Pseudocode An Introduction

Flowcharts were the first design tool to be widely used, but unfortunately they do not reflect some of the concepts of structured programming very well. Pseudocode, on the other hand, is a newer tool and has features that make it more reflective of the structured concepts. The drawback is that the narrative presentation is not as easy to understand and/or follow.

What is Pseudocode? Pseudocode is "halfway" between English and a programming language. It is a description of a process in detail, though not necessarily in full sentences. The key is to provide enough information so that anyone could follow the instructions (a child, an alien, or even a computer, if the instructions were translated into a language it understands). Recipes are one type of pseudocode, instructions for assembling things are another.

Rules for Pseudocode Write only one statement per line Capitalize initial keyword Indent to show hierarchy End multiline structures Keep statements language independent

One Statement Per Line Each statement in pseudocode should express just one action for the computer. If the task list is properly drawn, then in most cases each task will correspond to one line of pseudocode. Task List Read name, hours worked, rate of pay Perform calculations gross = hours worked * rate of pay Write name, hours worked, gross Pseudocode READ name, hoursWorked, payRate gross = hoursWorked * payRate WRITE name, hoursWorked, gross

Capitalize Initial Keyword In the example below note the words: READ and WRITE. These are just a few of the keywords to use, others include: READ, WRITE, IF, ELSE, ENDIF, WHILE, ENDWHILE Pseudocode READ name, hoursWorked, payRate gross = hoursWorked * payRate WRITE name, hoursWorked, gross

Example of Pseudocode for Washing the Dishes Close the sink drain hole squirt some dish liquid in the sink turn on hot water WHILE sink is not full     wait 2 seconds     splash water to create bubbles turn off water (sink is now full of hot, soapy water) put a dishrag in the sink WHILE there are dirty dishes     grab a dish     put dish in the sink     scrub dish with dishrag     IF dish is still dirty         THEN scrub dish with scouring pad     rinse dish     put dish in drainer open the sink drain hole put dishrag in laundry basket Drying the dishes is left as an exercise to the reader :) Even though this description is fairly complex, it still has some pieces missing. If there are nonstick dishes, we don't want to scratch them with the scouring pad. We don't want to wash greasy dishes first, since they will make the water dirty. There are no instructions for times when the dish drainer is full... The pseudocode you write should be detailed enough that it can be understood (by a child, alien, or computer) without being so detailed that it becomes difficult to follow.

Advantages & Disadvantages Flowchart Advantages: Standardized Visual Pseudocode Advantages Easily modified Implements structured concepts Done easily on Word Processor Flowchart Disadvantages: Hard to modify Structured design elements not implemented Special software required Pseudocode Disadvantages: Not visual No accepted standard, varies from company to company

References http://www.cs.indiana.edu/~rscherle/a106/lesson3.html http://faculty.ccri.edu/mkelly/COMI1150/Pseudocode%20Basics.ppt