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Programming algorithms and flowchart.ppt
The document provides an overview of programming concepts, algorithms, and flowcharts, explaining how programming involves writing instructions in a computer-understandable format using programming languages. It discusses the steps in problem-solving, the role of pseudocode, and different control structures like sequence, decision, and repetition within programming. Additionally, it illustrates how to represent algorithms and their corresponding flowcharts through various examples, emphasizing the importance of matching the flowchart with the algorithm's logic.
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Programming algorithms and flowchart.ppt
- 1.
- 2.What is Programming?Series of instructions to a computer toaccomplish a task Instructions must be written in a way thecomputer can understand Programming languages are used to writeprograms
- 3.ALGORITHMS AND FLOWCHARTSA typical programming task can be divided intotwo phases: Problem solving phase produce an ordered sequence of steps that describesolution of problem this sequence of steps is called an algorithm Implementation phase implement the program in some programminglanguage
- 4.Devise an algorithmfor cooking a sausage on a barbecue
- 5.Steps in ProblemSolving First produce a general algorithm. Refine the algorithm successively to get step bystep detailed algorithm that is very close to acomputer language. Pseudocode is an artificial and informallanguage that helps programmers developalgorithms. Pseudocode is very similar toeveryday English.
- 6.Pseudocode & AlgorithmExample 1: Write an algorithm todetermine a student’s final grade andindicate whether it is passing or failing.The final grade is calculated as theaverage of four marks. Start with a general algorithm.
- 7.General AlgorithmPseudocode: Inputa set of 4 marks Calculate their average by summing and dividingby 4 if average is below 50Print “FAIL”elsePrint “PASS”
- 8.Detailed AlgorithmStep 1:Input M1,M2,M3,M4Step 2: GRADE (M1+M2+M3+M4)/4Step 3: if (GRADE < 50) thenPrint “FAIL”elsePrint “PASS”endif
- 9.Task: add twonumbers Pseudocode:StartGet two numbersAdd themPrint the answerEnd
- 10.Next Step -The Flowchart A graphical representation of the sequence ofoperations in an information system or program.Information system flowcharts show how data flows fromsource documents through the computer to finaldistribution to users. Program flowcharts show thesequence of instructions in a single program orsubroutine. Different symbols are used to draw eachtype of flowchart. The sequence of the flowchart and the algorithm MUSTmatch.
- 11.The FlowchartA Flowchartshowslogic of an algorithmemphasizes individual steps and theirinterconnectionse.g. control flow from one action to the next
- 12.Flowchart SymbolsBasicOvalParallelogramRectangleDiamondHybridName SymbolUse in FlowchartDenotes the beginning or end of the programDenotes an input operationDenotes an output operationDenotes a decision (or branch) to be made.The program should continue along one oftwo routes. (e.g. IF/THEN/ELSE)Denotes a process to be carried oute.g. addition, subtraction, division etc.Flow line Denotes the direction of logic flow in the programModuleDenotes a self-contained section of theprogram
- 13.ExamplePRINT“PASS”Step 1: InputM1,M2,M3,M4Step 2: GRADE (M1+M2+M3+M4)/4Step 3: if (GRADE <50) thenPrint “FAIL”elsePrint “PASS”endifSTARTInputM1,M2,M3,M4GRADE(M1+M2+M3+M4)/4ISGRADE<50PRINT“FAIL”STOPYN
- 14.Control StructuresRepresent theflow of logic through the programme.There are four main control structures:• Sequence• Decision – incorporating if-then-else• Repetition• Case
- 15.Sequence Structure• aseries of actions are performed in sequenceSTARTDisplay message“How manyhours did youwork?”Read HoursDisplay message“How much doyou get paid perhour?”Read Pay RateMultiply Hoursby Pay Rate.Store result inGross Pay.Display GrossPayENDThis is the flowchart for a program whichcalculates an employee’s gross pay.
