Problem Solving Methods CSCE 106 Outline n Problem

Problem Solving Methods CSCE 106

Outline n Problem Solving Methods n Problem solving steps n The analytical method n The algorithmic method n The software engineering method n Exercise - applying software engineering method n Flow chart symbols I CSCE 106 2

Problem Solving Methods n n n There is no perfect method for solving all problems. There is no problem-solving computer to which we could simply describe a given problem and wait for it to provide the solution. Problem solving is a creative act and cannot be completely explained. However, we can still use certain accepted procedures to structure our thinking and help us solve problems. Three methods of problem solving are prominent: 1. Analytic Method. 2. Algorithmic Method. 3. Software Engineering Method. CSCE 106 3

Problem Solving Steps Each method has four basic components: 1. Problem: the problem presents the situation that requires a solution. 2. Reasoning: this implies a true comprehension of the problem. 3. Solution: this is the process that we develop to solve the problem. 4. Testing: this is the checking process we use to confirm that the solution is correct. CSCE 106 4

The Analytic Method n n Analytic problem solving has roots in mathematics, physics, engineering, chemistry, and a host of other areas in science and technology. Example: Problem The sum of two numbers is s and their product is p. Find the 2 numbers. Reasoning Let us call the first number x and the second one y. Therefore, x + y = s and x * y = p. From the first equation we get: y = s - x. Substituting y from the first equation into the second equation, we get: x * (s - x) = p or x 2 - sx + p = 0. CSCE 106 5

The Analytic Method (cont’d) Solution The solution to this problem is the solution to the quadratic equation: x 2 - sx + p = 0, provided that s 2 - 4 p 0. This solution is known from the field of mathematics. Testing To check the correctness of the above solution we calculate x + y and x * y. CSCE 106 6

The Algorithmic Approach n n n An algorithm could be defined to be a set of steps that defines how a task is performed. The study of algorithms began as a subject in mathematics. The word “algorithm” is derived from the name of the Arab mathematician, Abu Ja’far Mohammed Ibn Musa Al-Khowarizmi (c. A. D. 825), who wrote a book describing procedures for calculating. Today, computer science has established itself as the science of algorithms. Algorithmic Problem An algorithmic problem is any problem whose solution can be expressed as a list of executable instructions. By executable we mean that an independent executor (human or machine) should be able to carry out the instructions in a step–by–step manner. Algorithms are not unique to the computational sciences. An algorithm is a recipe, a sequence of steps that leads from a starting point to a finished product. CSCE 106 7

An Algorithm CSCE 106 8

An Algorithm (cont’d) Examples of Algorithmic Problems: u Backing a cake. u Knitting a sweater. u Taking the sum of a finite list of numbers. u Sorting a finite list of names. u Playing Tic-Tac-Toe. n An algorithm is a sequence of executable instructions with these properties: 1. There is no ambiguity in any instruction. 2. There is no ambiguity about which instruction is to be executed next. 3. The description of the algorithm is finite. 4. Execution of the algorithm concludes after a finite number of steps. n CSCE 106 9

The Algorithmic Approach (cont’d) Non-Algorithmic Problems Consider the following instructions: n Step 1: Step 2: Step 3: Step 4: n Make a list of the odd positive integers. Compute their sum. Compute their average. Print the average. This is not an algorithm because it is impossible to make an infinite list of numbers, and the problem of finding the sum (or average) of all odd positive integers is not algorithmic. CSCE 106 10

Phases of Algorithmic Problem Solving n The following loosely defined problem-solving phases were presented by the mathematician G. Poyla in the late 1940 s. Phase 1: Understand the problem. Phase 2: Devise a plan for solving the problem. Phase 3: Carry out the plan. Phase 4: Evaluate the solution for accuracy and for its potential as a tool for solving other problems. CSCE 106 11

Software Engineering Method n n Software engineering is the area of computer science concerned with building large software systems. Windows 2000 is estimated to have 30 million lines of code. The challenge is that there are tremendous advances in hardware that have not been accompanied by comparable advances in software. Some of the software engineering goals for software reliability, understandability, cost effectiveness, adaptability, and reusability. CSCE 106 12

Software Engineering Phases Problem Analysis - (Correct Problem) u Identify data objects u Goal to model properties u Determine Input / Output data u Constraints on the problem n Design (Pseudocode/Flow Chart) u Decompose into smaller problems u Top-down design (divide and conquer) u Think of algorithm n CSCE 106 13

Software Engineering Phases (cont’d) Implementation u Writing the computer algorithm (e. g. in C++) n Testing u Verify the program meets requirements u System and Unit test n Documentation u Key part in the development process n CSCE 106 14

Exercise - Applying Software Engineering Method n n Problem Analyse, design and implement a C++ program to output the word “Hello!”. Analysis Input Nothing u Output “Hello!” u CSCE 106 15

Exercise (cont’d) n Design n Implementation (C++) #include <iostream> using namespace std; void main () START { cout << "Hello!"; OUTPUT “Hello!” STOP CSCE 106 } 16

Flow Chart’s Symbols I n Terminals u INPUT OUTPUT Any input or output operation n Flow u STOP Start or stop of the program n Input/Output u START lines Indicate the sequence of operations CSCE 106 17

Hello. cpp // FILE: Hello. cpp // DISPLAYS THE WORD “HELLO” TO THE USER #include <iostream> using namespace std; void main () { cout << "Hello!"; } CSCE 106 18

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Next lecture we will continue C++ CSCE 106 20