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Flowcharts Problem Solving • Computer programs are written to solve problems or perform tasks • Programmers translate the solutions or tasks into a language the computer can understand • The computer will only do what we instruct it to do • We need to be careful and thorough with our instructions Designing a Computer Program 1. Determine what the output should be 2. Identify the data or input needed to produce that output 3. Determine how to process the input to obtain the desired output Designing a Computer Program • Consider the following problem – How fast is a car travelling if it travels 135 miles in 3 hours 1. What is the type of answer required (the output)? 2. What information (the input) is needed to obtain this output? 3. What is the process that transforms the input into the output? Pictorial Representation Input Processing Output Program Development • Consider the development process or strategy that should be adopted when developing a program similar to the ones you are/have developed in your programming course Program Development 1. Analysis: Define the problem 2. Design: Plan the solution…a logical sequence of precise steps (Algorithm) 3. Implementation: Translate the algorithm into a programming language 4. Testing and Debugging: Locate and remove any errors in the program 5. Complete the documentation Helpful Tools • Converting algorithms into computer programs – Flowcharts – graphically depict the logical steps of the program and show how the steps are related to each other – Pseudocode – Use English-like phrases with some programming terminology to outline the program Flowcharts • Consists of geometric symbols connected by arrows • Within each symbol: a phrase presenting the activity at that step • Shape of symbol: indicates type of operation that is to take place • Arrows connecting symbols (flowlines): show the progression in which the steps take place Flowchart Symbols Flowline Terminal Input/Output Processing Decision Flowchart Symbols Connector Off-page connector Predefined Process The height of the text box and its associated line increases or decreases as you add text. To change the w idth of the comment, drag the side handle. Annotations Postage Stamp Problem • Algorithms are used every day for decision making • Consider the following problem – Any time you post a letter you must decide how much postage to put on the envelope. One rule of thumb might be to use one stamp for every five sheets or fraction thereof. Suppose a colleague asks you to determine the number of stamps they need on an envelope. What algorithm should you adopt? Algorithm for Postage Stamp Problem 1. Request the number of sheets of paper, call it sheets (input) 2. Divide Sheets by 5 (processing) 3. Round the quotient up to the next highest whole number, call it Stamps (processing) 4. Reply with the number Stamps (output) • Display graphically this algorithm, highlighting the input, processing and output • Task: Test the algorithm for letters with different numbers of stamps…. Flowchart for Postage stamp problem Start Read Input Set Stamps=Sheets/5 Round Stamps up to next w hole number Display Stamps End Sequence Structure Pseudocode for Postage Stamp Problem Program: Determine the proper number of stamps for a letter Read Sheets Set the number of stamps to Sheets/5 Round the number of stamps up to the next whole number Display the number of stamps Including decisions in flowcharts IF condition is true THEN No Process Step 1 Is condition True Yes ELSE Process Step 2 Process step 2 END IF Process Step 1 Combine Sequence and Decision Structures • Given a street number of a one-way street in New York, decide the direction of the street – Rule: Even number means Eastbound street • Generate the pseudocode and flowchart for this problem Recall: Input Processing Output Loops in flowcharts WHILE condition is true Process Steps Is Condition True Yes LOOP Process Steps No Problem • Calculate and report the average QCA for the class • Determine – Input – Processing – Output Symbols Preparation (usually used for loops, i.e. the initialisation of variables) In this lecture flowcharts for while, do-while and for loops that use and do not use the preparation symbol will be considered. Links • http://www.eng.iastate.edu/efmd/161algor.htm • http://users.evtek.fi/~jaanah/IntroC/DBeech/3gl_fl ow.htm#exercise1 • http://www.allclearonline.com/applications/Docu mentLibraryManager/upload/program_intro.pdf • http://erc.msh.org/quality/example/exampl11.cfm • http://www.enm.bris.ac.uk/staff/pjn/EMAT10920/ (especially lesson 2) Summary • • • • • • • Problem Solving Designing a Computer Program Input Processing and Output Flowcharts and Pseudocode Flowchart symbols Flowchart sequence and decision Looping in flowcharts