Pseudocode: A Structured Programming Tool, Study notes of Design

Download Pseudocode: A Structured Programming Tool and more Study notes Design in PDF only on Docsity! Pseudocode: An Introduction Flowcharts were the first design tool to be widely used, but unfortunately they do not very well reflect some of the concepts of structured programming. Pseudocode, on the other hand, is a newer tool and has features that make it more reflective of the structured concepts. Unfortunately, the narrative presentation is not as easy to understand and follow. RULES FOR PSEUDOCODE 1. Write only one stmt per line Each stmt in your 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. EX: TASK LIST: Read name, hourly rate, hours worked, deduction rate Perform calculations gross = hourlyRate * hoursWorked deduction = grossPay * deductionRate net pay = grossPay – deduction Write name, gross, deduction, net pay PSEUDOCODE: READ name, hourlyRate, hoursWorked, deductionRate grossPay = hourlyRate * hoursWorked deduction = grossPay * deductionRate netPay = grossPay – deduction WRITE name, grossPay, deduction, netPay 2. Capitalize initial keyword In the example above, READ and WRITE are in caps. There are just a few keywords we will use: READ, WRITE, IF, ELSE, ENDIF, WHILE, ENDWHILE, REPEAT, UNTIL 3. Indent to show hierarchy We will use a particular indentation pattern in each of the design structures: SEQUENCE: keep statements that are “stacked” in sequence all starting in the same column. SELECTION: indent the statements that fall inside the selection structure, but not the keywords that form the selection LOOPING: indent the statements that fall inside the loop, but not the keywords that form the loop EX: In the example above, employees whose grossPay is less than 100 do not have any deduction. TASK LIST: Read name, hourly rate, hours worked, deduction rate Compute gross, deduction, net pay Is gross >= 100? YES: calculate deduction NO: no deduction Write name, gross, deduction, net pay PSEUDOCODE: READ name, hourlyRate, hoursWorked grossPay = hourlyRate * hoursWorked IF grossPay >= 100 deduction = grossPay * deductionRate ELSE deduction = 0 ENDIF netPay = grossPay – deduction WRITE name, grossPay, deduction, netPay 4. End multiline structures See how the IF/ELSE/ENDIF is constructed above. The ENDIF (or END whatever) always is in line with the IF (or whatever starts the structure). 5. Keep stmts language independent Resist the urge to write in whatever language you are most comfortable with. In the long run, you will save time! There may be special features available in the language you plan to eventually write the program in; if you are SURE it will be written in that language, then you can use the features. If not, then avoid using the special features. LOOPING STRUCTURES One of the most confusing things for students first seeing a flowchart is telling the loops apart from the selections. This is because both use the diamond shape as their control symbol. In pseudocode this confusion is eliminated. To mark our loops we will use these pairs: WHILE / ENDWHILE REPEAT / UNTIL The loop shown here (from the last chapter) will have the following pseudocode: count = 0 WHILE count < 10 ADD 1 to count WRITE count ENDWHILE WRITE “The end” Notice that the connector and test at the top of the loop in the flowchart become the WHILE stmt in pseudocode. The end of the loop is marked by ENDWHILE. What statement do we execute when the loop is over? The one that follows the ENDWHILE. Sometimes it is desirable to put the steps that are inside the loop into a separate module. Then the pseudocode might be this: Mainline We often use this name for the first module. count = 0 Initialization comes first WHILE count < 10 DO Process The processing loop uses this module ENDWHILE WRITE “The end” Termination does clean-up Process Go thru these steps and then return to the ADD 1 to count module that sent you here (Mainline) WRITE count START Count = 0 Count < 10 Add 1 to count STOP Write count no yes Write “The end” This time we will see how to write pseudocode for an UNTIL loop: count = 0 REPEAT ADD 1 to count WRITE count UNTIL count >= 10 WRITE “The end” Notice how the connector at the top of the loop corresponds to the REPEAT keyword, while the test at the bottom corresponds the the UNTIL stmt. When the loop is over, control goes to the stmt following the UNTIL. START Count = 0 Add 1 to count Write count Count >= 10 STOP no yes Write “The end” ADVANTAGES AND DISADVANTAGES Pseudocode Disadvantages  It’s not visual  There is no accepted standard, so it varies widely from company to company Pseudocode Advantages  Can be done easily on a word processor  Easily modified  Implements structured concepts well Flowchart Disadvantages  Hard to modify  Need special software (not so much now!)  Structured design elements not all implemented Flowchart Advantages  Standardized: all pretty much agree on the symbols and their meaning  Visual (but this does bring some limitations) HOW WE STORE AND ACCESS DATA What happens when we execute READ stmt? READ name, hoursWorked, hourlyRate, deductionRate The computer stores all program data into memory locations. It knows these location by their addresses. It is perfectly able to understand code like: READ 19087, 80976, 10943, 80764 but we would have a hard time with it. So we name our storage locations using words that are descriptive to us. Every language has its own (different) set of rules about how these names are formed. We will use a simple style:  variable names will start with a lowercase letter  they will have no spaces in them  additional words in them will start with a capital  names must be unique within the program  consistent use of names The READ statement tells the computer to get a value from the input device (keyboard, file, …) and store it in the names memory location. When we need to compute a value in a program (like grossPay) we will use what is called an assignment stmt. variable = expression Be careful to understand the difference between these two stmts: num1 = num2 num2 = num1