ITM207 Exam Notes- Ch 7.docx

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Ryerson University
Information Technology Management
ITM 207
Jim Tam

Problem solving The act of finding a solution to a perplexing, distressing, vexing, or unsettled question How do you solve a problem Understand the problem Devise a plan Carry out the plan Look Back Strategies *Ask Questions but *Never reinvent the wheel!  What do I know about the problem?  What is the information that I have to process in order the find the solution?  What does the solution look like?  What sort of special cases exist?  How will I recognize that I have found the solution? *Ask Questions but *Never reinvent the wheel! - Similar problems come up again and again - A good programmer recognizes a task/subtask that has been solved before and plugs in solution *Divide and Conquer - Break up a large problem into smaller units and solve each smaller problem - Applies the concept of Abstraction - Approach can be applied over and over until each subtask is manageable Computer Problem Solving Summary of Methodology Analyze the Problem Understand the problem!! Develop a plan of attack List the Main Tasks (becomes Main Module) Restate problem as a list of tasks (modules) Give each task a name Write the Remaining Modules Restate each abstract module as a list of tasks Give each task a name Re-sequence and Revise as Necessary Process ends when all steps (modules) are concrete Algorithms  A set of unambiguous instructions for solving a problem or subproblem in a finite amount of time using a finite amount of data Algorithms with Selection E.x. 1. Write “Enter Temperature” 2. Read Temperature 3. Determine what to wear. IF (temperature > 90) Write “Texas weather: wear shorts” ELSE IF (temperature > 70) Write “Ideal weather: short sleeves are fine” ELSE Write “Stay inside” Abstract Step An algorithm step with unspecified details Concrete Step An algorithm step with all details specified Developing Algorithms (to solve a computer problem) Top-Down Design- Focuses on tasks to be done Object-Oriented Design- Focuses on that data involved in the solution Control Structure- An instruction that determines the order of execution of instructions in a program Looping Statements Count-Controlled Loop- A count-controlled loop is a condition-controlled loop with predictable number of iterations. The loop starts at some number (usually the topmost number or zero), then counts down until it reaches the limit (usually zero or the topmost number), at which point it exits the loop. The other common type starts at zero or one, and increments until it reaches a destination number. Set sum to 0 Set count to 1 While (count <= limit) Read number Set sum to sum + number Increment count Write "Sum is " + sum Event-Controlled Loop- In computer science, the event loop, message dispatcher, message loop, message pump, or run loop is a programming construct that waits for and dispatches events or messages in a program. It works by making a request to some internal or external "event provider" (which generally blocks the request until an event has arrived), and then it calls the relevant event handler ("dispatches the event"). Set sum to 0 Set allPositive to true WHILE (allPositive) Read number IF (number > 0) Set sum to sum + number ELSE Set allPositive to false Write "Sum is " + sum Calculating Square Root Read in square Calculate the square root Write out square and the square root Set epsilon to 1 WHILE (epsilon > 0.001) Calculate new guess Set epsilon to abs(square - guess * guess) Calculate Guess Set newGuess to (guess + (square/guess)) / 2.0 End Read in square Set guess to square/4 Set epsilon to 1 WHILE (epsilon > 0.001) Calculate new guess Set
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