CSC 211 Data Structures Lecture 1 Dr Iftikhar

CSC 211 Data Structures Lecture 1 Dr. Iftikhar Azim Niaz ianiaz@comsats. edu. pk 1

Dr. Iftikhar Azim Niaz n B. Sc (Maritime Studies) 1988 q q q n M. Sc (Computer Science) 1994 q n Allama Iqbal Open University Ph. D (Software Engineering) 2005 q n Quaid-i-Azam University MBA (Marketing) 1999 q n Pakistan Marine Academy, President’s Gold Medalist Karachi University of Tsukuba, Japan PGD (Professional Ethics and Teaching Methodology) 2010 q Riphah International University 2

Dr. Iftikhar Azim Niaz n Deck Officer q n n n Sep 1995 – Jan 2007 Quaid-i-Azam University Head of Department Jan 2007 – Feb 2012 q n Apr 1995 – Aug 1995 National Institute of Electronics Lecturer q Mar 1994 – Mar 1995 Deutsche Telepost Consultants, Islamabad Deputy Manager q n Atlas Shipmanagement Limited, Hong Kong System Analyst q Feb 1989 – Feb 1991 Riphah International University Assistant Professor Feb 2012 to Date q q COMSATS Institute of Information Technology Islamabad Campus 3

Why? Why are you studying Data Structure and Computer Science ? 4

Are these your Motivations? n Motivations is a feeling of enthusiasm, interest, or commitment that makes somebody want to do something, or something that causes such a feeling § n n n Encarta Dictionary Because many people take it Just a random choice, no particular reasons A required course I failed CSC 211 before; Want to be taught by a tough instructor More … 5

I believe your REAL motivation is. . . I take it because I am interested 6

Course Details n Course Code: CSC 211 n Course Title: Data Structures n Credit Hours: 3+1 Course Prerequisites CSC 141 Course Objectives: The course is designed to teach students structures and schemes, which allow them to write programs to efficiently manipulate, store, and retrieve data. n n 7

Course Description n n In recent years the subject of computer programming has been recognized as a discipline whose mastery is fundamental and crucial to the success of many engineering projects and which is amenable to scientific treatment and presentation. It has advanced from a craft to an academic discipline it is abundantly clear that a systematic and scientific approach to program construction primarily has a bearing in the case of large, complex programs which involve complicated sets of data. Hence, a methodology of programming is also bound to include all aspects of data structuring. 8

Course Objectives n n n To extend and deepen the student's knowledge and understanding of algorithms and data structures and the associated design and analysis techniques To examine previously studied algorithms and data structures more rigorously and introduce the student to "new" algorithms and data structures. It focuses the student's attention on the design of program structures that are correct, efficient in both time and space utilization, and defined in terms of appropriate abstractions. 9

Course Goals n Upon completion of this course, a successful student will be able to: q q q Describe the strengths and limitations of linear data structures, trees, graphs, and hash tables Select appropriate data structures for a specified problem Compare and contrast the basic data structures used in Computer Science: lists, stacks, queues, trees and graphs Describe classic sorting techniques Recognize when and how to use the following data structures: arrays, linked lists, stacks, queues and binary trees. Identify and implement the basic operations for manipulating each type of data structure 10

Course Goals n Upon completion of this course, a successful student will be able to: q q q Perform sequential searching, binary searching and hashing algorithms. Apply various sorting algorithms including bubble, insertion, selection and quick sort. Understand recursion and be able to give examples of its use Use dynamic data structures Know the standard Abstract Data Types, and their implementations Students will be introduced to (and will have a basic understanding of) issues and techniques for the assessment of the correctness and efficiency of programs. 11

Course Outline - I n n n n n Introduction to data structures Linear and non-linear data structures Arrays and pointers List data structure Singly linked list Doubly linked list Analysis of List data structures Circular linked list Stack; Implementation of stack using arrays and linked list Applications of a stack 12

Course Outline - II n n n n n Infix to postfix conversion Evaluation of postfix expressions Queues; Implementation of queues using arrays and linked list Circular Queues; Priority Queues; Tree traversals; Binary search trees and implementation Heaps and Heap sort; Graphs; Minimum spanning trees; Hashing Files 13

