Читать книгу Excel 2019 Power Programming with VBA - Michael Alexander, Dick Kusleika - Страница 195

Hang around with programmers, and sooner or later you'll hear the term structured programming. You'll also discover that structured programs are considered superior to unstructured programs.

So, what is structured programming, and can you do it with VBA?

The basic premise of structured programming is that a routine or code segment should have only one entry point and one exit point. In other words, a body of code should be a stand-alone unit, and program control should not jump into or exit from the middle of this unit. As a result, structured programming rules out the GoTo statement. When you write structured code, your program progresses in an orderly manner and is easy to follow—as opposed to spaghetti code, in which a program jumps around.

A structured program is easier to read and understand than an unstructured one. More important, it's also easier to modify.

VBA is a structured language. It offers standard structured constructs, such as If-Then-Else and Select Case and the For-Next, Do Until, and Do While loops. Furthermore, VBA fully supports modular code construction.

If you're new to programming, form good structured programming habits early.

The following is an example of a For-Next loop that doesn't use the optional Step value or the optional Exit For statement. This routine executes the Sum = Sum + Sqr(Count) statement 100 times and displays the result, that is, the sum of the square roots of the first 100 integers.

Sub SumSquareRoots() Dim Sum As Double Dim Count As Integer Sum = 0 For Count = 1 To 100 Sum = Sum + Sqr(Count) Next Count MsgBox Sum End Sub

In this example, Count (the loop counter variable) starts out as 1 and increases by 1 each time the loop repeats. The Sum variable simply accumulates the square roots of each value of Count.