- 16.Example 1 Writean algorithm and draw a flowchart toconvert the length in feet to centimetres.Pseudocode: Input the length in feet (Lft) Calculate the length in cm (Lcm) bymultiplying LFT with 30 Print length in cm (LCM)
- 17.ExampleAlgorithm Step 1:Input Lft Step 2: Lcm Lft x 30 Step 3: Print LcmSTARTInputLftLcm Lft x 30STOPFlowchartPrintLcm
- 18.Example 2Write analgorithm and draw a flowchart thatwill read the two sides of a rectangle andcalculate its area.Pseudocode Input the width (W) and Length (L) of a rectangle Calculate the area (A) by multiplying L with W Print A
- 19.Example 2Algorithm Step1: Input W,L Step 2: A L x W Step 3: Print ASTARTInputW, LA L x WSTOPPrintA
- 20.DECISION STRUCTURES Oneof two possible actions is taken, dependingon a condition.Decision StructureA new symbol, the diamond, indicates a yes/no question.
- 21.Decision Structures Sometimesonly one choice is necessaryYESNO
- 22.Example 1 Pseudocode:StartGetyear bornCalculate agePrint ageIf age > 50 print OLDEnd
- 23. Flowchart StartGet year born Calculate age Print age If age > 50 print OLD EndGet yrCalc agePrint ageAge>50OLDYNStartEnd
- 24.Decision Structure Sometimestwo choices are offered. If the answer to thequestion is yes, the flow follows one path. If the answeris no, the flow follows another pathYESNO
- 25.Decision Structure Inthe flowchart segment below, the question “is x < y?”is asked. If the answer is no, then process A isperformed. If the answer is yes, then process B isperformed.YESNOx < yProcess BProcess A
- 26.IF–THEN–ELSE STRUCTURE Thestructure is as followsIf condition thentrue alternativeelsefalse alternative
- 27.IF–THEN–ELSE STRUCTURE Thealgorithm for the flowchart is asfollows:If A>B thenprint Aelseprint BisA>BPrintAPrintBN Y
- 28.Example 1A ticketseller is issuing show tickets at the gate. When the patrons arrive,he asks how old each one is. It they are under 12, they pay half price. If theyare 12 or over, they pay full price.AlgorithmGet ageAge < 12?If Age < 12ThenPay half priceElsePay full price
- 29.FlowchartYESNOBeginInput ageAge <12Half priceFull priceEnd
- 30.Example 2 Writean algorithm that reads two values, determines thelargest value and prints the largest value with anidentifying message.ALGORITHMStep 1: Input VALUE1, VALUE2Step 2: if (VALUE1 > VALUE2) thenMAX VALUE1elseMAX VALUE2endifStep 3: Print “The largest value is”, MAX
- 31.Example 2MAX VALUE2STOPN YSTARTInputVALUE1,VALUE2MAX VALUE1isVALUE1>VALUE2PrintMAX
- 32.Example 3 Writethe algorithm and draw the flowchartfor the following: Enter two numbers, x and y. If x is lessthan y, square x to give the result a,otherwise, add x + y to give the result a.
- 33.YESNOx < yCalculateaas x times 2.Calculate aas x plus y.AlgorithmInput xInput yx < y?If x <yThena = x^Elsea = x+y
- 34.NESTED IFS Oneof the alternatives within an IF–THEN–ELSE statementmay involve further IF–THEN–ELSEstatement
- 36.Repetition StructureRepetition (Iteration)Structure A repetition structure represents part of the programthat repeats. This type of structure is commonlyknown as a loop.
- 37.Repetition Structure Noticethe use of the diamond symbol. A loop tests acondition, and if the condition exists, it performs anaction. Then it tests the condition again. If thecondition still exists, the action is repeated. Thiscontinues until the condition no longer exists.
- 38.Repetition Structure Inthe flowchart segment, the question “is x < y?”is asked. If the answer is yes, then Process A isperformed. The question “is x < y?” is askedagain. Process A is repeated as long as x is lessthan y. When x is no longer less than y, therepetition stops and the structure is exited.x < y Process AYES
- 39.x < yAdd 1 to xYESSo this might look like…When would this loop exit?