Recommended Books Textbooks: n R. Kruse, C. L. Tondo, B. Leung Data Structures & Program Design in C, 2 nd Edition, Pearson Education Inc. India , 2007 n Mark A. Weiss, Data Structures and Algorithm Analysis in C, 2 nd Edition, Pearson Education Inc. India, 1997. Reference Books: n Debasis Samanta, Classic Data Structures, 2 nd Edition, Prentice Hall India, 2009 n ISRD Group, Data Structures Using C, Tata Mc. Graw-Hill Publishing Company, New Delhi, India, 2006. 14

Recommended Text Books 15

Recommended Text Book 16

Marks Distribution of Course n Assignments ……… 15% n Quizzes . . ……………. . 10% n Sessionals . …………. …. . 25% n Final . ……………… 50% 17

A Nice Quote Want to get something in life Always think positive You will definitely get the thing you want 18

A nice saying I keep 6 honest serving men. They taught me all I knew. Their names are: WHAT and WHY and WHEN and HOW and WHERE and WHO. (R. Kipling) And believe me, on the road of learning, these are your best companions. 19

Five Tips to Success n Work Hard n Try More exercises and more practice n Do the Labs and assignments by yourself 20

Five Tips n Be patient with the Machine n If you really need that, do it quietly 21

Is the same situation is with you? yes No 22

Boss assigns task q To perform certain task? How u will do? 23

Your Question: n Um? Tell me what to code. 24

So your answer: n I can develop a new algorithm for you. Great thinkers will always be needed. 25

Study: n Many experienced programmers were asked to code up binary search. 80% got it wrong Good thing is was not for a nuclear power plant. 26

What did they lack? n Fundamental understanding of the algorithmic design techniques. 27

Programming is Problem Solving n n Programming is a process of problem solving Problem solving techniques n n n Analyze the problem Outline the problem requirements Specify what the solution should do Design steps, called an algorithm, to solve the problem (the general solution) Verify that your solution really solves the problem Algorithm – a step-by-step problem-solving process in which a solution is arrived at in a finite amount of time 28

Computer Programming n Nicklaus Wirth Program = Algorithm + Data Structure n n n Computer programming involves writing software that allows a machine to perform various tasks which, by hand, would be tedious or so time consuming as to be essentially impossible to do. Machines work incredibly quickly, never get tired, and are excellent at following orders; however, they will only perform as well as the instructions presented to them. Set of instructions that tell the computer what to do and how to do? 29

Introduction to Problem Solving n n Programming is a problem solving activity. When you write a program, you are actually writing an instruction for the computer to solve something for you. Problem solving is the process of transforming the description of a problem into a solution by using our knowledge of the problem domain and by relying on our ability to select and use appropriate problem-solving strategies, techniques and tools. 30

Case Study: Yummy Cupcake n Problem: You are required to calculate the amount to be paid by a customer buying cupcakes. 31

Software Development Method (SDM) n For programmer, we solve problems using Software Development Method (SDM), which is as follows: 1. 2. 3. 4. 5. 6. Specify the problem requirements. Analyze the problem. Design the algorithm to solve the problem. Implement the algorithm. Test and verify the completed program. Documentation 32

1. Requirement Specification n n Specifying the problem requirements requires you to state the problem clearly and to gain the understanding of what to be solved and what would be the solution. When specifying problem requirement, we ask ourselves the following questions: q q What the problem is. What the solution should provide. What is needed to solve it. If there are constraints and special conditions. 33

Yummy Cupcake Problem: You are required to calculate the amount to be paid by a customer buying cupcakes. q What the problem is. q What the solution should provide. q What is needed to solve it. q If there are constraints and special conditions. 34

Problem Analysis n Analyzing the problem require us to identify the following: q q Input(s) to the problem, their form and the input media to be used Output(s) expected from the problem, their form and the output media to be used Special constraints or conditions (if any) Any formulas or equations to be used 35

Yummy Cupcake n Input? q Quantity of the cupcake purchased (integer) q Price per cupcake (RM, float) n Output? q Total amount to be paid by the customer (RM, float) n Constraint/condition? q Quantity purchased must be more than zero q Price per cupcake must be more than zero (it is not free) q We assume that the price given is the standard price to all cupcakes n Formula/equation? q Amount to pay = quantity of cupcake x price per cupcake 36

