Cross Ref > Operators

VB.Net uses = for it's assignment operator.

Syntax Example:   Dim Age As Integer Dim FullName As String FullName = "Randy Spitz" Age = 38

ASP Classic uses = for it's assignment operator.

FullName = "Randy Spitz"
Age = 38

Save as VB Classic. Common comparison operators:

Syntax Example:   //Does VB.Net evaluate the math correctly? No! If 0.1 + 0.1 + 0.1 = 0.3 Then MessageBox.Show("correct") Else MessageBox.Show("not correct") End If

Save as VB Classic. Common comparison operators:

//Does ASP evaluate the math correctly? No!

If .1 + .1 + .1 = .3 Then
  Response.Write "correct"
Else
  Response.Write "not correct"
End If

 ASP Classic Comparison Operators (=, <>)

In .Net, a string can be null or empty. The .Net framework offers a static method in the string class: String.IsNullOrEmpty to check if a string is null or empty.

Syntax Example:   Dim s As String 's = "" 'Uncomment to test 2nd case. If String.IsNullOrEmpty(s) Then   MessageBox.Show("hello") End If

In ASP Classic, you have to add an empty string to the value being compared in order to get consistent results. For example, add &"" to your string varilable or it's code equivalent &vbNullString. Then compare to an empty string or verify it's length to 0 with Len.

If s&"" = "" Then
  Response.Write("<br>Quotes with &'' say null is empty")
End If

 
If Len(s&"") = 0 Then
  Response.Write("<br>Len with &'' says null is empty")
End If

If Len(s&vbNullString) = 0 Then
  Response.Write("<br>Using vbNullString also works!")
End If

 ASP Classic Empty String Check (Len(s&vbNullString))  

VB.Net logical operators:

Syntax Example:   'Given expressions a, b, c, and d: If Not (a and b) and (c or d) Then   'Do something. End If

Same as VB. ASP Classic logical operators:

ASP Classic never short circuits. Given the expression this or that as well as this and that, if this evaluates to false, then that is still executed.

'Given expressions a, b, c, and d:

If Not (a and b) and (c or d) Then

  'Do something.

End If

 ASP Classic Logical Operators (and, or, not)  

To concatenate two strings, use either the + or & operators. The & operator implicitly converts numbers. If you use the + operator to concatenate a string and a number, you have to cast the number as a string with CStr.

Alternatively, you can use the System.Text.StringBuilder class which frequently but not always provides faster code.

Dim FullName

Dim Age

//You can use + for strings.

FullName = "Prestwood"
Console.WriteLine("Hello " + FullName)

//For implicit casting, use &

Age = 35

Console.WriteLine(FullName & " is " & Age & " years old.")

'Implicit casting of numbers.

'

'This works:
MessageBox.Show(3.3)

'This fails:

'MessageBox.Show("" + 3.3)

'This works:
MessageBox.Show("" + CStr(3.3))

'Implicit casting &. This also works:

MessageBox.Show("" & 3.3)

Although you can use either a & or a + to concatenate values, my preference is to use a + because more languages use it. However, if you use & then some type conversions are done for you. If you use + you will sometimes have to cast a value to concatenate it. For example, you will have to use CStr to cast a number to a string if you use the + operator as a concatenation operator.

Dim FirstName
Dim LastName

FirstName  = "Mike"
LastName  = "Prestwood"

Response.Write "Full name: " & FirstName & " " + LastName

Response.Write "2+2=" + CStr(2+2)

An operation with only one operand (a single input). A unary operator method can return any type but takes only one parameter, which must be the type of the containing class. In addition to the obvious +, -, and Not operators, VB.Net also offers:

 VB.Net Unary Operators

An operation with only one operand (a single input) such as +, -, and Not.

 ASP Classic Unary Operators