CS10051 Section 600Introduction

to Computer Science

Fall 2010

Dr. Angela Guercio

Prof. Kathleen Stirbens

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Objectives

In this chapter, you will learn about:

The definition of algorithm

The definition of computer science

Overview of the course

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What is an Algorithm?

An algorithm is a well-ordered collection of unambiguous and effectively computable operations that, when

executed, produces a result and halts in a finite amount of time.

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Example of Algorithm

An algorithm is a list that looks like STEP 1: Do something STEP 2: Do something STEP 3: Do something . . . . . . STEP N: Stop, you are finished

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The Formal Definition of an Algorithm

Algorithm A well-ordered collection of unambiguous and

effectively computable operations that, when executed, produces a result and halts in a finite amount of time

Example: Make Pasta1. Boil two quarts of water

2. Add ½ lb of pasta in the water

3. Strain the water

4. Add the sauce

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The Formal Definition of an Algorithm (continued) Unambiguous operation

An operation that can be understood and carried out directly by the computing agent without needing to be further simplified or explained

Ex. Boil some water (ambiguous) Boil 2 quarts of water (unambiguous)

An operation that is unambiguous is called a primitive operation (or just a primitive) Q. - What are the primitives of a computer? A. -

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The Formal Definition of an Algorithm (continued)

Effectively computable Computational process exists that allows computing

agent to complete that operation successfully Note that a given collection of operations may be an

algorithm with respect to one computing agent, but not with respect to another computing agent!!

Example of not effectively computable operations: Write all the real numbers between 0 and 1.

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The Formal Definition of an Algorithm (continued)

The result of the algorithm must be produced after the execution of a finite number of operations

i.e. Can the user of the algorithm observe a result produced by the algorithm?

A result can be a sign, a sound, an alarm, a number, a message of error, ect…

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The Formal Definition of an Algorithm (continued) It halts in a finite amount of time.

Infinite loop The algorithm has no provisions to terminate A common error in the designing of algorithms

Do not confuse, "not finite" with "very, very large".

Q. - Is this loop “finite”, “infinite”, or “very, very large”?Step 1. Write the number 1 on the board.Step 2. Add 1 to the number you just wrote and write the result

on the boardStep 3. Repeat Step 2.Step 4. Stop.

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The Importance of Algorithmic Problem Solving Algorithmic solutions can be:

Encoded into some appropriate language Given to a computing agent to execute

The computing agent Would mechanically follow these instructions and

successfully complete the task specified Would not have to understand

Creative processes that went into discovery of solution Principles and concepts that underlie the problem

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Which of those is an algorithm? Write all the possible numbers on a paper. Fill 1 cup of sugar. Mix it to 3 cups of milk. Think of a number. Add 20 to it. Either wet your hair or lather your hair.

Then rinse your hair. If your hair are dirty, wet your hair; lather

your hair; rinse your hair; else go back to study.

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Common misconceptions about Computer Science

Misconception 1

Computer science is the study of computers

Misconception 2

Computer science is the study of how to write computer programs

Misconception 3

Computer science is the study of the uses and applications of computers and software

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The Definition of Computer Science Computer science is the study of algorithms

including

1. Their formal and mathematical properties 2. Their hardware realizations 3. Their linguistic realizations 4. Their applications

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1. Their formal and mathematical properties

It is not enough to design an algorithm to solve a problem.

We must worry about some additional properties of an algorithm: How efficient is it? What kinds of resources must be used to execute

it? How does it compare to other algorithms that solve

the same problem?

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2. Their hardware realizations Computing entities are required to execute

algorithms Computing entities are not necessarily machines! However our interest will lie with algorithms that execute

on computing entities called "computers". How are computer constructed?

The emphasis of the course will be on the logical construction of a computer, not the physical construction.

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3. Their linguistic realizations Which language do we use to code the

algorithms? We will start with one linguistic realization,

called pseudocode and later will look at possible different realizations in various programming languages.

In particular we will do some introductory programming in C++.

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4. Their applications

What are some of the many important and popular applications of computers in current use including: numerical problem solving information retrieval graphics networking artificial intelligence telecommunications modeling and simulation

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Overview of the course 1. The algorithmic foundations of computer science. (Ch 1-3) 2. The hardware world. (Ch 4-5) 3. The virtual machine. (Ch 6-7) 4. The software world. (Ch 8-11) 5. Applications. (Ch 12-14) 6. Social issues. (Ch 15)

Note these correspond to the levels of the pyramid on the cover of your text.

Each level addresses one aspect of the definition of computer science

Computer science/Algorithms

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Figure 1.9Organization of the Text into a Six-Layer Hierarchy

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Summary Computer science is the study of algorithms

An algorithm is a well-ordered collection of unambiguous and effectively computable operations that, when executed, produces a result and halts in a finite amount of time

If we can specify an algorithm to solve a problem, then we can automate its solution

Computers developed from mechanical calculating devices to modern electronic marvels of miniaturization

BE SURE TO CHECK THE CLASS WEBSITE DAILY FOR YOUR:

Reading assignmentsHomework assignmentsOther materials related to this course

http://www.personal.kent.edu/~aguercio/Fall10/CS10051-600Fa10.html