Designing algorithm n n Designing algorithm to solve the problem requires you to develop a list of steps, arranged in a specific logical order which, when executed, produces the solution for a problem. Using top-down design (also called divide and conquer): q q n You first list down the major tasks For each major task, you further divide it into subtasks (refinement step) When you write algorithm, write it from the computer’s point of view. 37

Designing Algorithm cont. . n An algorithm must satisfy these requirements: q q q q It may have an input(s) It must have an output(s) It should not be ambiguous (there should not be different interpretations to it. Every step in algorithm must be clear as what it is supposed to do) It must be general (it can be used for different inputs) It must be correct and it must solve the problem for which it is designed It must execute and terminate in a finite amount of time It must be efficient enough so that it can solve the intended problem using the resource currently available on the computer 38

Yummy Cupcake Major Task: 1. Read the quantity of cupcake purchased 2. Read the price per cupcake 3. Calculate total amount to pay 4. Display the total amount to pay However, looking at the above algorithm, we can still further refine step 3, by introducing the formula to calculate the amount to pay. After refinement: 1. Read the quantity of cupcake purchased 2. Read the price per cupcake 3. Total amount to pay = quantity of cupcake x price per cupcake 4. Display the total amount to pay 39

Remember, the order of the steps in algorithm is very important. Consider the following, will the result be the same? 1. 2. 3. 4. Display the total amount to pay Get the quantity of cupcake purchased Total amount to pay = quantity of cupcake x price per cupcake Get the price per cupcake 40

Control Structure n n An algorithm can be represented using Pseudocode or Flowchart. In 1966, two researchers, C. Bohn and G. Jacopini, demonstrated that any algorithm can be described using only 3 control structures: sequence, selection and repetition. 41

Control Structure n n n Sequence: A series of steps or statements that are executed in the order they are written in an algorithm. Selection: Defines two courses of action depending on the outcome of a condition. A condition is an expression that is, when computed, evaluated to either true or false. Repetition: Specifies a block of one or more statements that are repeatedly executed until a condition is satisfied. 42

What is an Algorithm? There are two parts to a computer program. q There is the process or sequence of steps which are necessary to complete the given task and q the translation of this process into a language which the computer can understand. q 43

Algorithm (Definition) n n n An algorithm refers to a step-by-step method for performing some action. A precisely defined sequence of (computational steps) that transform a given input into a desired output. An algorithm tells us how to perform a task. The logical steps to solve a problem. Some examples of algorithms in everyday life are food preparation, directions for assembling equipment or instructions for filling out income tax forms. 44

Criteria for Algorithm n n n Input: Zero or more quantities are externally supplied Output: At least one desired result is produced Definiteness: Each instruction must be clear and unambiguous Finiteness: Algorithm terminates after a finite number of steps Effectiveness: Each instruction must be feasible and very basic 45

From Algorithms to Programs Problem Algorithm: Algorithm A sequence of instructions describing how to do a task Computer Program 46

Algorithm Representation Algorithm Pseudocode Flow Chart 47

What is Pseudocode? n n Traditionally, flowcharts were used to represent the steps in an algorithm diagrammatically. These were bulky, difficult to draw and often led to poor program structure. Pseudocode is the method of writing down an algorithm. Pseudocode is easy to read and write. It represents the statements of an algorithm in English like language. Pseudocode is really structured English. It is English which has been formalised and abbreviated to look like very high level computer languages. 48

Pseudocodes n A pseudocode is a semiformal, Englishlike language with limited vocabulary that can be used to design and describe algorithms. n Criteria of a good pseudocode: q q q Easy to understand, precise and clear Gives the correct solution in all cases Eventually ends 49

Example of Pseudocode 1. Open freezer door 2. Take out Meal 3. Close freezer door 4. Open microwave door 5. Put Meal on carousel 6. Shut microwave door 7. Set microwave on high for 5 minutes 8. Start microwave 9. Wait 5 minutes 10. Open microwave door 11. Remove Meal 12. Close microwave door 50

Example of Algorithm procedure Do_Thursday { Wake_up ; Take_A_Shower ; Eat_Breakfast ; Drive_To_university ; Attend_ALGO_Lecture ; . . . etc. . . Drive_From_university ; . . . etc. . . } procedure Do_Week { Do_Monday ; Do_Tuesday ; Do_Thursday ; . . . etc. . . } 51

