Formula fields within Crystal Reports allow you to inject code blocks within a report when simple Select SQL statements can't do the trick.  You can declare variables, create if-then blocks, create arrays, execute loops, or call built in functions within Crystal Reports.  This article will create a Crystal Report in an ASP.NET web site project and demonstrate how to create a formula field, manipulate a date in the formula as well as elaborate on how to declare a variable and assign it a value, and also use if-then logic to create summary fields by quarter on the report.

Before you begin you will need to have installed Visual Studio 2008 with Crystal Reports for .NET.  The samples are written in Visual Studio 2008 but they will work with Visual Studio 2005 also. I created a simple database with one table to use for the sample report. The code for the sample report created in this article can be found here.