Flowcharts

Overview

A flowchart is a type of diagram that represents an algorithm, workflow or process. The flowchart shows the steps as boxes of various kinds, and their order by connecting the boxes with arrows. This diagrammatic representation illustrates a solution model to a given problem. Flowcharts are used in analyzing, designing, documenting or managing a process or program in various fields.^[1]

Discussion

Common flowcharting symbols and examples follow. When first reading this section, focus on the simple symbols and examples. Return to this section in later chapters to review the advanced symbols and examples.

Simple Flowcharting Symbols

Terminal

The rounded rectangles, or terminal points, indicate the flowchart’s starting and ending points.

Flow Lines

Note: The default flow is left to right and top to bottom (the same way you read English). To save time arrowheads are often only drawn when the flow lines go contrary the normal.

Input/Output

The parallelograms designate input or output operations.

Process

The rectangle depicts a process such as a mathematical computation, or a variable assignment.

Decision

The diamond is used to represent the true/false statement being tested in a decision symbol.

Advanced Flowcharting Symbols

Module Call

A program module is represented in a flowchart by rectangle with some lines to distinguish it from process symbol. Often programmers will make a distinction between program control and specific task modules as shown below.

Local module: usually a program control function.

Library module: usually a specific task function.

Connectors

Sometimes a flowchart is broken into two or more smaller flowcharts. This is usually done when a flowchart does not fit on a single page, or must be divided into sections. A connector symbol, which is a small circle with a letter or number inside it, allows you to connect two flowcharts on the same page. A connector symbol that looks like a pocket on a shirt, allows you to connect to a flowchart on a different page.

On-Page Connector

Off-Page Connector

Simple Examples

We will demonstrate various flowcharting items by showing the flowchart for some pseudocode.

Functions

pseudocode: Function with no parameter passing

Function clear monitor Pass In: nothing Direct the operating system to clear the monitor Pass Out: nothing End function

pseudocode: Function main calling the clear monitor function

Function main Pass In: nothing Doing some lines of code Call: clear monitor Doing some lines of code Pass Out: value zero to the operating system End function

Sequence Control Structures

The next item is pseudocode for a simple temperature conversion program. This demonstrates the use of both the on-page and off-page connectors. It also illustrates the sequence control structure where nothing unusual happens. Just do one instruction after another in the sequence listed.

pseudocode: Sequence control structure

Filename: Solution_Lab_04_Pseudocode.txt Purpose: Convert Temperature from Fahrenheit to Celsius Author: Ken Busbee; © 2008 Kenneth Leroy Busbee Date: Dec 24, 2008 Pseudocode = IPO Outline input display a message asking user for the temperature in Fahrenheit get the temperature from the keyboard processing calculate the Celsius by subtracting 32 from the Fahrenheit temperature then multiply the result by 5 then divide the result by 9. Round up or down to the whole number. HINT: Use 32.0 when subtracting to ensure floating-point accuracy. output display the celsius with an appropriate message pause so the user can see the answer 

Advanced Examples

Selection Control Structures

pseudocode: If then Else

If age > 17 Display a message indicating you can vote. Else Display a message indicating you can't vote. Endif

pseudocode: Case

Case of age 0 to 17 Display "You can't vote." 18 to 64 Display "You are in your working years." 65 + Display "You should be retired." End case

Iteration (Repetition) Control Structures

pseudocode: While

count assigned zero While count < 5 Display "I love computers!" Increment count End while

pseudocode: For

For x starts at 0, x < 5, increment x Display "Are we having fun?" End for

The for loop does not have a standard flowcharting method and you will find it done in different ways. The for loop as a counting loop can be flowcharted similar to the while loop as a counting loop.

pseudocode: Do While

count assigned five Do Display "Blast off is soon!" Decrement count While count > zero

pseudocode: Repeat Until

count assigned five Repeat Display "Blast off is soon!" Decrement count Until count < one

Key Terms

decision symbol

A diamond used in flowcharting for asking a question and making a decision.

flow lines

Lines (sometimes with arrows) that connect the various flowcharting symbols.

flowcharting

A programming design tool that uses graphical elements to visually depict the flow of logic within a function.

input/output symbol

A parallelogram used in flowcharting for input/output interactions.

process symbol

A rectangle used in flowcharting for normal processes such as assignment.

References

• cnx.org: Programming Fundamentals – A Modular Structured Approach using C++