Programming Concepts and Skills. ASCII and other codes

Transcription

1 Programming Concepts and Skills ASCII and other codes

2 Data of different types We saw briefly in Unit 1, binary code. A set of instructions written in 0 s and 1 s, but what if we want to deal with more information than either true or false? There are several other types used by computers. We will take a look at a few of those.

3 Octal The octal numeral system, or oct for short, is the base 8 number system, and uses the digits 0 to 7. Octal numerals can be made from binary numerals by grouping consecutive binary digits into groups of three (starting from the right). For example, the binary representation for decimal 74 is , which can be grouped into (00) so the octal representation is 112.

4 Hexadecimal In mathematics and computer science, hexadecimal (also base 16, or hex) is a numeral system with a base of 16. It uses sixteen distinct symbols, most often the symbols 0 9 to represent values zero to nine, and A, B, C, D, E, F (or alternatively a f) to represent values ten to fifteen. For example, the hexadecimal number 2AF3 is equal, in decimal, to ( ) + ( ) + ( ) + ( ), or

5 RGB and Hexadecimal In the RGB Color System used in computers there are 256 possible levels of brightness for each component in an RGB (Red, Green, Blue) color. So the red component, blue component and the green component can each be represented by a byte, or two hexadecimal digits. An entire RGB color can therefore be represented by six hexadecimal digits. This is most often how they are referenced in software like Photoshop, Fireworks and even VB.

6 ASCII The American Standard Code for Information Interchange is a character encoding scheme originally based on the English alphabet that encodes 128 specified characters the numbers 0 9, the letters a z and A Z, some basic punctuation symbols, some control codes that originated with Teletype machines, and a blank space into the 7 bit binary integers.

7 ASCII codes represent text in computers, communications equipment, and other devices that use text. Most modern character encoding schemes are based on ASCII, though they support many additional characters.

8 For a list of the ASCII Printable Characters, click here.

9 Unicode Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems. Developed in conjunction with the Universal Character Set standard and published in book form as The Unicode Standard, the latest version of Unicode contains a repertoire of more than 110,000 characters covering 100 scripts.

10 For a list of Unicode Characters, click here.

11 Repetition Control Structures Visual Basic loop structures allow you to run one or more lines of code repetitively. You can repeat the statements in a loop structure until a condition is True, until a condition is False, a specified number of times, or once for each element in a collection.

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13 While Loops The While...End While construction runs a set of statements as long as the condition specified in the While statement is True. Dim index As Integer = 0 While index <= 10 Debug.Write(index.ToString & " ") index += 1 End While Debug.WriteLine("") ' Output:

14 Do Loop The Do...Loop construction allows you to test a condition at either the beginning or the end of a loop structure. You can also specify whether to repeat the loop while the condition remains True or until it becomes True.

15 Examples Dim index As Integer = 0 Do Debug.Write(index.ToString & " ") index += 1 Loop Until index > 10 Debug.WriteLine("") ' Output: Example 2: Dim index As Integer = 0 Do While index <= 10 Debug.Write(index.ToString & " ") index += 1 Loop Debug.WriteLine("") ' Output:

16 For Next Loop The For...Next construction performs the loop a set number of times. It uses a loop control variable, also called a counter, to keep track of the repetitions. You specify the starting and ending values for this counter, and you can optionally specify the amount by which it increases from one repetition to the next. Most common type of Loop used.

17 Example 1 For index As Integer = 1 To 5 Debug.Write(index.ToString & " ") Next Debug.WriteLine("") ' Output:

18 Example 2 For number As Double = 2 To 0 Step 0.25 Debug.Write(number.ToString & " ") Next Debug.WriteLine("") ' Output:

19 For Each Next Loop The For Each...Next construction runs a set of statements once for each element in a collection. You specify the loop control variable, but you do not have to determine starting or ending values for it.

20 Example ' Create a list of strings by using a ' collection initializer. Dim lst As New List(Of String) _ From {"abc", "def", "ghi"} ' Iterate through the list. For Each item As String In lst Debug.Write(item & " ") Next Debug.WriteLine("") 'Output: abc def ghi

21 Nested Loops It will happen that you will have to code a loop within a loop(s). Remember to indent your code so you can easily see the conditions of each loop. You should always indent when you have new conditional statements as well.

22 Example For indexa = 1 To 3 ' Create a new StringBuilder, which is used ' to efficiently build strings. Dim sb As New System.Text.StringBuilder() ' Append to the StringBuilder every third number ' from 20 to 1 descending. For indexb = 20 To 1 Step 3 sb.append(indexb.tostring) sb.append(" ") Next indexb ' Display the line. Debug.WriteLine(sb.ToString) Next indexa ' Output: ' ' '

23 Now try these loops So in today s activity, you will try the first three types of loops to see the difference between them. First, you will get a number value from the user in a text box. You will then display the value after your loop completes, using the value given by the user, by writing to the label object for the appropriate loop.

24 Your form should look like this

25 Once complete, copy your working project folder to the DropOff folder on the X:drive. This is activity is 3_6_Loops.