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ICS102: Introduction To Computing

King Fahd University of Petroleum & MineralsCollege of Computer Science & Engineering

Information & Computer Science Department

Problem Solving 1

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Today’s Class

• What’s Computer Science?

• What’s an Algorithm?

• Problem solving techniques

• Overview of computer programming process

• Problem solving techniques

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What is Computer Science?• It is the discipline that seeks to build a scientific foundation for such

topics as computer design, computer programming, information processing, and algorithmic solutions of problems.

• A computer is a machine that stores data, interact with devices, execute programs, and provides computing capabilities to its users).

• Computing is the execution of an “algorithm”.

What is an Algorithm?

A set of steps that define how a task is performed. In other words, it is an ordered set of unambiguous, executable steps that define a terminating activity.Examples:

• Make a list of all positive integers

• Extract the first integer from the list

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Algorithm• An algorithm can be represented using some sort

of language, such as the flowcharts pseudocode (precisely defined textual structures)

• An algorithm is abstract and it can be represented in many ways.

EXAMPLE:

Algorithm for converting from Celsius to Fahrenheit can be represented as

1. F = (9/5) C + 32 (algebraic equation)

2. “ Multiply the temperature reading in Celsius by 9/5 and then add 32 to the product”

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Example: An algorithm for starting the car

To run the car, we follow the following steps:

1. Insert the key in ignition

2. Make sure transmission is in Park (or Neutral)

3. Depress the gas pedal

4. Turn key to start position

5. If engine starts within six seconds, release key to ignition position

6. If engine does not start in six seconds, release key and gas pedal, wait ten seconds, and repeat steps 3 through 6, but not more than five times

7. If the car does not start, call the garage

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Computer program is a sequence of instructions to be performed by a computer.

Computer programming is the process of planning a sequence of steps for a computer to follow

Programming Process has the following three phases:

• Problem-solving phase

• Implementation phase

• Maintenance phase

Programming Process

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Programming ProcessProblem-solving phase

•Analysis and specification ( understand and define problem, and what is expected of solution)

•General solution (algorithm: a logical sequence of steps that solves the problem)

•Verification (Follow steps to make sure solution solves the problem)

Implementation phase

•Concrete solution (Program in a Programming language)

•Testing (make sure the program produces the desired results)

Maintenance phase

•Use Program

•Maintain Program (meet changing requirements)

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Programming Process

Analysis and Specification

General solution (algorithm)

Verification

Concrete solution

(Program)

Testing

Maintenance Phase

Documentation: writing program documentation, and user manuals

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Problem Solving

• The purpose of writing a program is to solve a problem

• The general steps in problem solving are:

– Understand the problem– Dissect the problem into manageable pieces– Design a solution– Analyze the complexity of the algorithm– Consider alternatives to the solution and refine it– Implement the solution– Test the solution and fix any problems that exist

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• Many software projects fail because the developer didn't really understand the problem to be solved

• We must avoid assumptions and clarify ambiguities

• As problems and their solutions become larger, we must organize our development into manageable pieces

• This technique is fundamental to software development

• In java, we will dissect our solutions into pieces called classes and objects, taking an object-oriented approach

Problem Solving

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Problem Solving Techniques

• You follow algorithms every day in your life. So, we need to learn how to design algorithms not simply follow them.

• So, what is Problem Solving Process?

1. Analysis 2. Design

3. Implementation 4. Testing

Testing

Design

Analysis

Implementation

Determine problem features

Describe objects and methods

Produce the classes and code

Examine for correctness

Rethink as appropriate

Some Strategies to solve problems• Ask questions

• Look for things that are familiar

• Means-Ends Analysis

• Divide and Conquer

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Strategies: Ask Questions

When you are given a problem, you ask questions (What, Why, When, and Where?)

In the context of programming

•What do I have to work with (What is my data)?

•What do the data items look like?

•How much data is there?

•How will I know when I have processed all the data?

•What should my output look like?

•How many times is the process going to be repeated?

•What special error conditions might come up?

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Strategies: Look for Familiar Things

• Never reinvent the wheel

If a solution exists USE IT

Finding the daily high and low temperatures

is really the same problem as

Finding the highest and lowest grades on a test

Both problems can be abstracted as being

Find largest and smallest values in a set of numbers

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Strategies: Means-Ends Analysis

• Beginning state and End state are often given

• You need to define a set of actions that can be used to get from one to the other

• Once you have a set of actions, you need to work out the details

Translated to computer programming

Begin by writing down what the input is? (Beginning state)

What the output should be? (End state)

What actions can be performed to obtain results from input data?

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Strategies: Divide and Conquer

Break up large problems into smaller problems that are easier to handle

(Top-Down approach)

Hard problem

Easy subproblem

Easy subproblem

Hard subproblem

Easy subproblem

Easy subproblem

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An Example

Compute the area of a circle

Problem statement

We need an interactive program (user will input data) that computes the area of a circle. Given the circle radius, the circle area should be displayed on the screen

Input/Output description

Input Circle radius

Output Circle area

Algorithm development (set of steps, decomposition outline)

1. Read value of circle radius (r)

2. Compute circle area as pi* r2

3. Print the value of circle area

How do we represent more complex algorithms

Pseudocode, flowcharts

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An Example (continued)

A divide and conquer block diagram of our problem

Circle area

Read radius Print circle areaCompute area

Pseudocode

Prompt the user for the circle radius (put a message on the screen)

Read radius

Assign Circle area the value pi * radius2

Write Circle area on the screen

Stop