SSRS Expressions

Expressions are used throughout the report definition to specify or calculate values for parameters, queries, filters, report item properties, group and sort definitions, text box properties, bookmarks, document maps, dynamic page header and footer content, images, and dynamic data source definitions.
Here are some of the reporting services expressions:
1.To get Today’s date 
=Today
2.The following code will get Today's date -3 days
=DateAdd("d", -3, Today)
3.Get the Name of the day - like sunday
=WeekdayName(DatePart("w", Today))
4.SWITCH statement - An alternative to IIF/CASE 
=SWITCH(WeekdayName(Fields!Date.Value) = "Monday","Blue",
WeekdayName(Fields!Date.Value) = "Tuesday","Green",
WeekdayName(Fields!Date.Value) = "Wednesday","Red")

5.Format Numbers as Currency 
=FormatCurrency(1000)
6. Convert integer values to string
= CStr(123123)
7.The Iif function returns one of two values depending on whether the expression is true or not.

=IIF(Fields!LineTotal.Value > 100, True, False) 

8.Use multiple IIF functions (also known as "nested IIFs") to return one of three values depending on the value of PctComplete. The following expression can be placed in the fill color of a text box to change the background color depending on the value in the text box.

=IIF(Fields!PctComplete.Value >= 10, "Green", IIF(Fields!PctComplete.Value >= 1, "Blue", "Red"))

9.Test the value of the ImportantDate field and return "Red" if it is more than a week old, and "Blue" otherwise. This expression can be used to control the Color property of a text box in a report item:

=IIF(DateDiff("d",Fields!ImportantDate.Value,Now())>7,"Red","Blue")

10.Test the value of the Department field and return either a subreport name or a null (Nothing in Visual Basic). This expression can be used for conditional drillthrough subreports.

=IIF(Fields!Department.Value = "Development", "EmployeeReport", Nothing)

11.The Sum function can total the values in a group or
data region. This function can be useful in the header or footer of a group.

=Sum(Fields!LineTotal.Value, "Order") 

12.You can also use the Sum function for conditional aggregate calculations.

=Sum(IIF(Fields!State.Value = "Finished", 1, 0)) 

13.The RowNumber function, when used in a text box within a data region, displays the row number for each instance of the text box in which the expression appears. This function can be useful to number rows in a table. It can also be useful for more complex tasks, such as providing page breaks based on number of rows
The scope you specify for RowNumber controls when renumbering begins. The Nothing keyword indicates that the function will start counting at the first row in the outermost data region. To start counting within nested data regions, use the name of the data region. To start counting within a group, use the name of the group.

=RowNumber(Nothing)

14.Color alternate rows in table with a different color - This is very useful when there are a lot of rows with similar data and its hard to differentiate the rows. You have to set the table background color property with the following code.

=iif(RowNumber(Nothing) Mod 2, "WhiteSmoke", "White")
15. Dynamic DataSource - If you have a requirement for a report to be run against multiple database server you can change the datasource connection string property to be dynamic. You can write your own expression in the connection string option in the data source properties. The following will create a dynamic connection to the server depending on the report parameter (ServerName) selected. Note: You have to make sure that the login has permission on all the servers you would like to connect to.

="Data Source=" & Parameters!ServerName.Value & ";Initial Catalog=WSS_Content"
16.Combine more than one field by using concatenation operators and Visual Basic constants. The following expression returns two fields, each on a separate line in the same text box:

=Fields!FirstName.Value & vbCrLf & Fields!LastName.Value

17.Format dates and numbers in a string with the Format function.

=Format(Parameters!StartDate.Value, "M/D") & " through " & Format(Parameters!EndDate.Value, "M/D")

18.The Right, Len, and InStr functions are useful for returning a substring, for example, trimming DOMAIN\username to just the user name. The following expression returns the part of the string to the right of a backslash (\) character from a parameter named User:

=Right(Parameters!User.Value, Len(Parameters!User.Value) - InStr(Parameters!User.Value, "\"))

19.The following expression results in the same value as the previous one, using members of the .NET Framework System.String class instead of Visual Basic functions:
=User!UserID.Substring(User!UserID.IndexOf("\")+1, User!UserID.Length-User!UserID.IndexOf("\")-1)

20.Join - Display the selected values from a multivalue  parameter
=Join(Parameters!MyParameter.Value,",")
21.The Regex functions from the .NET Framework System.Text.RegularExpressions are useful for changing the format of existing strings, for example, formatting a telephone number. The following expression uses the Replace function to change the format of a ten-digit telephone number in a field from "nnn-nnn-nnnn" to "(nnn) nnn-nnnn": 

=System.Text.RegularExpressions.Regex.Replace(Fields!Phone.Value, "(\d{3})[ -.]*(\d{3})[ -.]*(\d{4})", "($1) $2-$3")