Selection Flow Charts If statements Flow of Control

Selection Flow Charts If statements

Flow of Control The flow of control is a concept with which we’re already familiar. The concept of control relates to the machine level in which a single instruction controls the behaviour of the CPU. The flow of control describes how control passes from one instruction to the next.

Flow Charts A handy way to map the logic of a program is the Flow Charts use specific shapes to represent computer actions and join these together with arrows to show the flow of control. Each type of action is represented by a specific shape.

Flow Chart Symbols There is no single standard for flow chart shapes, but there is a widely used core set. • The start and end of a program are represented by lozenges, ovals or rounded rectangles. • The flow of control is represented by arrows. – An arrow coming from one symbol and ending at another symbol represents that control passes in the direction of the arrow.

Flow Chart Symbols • Processing steps are represented by rectangles. • Input/Output are represented by a variety of shapes, including parallelograms. – Some programmers use different symbols for input than for output. – Some even use different symbols for different types of input or output. (printer, screen, speaker, etc. )

Charting the Flow of Control Flow charts help visualise the flow of control. Declare vars for input and result get input The simplest form is sequence. produce result from input show result Note the use of alternate symbols for I/O.

Flow Chart Symbols Frequently, a program will need alternative logic paths, one for some data, and another for other data. In a flow chart a branch in the logic path is represented by a diamond.

Flow Chart Symbols • A condition (or decision) is represented by a diamond (rhombus). • These typically contain a Yes/No question or True/False test. • This symbol is unique in that it has two arrows coming from it: – one corresponding to Yes (or True) – and one corresponding to No (or False).

Branches in VB A branch in the logic of a VB program is created by the If statement. If <condition> Then … End If

If Then If condition Then ‘body End If True Condition False Process

If …Then…Else If condition Then ‘body False Else ‘body Process End If True Condition Process

Else. If If condition Then ‘body False Else Condition ‘body Process End If True Condition True Process

Else If If condition Then ‘body Else False If condition Then ‘body False Else Condition ‘body Process End If True Condition True Process

Nested Ifs If condition Then False If condition Then Condition ‘body False True False Else Condition ‘body End If Process Else If condition Then ‘body Else ‘body End If True Condition Process