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What is a Problem?

A problem is a circumstance for which we need to develop a solution to get to some goal or provide the means to some end.

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Types of Problems

Informal Problemswe do NOT necessarily find solutions by precisely specifying the initial conditions, the desired results, or the actions (process) by which we achieve the desired results

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Types of Problems

Formal Problems – the kind that can be solved by writing a program for a computer

Problems of synthesis: have specific initial conditions and specific plans of actions (processes), but specify only the general form of the result {Trip: Jax, drive, West Coast}Problems of analysis: the initial conditions and results are known, but not a specific plan of action (process) {Trip: Jax, L.A.}

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Types of Problems

***All problems solved with the aid of computers are problems of synthesis

***The programmer transforms the problem from one of analysis to one of synthesis

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Solving a Problem

1. Understand the problem2. Devise a plan – major steps to accomplish our goal

Divide the problem into segmentsDesign a solutionConsider alternatives and refine solution

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Solving a Problem

3. Carry out the plan (implement)4. Look back

Did you really solve the problem? If not, return to Step 1

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7 Steps in Program Development

Define the problemUse a Defining Diagram

Inputs

Outputs

Processing steps to produce the required output

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7 Steps in Program Development

Outline the solutionBreak the problem up into smaller steps

Major processing steps involved

Major subtasks

Major control structures (e.g. repetition loops)

Major variables and record structures

Mainline Logic

Use a hierarchy or structure chart

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7 Steps in Program Development

Develop the outline into an algorithm

An algorithm is a set of precise steps that describe exactly the tasks to be performed and the order in which they are to be carried outThink ‘recipe for making French toast as given to a robot cook’Pseudocode is how we represent algorithms

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7 Steps in Program Development

Test the algorithm for correctnessDesk checking to identify logic errors

Walk through each step of the algorithm

Keep track of all major variables

Use sample data that tests boundary conditions

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7 Steps in Program Development

Code the algorithm into a specific programming language

NEVER approach the keyboard without a planCode-as-you-go results in wasted time and effort

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7 Steps in Program Development

Run the program with test dataSyntax errors show up at compile time

Typos, punctuation, grammar

Logic errors appear at run time2 + 3 = 6???

Sometimes undetected if testing isn’t thorough

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7 Steps in Program Development

Document and maintain the programExternal documentation

Hierarchy or structure charts, pseudocode, test data and sample results

Internal documentation‘Flower Boxes’ at the beginning of each module or functionInline comments describing the variables and what should be happeningSample program following COBOL Standards

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Structured Programming

Top-down DevelopmentStart out with a general solutionBreak down the solution into more detailed steps (modules)Step-wise refinement – moving from general to specific

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Structured Programming

Modular DesignGroup similar tasks together

Reading a file, checking for end of file, verifying the item read is valid

Printing page headings or totals

Enables several people to work as a team, with each person working on a separate function

Input/Output

Sorting, Updating

Calculating

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Structured Programming

The Structure TheoremEliminated the GOTO statementAll programs can be written with 3 basic control structures

Sequence

Selection, or IF-THEN-ELSE

Repetition, or DO-WHILE

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Algorithm to add two numbers

CalculatorTurn onPress 1st numberPress ‘+’Press 2nd numberPress ‘=‘

ComputerInput 1st numberInput 2nd numberAddPrint result (sum)

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Pseudocode

Structured English used to express an algorithm

Use indentation for logical flowOne instruction per line

Six basic algorithm structures – roughly matching the six basic computer operations

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Pseudocode

Getting data into the computerRead student name {from a file}Get system date {from the system}Read number_1, number_2 {file}Get tax_code {from the keyboard}

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Pseudocode

Getting results from the computer

Print ‘Program Completed’ {printer}Write customer record to file {disk}Display ‘End of Data’ {screen}

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Pseudocode

Doing the mathAdd number to totaltotal = total + numberCompute C = (F – 32) * 5/9Symbols okay to use: +, -, *, /, (, )

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Pseudocode

Assigning a value to a variableSet Count to 0Initialize Totals to zeroTotal = cost + tax

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Pseudocode

Comparing two variablesIf-Then-ElseIF Student is part-time THEN

Add 1 to part-time count

ELSEAdd 1 to full-time count

ENDIF

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Pseudocode

Repeat a group of actions: DO-WHILE, FOR Loop, DO Loop

WHILE student_total < 50 DORead student recordPrint student name, address to reportAdd 1 to student_total

ENDWHILE

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Developing an algorithm

Define the problem

INPUT Processing OUTPUT

Number_1Number_2Number_3

Read 3 numbersAdd numbers togetherPrint total number

Total