- 40.The action performedby a repetition structure must eventually cause the loop toterminate. Otherwise, an infinite loop is created.In this flowchart segment, x is never changed. Once the loop starts, it will neverend.QUESTION: How can this flowchart be modified so it is no longer an infiniteloop?Out of Control!x < y Display xYES
- 41.This type ofstructure is known as a pre-testrepetition structure. The condition is testedBEFORE any actions are performed.Pre-test ( Before) Loopx < y? Display xAdd 1 to xYES
- 42.Post-test (After) LoopThisflowchart segment shows apost-test repetition structure.The condition is tested AFTERthe actions are performed.A post-test repetition structurealways performs its actions atleast once.Display xAdd 1 to xYESx < y
- 43.Case Structure Oneof several possible actions is taken, depending onthe contents of a variable. Used for MORE THAN TWO decisions
- 44. The structurebelow indicates actions toperform depending on the value inyears_employed.CASEyears_employed1 2 3 Otherbonus = 100 bonus = 200 bonus = 400 bonus = 800
- 45.CASEyears_employed1 2 3Otherbonus = 100 bonus = 200 bonus = 400 bonus = 800If years_employed = 1,bonus is set to 100If years_employed = 2,bonus is set to 200If years_employed = 3,bonus is set to 400If years_employed isany other value, bonusis set to 800
- 46.Case AlgorithmInput aGradeCase based on GradeCase =100Report “Perfect Score” (or suitable command eg Grade = Perfect)Case > 89Report “Grade = A”Case > 79Report “Grade = B”Case > 69Report “Grade = C”Case > 59Report “Grade = D”Default (or Else)Report “Grade = F”End CaseDraw the Flowchart for the above example
- 47.CASEgrade>89 >79 >69> 59Grade =A Grade = B Grade = C Grade = DFlowchartGrade = Perfect Grade = F100 other
- 48.Construct the algorithmand the flowchart for thefollowing procedure:An egg packing business needs to devise aprocess to sort eggs for delivery to supermarkets.If the eggs weigh 50 grams, they are Class Aeggs. If they weigh 60 grams, they are Class Beggs. If they weigh 70 grams, they are Class Ceggs. If they weigh more than 70 grams, they areClass D eggs.
- 49.Input a WeightCasebased on WeightCase =50Class = ACase =60Class = BCase = 70Class = CCase > 70Class = DORDefault/ Else Class = DEnd CaseAlgorithmCASEweight50 60 70 > 70Class =A Class = B Class = C Class = DFlowchart
- 50.Modules (stepwise refinement)Aprogram module is a part of a program thatmakes sense on its own, just like a paragraphin an essay should make sense on its own. Inlarge programs, such as those used inindustry, programs are developed asseparate modules and then put together.The process of representing modules inflowcharts is known as stepwise refinement.You will look at this more closely when youstart programming.
- 51.•The position ofthe modulesymbol indicates the point themodule is executed.•A separate flowchart can beconstructed for the module.STARTENDRead Input.Call calc_payfunction.Display results.STARTDisplay message“How manyhours did youwork?”Read HoursDisplay message“How much doyou get paid perhour?”Read Pay RateMultiply Hoursby Pay Rate.Store result inGross Pay.Display GrossPayEND
- 52.A simpler example…could look likeCASEweight50 60 70 > 70Class =A Class = B Class = C Class =DInput weightCalculate classDisplay class
- 53.A complete programexampleWhen you use stepwise refinement, the complete, refined flowchart is drawn first.Then the modules are named and drawn in order.This program lists the AFL team name and points total for all teams that have a full-forward from the AFL competitionwho has kicked at least 10 goals.
- 54.
- 55.MainLoopAFLGoals >= 10CheckgoalsCheckposCheck goalsCheck conf
- 56.FinishAlthough this procedureis listed as a module in the opening flow chart, it’sunsuitable. Why?