holding/displaying pictures • Each have Picture property that you set at Design time by identifying an image file • (or at runtime by using LoadPicture command) • Visible property set to True or False controls if you can see the image • Top and Left properties govern position on the form MAT 1420.20 Meyer Week 2

14. For/Next statement • Also known as (aka) loops • Sets up repetition of a set of statements • Index variable, start, stop, and, optionally specify step if it is not 1 • For I = 1 to 10 … ‘ statements may or may not use I Next I MAT 1420.20 Meyer Week 2

15. Example sum = 0 For I = 2 to 10 step 2 sum = sum + I Next I What is sum? MAT 1420.20 Meyer Week 2

16. Example • Assume there is a control array of 5 label controls (lblSpots) all located at Left = 0, Top = 0 (where is that??) For I = 0 to 4 lblSpots.Left = I * 100 lblSpots.caption = str(I) Next I What would this do? MAT 1420.20 Meyer Week 2

17. Debugging • Programs do not always work the first time… • Debugging refers to the process of testing and refining programs. • Many errors are ‘caught’ when code is written or in the initial translation stages, but some errors are not. • Debugging tools include: Break, Breakpoints, Immediate window MAT 1420.20 Meyer Week 2

18. Mix & Match cartoons • Implements the book in which you can choose a hat, head, body and shoes/feet • Requires sets of image files that are the body parts. • List box for each body part • Control array of images for each body part • Listbox items will correspond to elements of the appropriate body part control array MAT 1420.20 Meyer Week 2

19. Parallel structures • Common programming technique is to have array or list structures and have correspondence between items. • List box for hats: • “floppy” • “tall” • Control array: imgHats • imgHats(0) has picture property floppy.bmp • imgHats(1) has picture property tall.bmp MAT 1420.20 Meyer Week 2

20. Assignment • Read chapter 2 • Next class: • Paint Shop Pro lesson • Time to create your own images (Photo Shop okay & ‘acquiring’ images okay) • Work on Mix & match cartoons in lab MAT 1420.20 Meyer Week 2