Convoluted conditional expressions like the one shown in Listing 2.1, scattered throughout the code, are unnecessarily complex and expensive to evaluate at runtime. They are also notoriously difficult to get right, even by experienced programmers, as the bugs still lurking in the Visual Basic calculator attest. This approach is insidious because it appears to work fine initially, but doesn't scale up as the problem grows in complexity. Apparently, the calculator application (overall only seven event handlers and some 140 lines of Visual Basic code including comments) is just complex enough to be difficult to get right with this approach.