If condition Then 'Your code here.. End If
Tip: In the VS studio IDE, if you type if until it's highlighted and then hit tab twice, the syntax will automatically be inserted.
Create a new VB Console Application and name it If Statements. Then copy the following:
Sub Main() Dim age As Integer Console.WriteLine("Please enter your age:") age = Console.ReadLine().ToString() If age = 15 Then Console.WriteLine("You are not old enough to drink") End If Console.ReadLine() End Sub
- First we created a variable called "age" with the data type integer.
- Next we printed to the console: "Please enter your age:"
- We then read the user's value.
- If you enter 15 you will see the message: "You are not old enough to drink".
- If you enter any other value the program will just terminate without any notification.
This is a simple If Statement. The problem with this If Statement is that if the condition evaluates to false (the age is not 15), the program will do nothing. In this case we can use an If Else Statement.
If condition Then code Else other code End If
Comment out the other If Statement (CTRL+K+C) and copy the following code:
Dim username As String Dim password As Integer username = Nothing password = Nothing Console.WriteLine("Enter Your UserName") username = Console.ReadLine() Console.WriteLine("Enter Your Password") password = Console.ReadLine() If username = "Asim" And password = 243 Then Console.WriteLine("Welcome Asim!") Else Console.WriteLine("Access is denied") End If Console.ReadLine()
This is similar to the above If Statement. You have two variables (string/integer) which we use to store the values the user enters when prompted. Then we compare those values to the values in our If Statement. So if username = "Asim" AND password = 243, then "Welcome Asim" is displayed; otherwise "Access Denied" is displayed. You are also using the logical operator And which will be explained later.
Nested If Else
You can also have a nested If Else Statement.
Dim message As String message = "Welcome " & username If username = "Asim" And password = 243 Then Console.WriteLine(message) Else If username = "Dave" And password = 12345 Then Console.WriteLine(message) Else If username = "Admin" And password = 2012 Then Console.WriteLine(message) Else Console.WriteLine("Oops could not find you!") End If End If End If
The process is the same as before, but we have more decisions. However, we have made a new string variable called "message"; this was made to avoid repeating the console message. The If Else Statement will see if the statements are true: if they are it will print out the correct message, and if they are false it will print the last message. If Else Statements can become quite long, so it is best to use a Select Case Statement which will be addressed in the next lesson.
If Else Statement Operators
There are various operators you can use with If Else Statements:
|<||Less than operator||if 19 < 20 Then|
|>||Greater than operator||if 20 > 19 Then|
|=||Equal to operator||if a = b Then|
|<>||Not equal to operator||if a <> b Then|
|<=||Less than or equal to operator||if 19 <= b Then|
|>=||Greater than or equal to operator||if 19 >= b Then|
Example of Less Than
If 15 < 20 Then Console.WriteLine("15 is greater than 20!") End If Console.ReadLine()
In this example the condition is simply asking "Is 15 less than 20?" Since this is true, the If Statement will execute.
Example of Not Equal To
Dim name As String name = "Adam" If name <> "Asim" Then Console.WriteLine("Name does not equal Asim, Name = " + name) End If Console.ReadLine()
In this example, the condition is saying "If name NOT EQUAL TO Asim." Since the variable "name" does not equal Asim, the condition is true and the If Statement will execute.
You can use the logical operators to extend the If Else Statements and use two conditions, for example if a = b And a > 19 Then
|And||And Operator - If both conditions are true, then the result is true|
|Or||Or Operator - If either of the conditions are true, the result will be true|
|Not||Not Operator - If the condition is false, then the result will be true, or vice versa.|
Example of Logical And Operator
Dim a As Integer Dim rnd As New Random a = rnd.Next(90, 160) If a > 100 And a < 150 Then Console.WriteLine("A is greater than 100, but less than 150, A = " + a.ToString()) End If Console.ReadLine()
The only difference with this example is we are using the random class to generate a random number between 90 - 160, which is assigned to the variable A. Then the If Statements condition is, "Is A greater than 100 AND less than 150?" If it is, it will continue to execute the If Statement; otherwise it will terminate.
In this tutorial you have learned about If Statements, If Else Statements and Nested If Else statements. In addition, you have learned how to use the Conditional and Logical operators to perform more actions based on various conditions.