If (Condition) Then. Statements executed if condition is true Else If Statements executed else if condition is false Else

Transcription

1 CBVP2103

2 If (Condition) Then Statements executed if condition is true Else If Statements executed else if condition is false Else Statements executed if condition is false End If

3 Every If statement must contain a then and an end if Example: If Num1 < 2 Then MessageBox.show( The value is less than 2 ) End If If Num1 <> 4 then MessageBox.Show( The value is not 4 ) End If The relational operators that can be used in VB are > < = >= <= <> (Not equal to)

4 Dim dtcurrent As System.DateTime Dim ihour As Integer dtcurrent = dtcurrent.now() ihour = dtcurrent.hour If (ihour < 12) Then MessageBox.Show ("Good Morning!") Else If (ihour >= 12) And (ihour < 18) Then MessageBox.Show ("Good Afternoon!") Else MessageBox.Show ("Good Evening!") End If

5 Dim intscore As Integer intscore = 23 'Single line If statement. If intscore < 50 Then MessageBox.Show("Failed.") : MessageBox.Show("Please try again.") 'Multi-line If statement. If intscore < 50 Then MessageBox.Show("Failed.") MessageBox.Show("Please try again.") End If

6 The select case statement is a lot like the switch statement in Java It can use ANY data type in VB Example Select Case Num1 Case 1 DoSomeThing() Case 2 Do SomethingElse() End Select Yes you can use strings as well

7 Select Case var Case 1 stmt1 // executed if var = 1 Case 2 stmt2 // executed if var = 2 Case Else stmt3 // executed if var is other than 1 and 2 End Select

8 For <<var>> = start To end Step <<val>> Statements Next Example: For I = 1 To 10 Step 2 Console.WriteLine(I) Next Here the values printed will be 1,3,5,7,9

9 This statement allows to iterate over the elements in arrays and collections. Dim a As String() = {"Chirag", "Bhargav", "Tejas"} Dim b As String For Each b In a MessageBox.Show(b) Next b

10 Dim product As Integer = 2 While product <= 1000 Console.Write("{0} ", product) product = product * 2 End While Console.WriteLine("Smallest power of 2 " & _ "greater than 1000 is {0}", product)

11 Do while loops evaluate the expression first then executes the Loop Body Act much in the same as All While loops in languages like C++ and Java Example: Do While Num1 < 10 Num1 += 1 Loop

12 1. Do While(a<>0) Console.Writeline(a) a = a 1 Loop 2. Do Console.Writeline(a) a = a 1 Loop While(a<>0) Both will print the value of a as long as a is not equal to 0. If a = 0, then the loop stops

13 1. Do Until(a=0) Console.Writeline(a) a = a 1 Loop 2. Do Console.Writeline(a) a = a 1 Loop Until(a=0) Both will print the value of a until a becomes 0. If a = 0, then the loop stops.

14 While Loop Execution stops if condition fails Execution continues if condition is true Until Loop Execution stops if condition becomes true Execution continues if condition is false

15 An array variable is a collection of simple variables of the same type to which Visual Basic can efficiently assign a list of values. Dim ArrayName(Dim1Index, Dim2Index,...) As DataType Dim arrayname(n) As DataType Example: Dim Employees(9) As String

16 To refer to an element of an array, you use the array name and an array index enclosed in parentheses. Employees(5) = "Leslie"

17 Private Sub ShowSquares() Dim squares(10) As Integer For i As Integer = 0 To 10 squares(i) = i * i Next i Dim txt As String = For i As Integer = 0 To 10 txt &= squares(i).tostring & vbcrlf Next i MessageBox.Show(txt) End Sub

18 The Array class provides several other useful shared methods that were not available in Visual Basic 6 and earlier versions. For example, the IndexOf and LastIndexOf methods return the position of a particular item in an Array object s items. The Array.Reverse method reverses the order of the items in an array.

19 The Array.Sort method sorts the items in the array. To sort the items, this method must compare them to each other. That means the items must be things that can be reasonably compared (such as integers, strings, or dates). Dim people(4) As Person Array.Sort(people)

20 String is a collection of characters VB.NET stores string data in instances of String class String class is a member of System namespace Code to declare a string: Dim s1 As String = "Hello Again"

21 Copy method returns a second String that is a copy of the String sent as an argument ' create a copy of s1 Dim s2 As String = String.Copy(s1) MessageBox.Show("s2, a copy of s1, contains " & _ s2)

22 Length method returns the size of the string ' Find the lengthe of s2 Dim s2 As String = some string MessageBox.Show("Length of string2: " & _ s2.length)

23 Chars method returns the character at a specified index MessageBox.Show("char at index 6 of s1 is " & s1.chars(6))

24 There are two options to see whether two string values are equal Equal sign (=) If s1 = s2 Then MessageBox.Show("s1 = s2") Equals method MessageBox.Show("s1.Equals(s2) returns " & s1.equals(s2))

25 SubString method: Extracts one or more characters from a String instance Returns a new String instance containing extracted characters MessageBox.Show("s1.Substring(0, 5) returns " & _ s1.substring(0, 5))

26 Replace method replaces one or more characters in a string with one or more other characters MessageBox.Show("s1.Replace(Hello, Hi) " & _ "returns " & s1.replace("hello", "Hi")) MessageBox.Show("After Replace s1 contains " & _ s1)

27 Insert method inserts one or more characters into an existing string beginning at a specified index MessageBox.Show("s1.Insert(6, There ) returns " & _ s1.insert(6, "There "))

28 StartsWith method Compares the string argument with beginning characters of the String instance. Returns True or False depending on whether there is a match MessageBox.Show("s1.StartsWith(Hi) returns " & _ s1.startswith("hi"))

29 EndsWith method compares the ending characters with the argument MessageBox.Show("s1.EndsWith(Again) returns " & _ s1.endswith("again")) Use ToUpper method to change the case of a string value to uppercase Use ToLower method to change the case of a string value to lowercase

30 IndexOf method Searches a String instance for a specific value Returns index of the beginning of the value Returns 1 if no matching value was found MessageBox.Show("s1.indexof(Again) returns " & _ s1.indexof("again"))

31 Use ToString method to convert numeric values to a string ' convert an integer to String Dim i As Integer = 5 MessageBox.Show("value of Convert.ToString(i) is " & _ Convert.ToString(i)) Use methods in Convert class to convert String values containing numeric data to primitive data types

32 Code to create a String array: ' declare a String array with 4 elements Dim stringarray(3) As String Elements of the stringarray are reference variables of data type String

33 Code to create four String instances and populate the array elements stringarray(0) = "Hello" stringarray(1) = "World" stringarray(2) = "Wide" stringarray(3) = "Web" A specific element can be accessed using the index of that element. String methods can be invoked for String instances referenced by array elements.