Pseudocode n Pseudocode = English + Code relaxed syntax that is easy to read extended version of the basic control structures (sequential, conditional, iterative) 52

Pseudocode Rules n n n n There is currently no standard pseudocode. There are however certain conventions: Statements are written in simple English; Each instruction is written on a separate line; Logic-showing Keywords are written in UPPER CASE (e. g. IF , THEN, FOR, WHILE ) Each set of instructions is written from top to bottom with only one entry and one exit; Groups of statements may be formed into modules, and that group given a name. 53

Pseudocode n n n The following conventions are usually used. The symbol ► is used to indicate that the reminder of a line should be treated as a comment. If more than one statement appears on a single line, a semicolon will be used to separate them. ASSIGNMENT STATEMENTS have the form x ← e, which assigns the value of expression e to variable x. Multiple assignments can be performed in one statement; for example, x ← y ← e assigns the value of e to variables x and y. 54

Pseudocode n n n Another way do this as follows: x : = e where x is a variable and e is an expression. When an assignment statement is executed, q q the expression e is evaluated (using the current values of all variables in the expression), and then its value is placed in the memory location corresponding to x (replacing any previous contents of this location). 55

Transposing Two Values n Example Find an algorithm that takes two values x and y n n n as inputs. The input values are, then, interchanged to obtain the output. Method: If we try x : = y y : =x We would not obtain the desired output. Step 1 correctly changed x but the original value of x was lost. Step 2 has no effect on the value of y. To obtain the desired results, we must save the original value of x. 56

Transposing Two Values To obtain the desired results, we must save Example 1. 2. 3. 4. 5. the original value of x. This is done by assigning the value of x to a new variable called Save. Input x, y [Input the values] Save : = x [Storing the original x] x : = y [Part of the output] y : = Save [The original x value] Output x, y [Values Transposed] 57

Flowcharts n Flowcharts is a graph used to depict or show a step by step solution using symbols which represent a task. n The symbols used consist of geometrical shapes that are connected by flow lines. n It is an alternative to pseudocoding; whereas a pseudocode description is verbal, a flowchart is graphical in nature. 58

Flowchart Symbols Terminal symbol - indicates the beginning and end points of an algorithm. Process symbol - shows an instruction other than input, output or selection. Input-output symbol - shows an input or an output operation. Disk storage I/O symbol - indicates input from or output to disk storage. Printer output symbol - shows hardcopy printer output. 59

Flowchart Symbols cont… Selection symbol - shows a selection process for two-way selection. Off-page connector – provides continuation of a logical path on another page. On-page connector - provides continuation of logical path at another point in the same page. Flow lines - indicate the logical sequence of execution steps in the algorithm. 60

The Sequence control A series of steps or statements that are executed in the structure order they are written in an algorithm. n n The beginning and end of a block of statements can be optionally marked with the keywords begin and end. begin statement 1. statement 2. … … statement n. end begin statement 1 statement 2 … statement n end 61

The Sequence control structure Problem: calculate a person’s age Begin read birth year age = current year – birth year display age End begin read birth year Age = current year – birth year Display age end 62

The Selection control Defines two courses of action depending on the structure outcome of a condition. A condition is an expression n that is, when computed, evaluated to either true or false. The keyword used are if and else. Format: if (condition) then-part else-part end_if No elsestatement(s) Condition? Yes thenstatement(s) 63

The Selection control Beginstructure read age if (age is greater than 55) print “Pencen” else print “Kerja lagi” end_if End Begin read age if (age > 55) print “Pencen” else print “Kerja lagi” end_if End Begin Read age YES age > 55? NO print “Kerja lagi” print “Pencen” End 64

Pseudocodes: The Selection control Sometimes in certain situation, we may omit the else-part. structure n if (number is odd number) print “This is an odd number” end_if n Example 1 Nested selection structure: basic selection structure that contains other if/else structure in its then-part or else-part. if (number is equal to 1) print “One” else if (number is equal to 2) print “Two” else if (number is equal to 3) print “Three” else print “Other” end_if Example 2 65

Exercise Draw the flowchart diagram for Example 1 and Example 2 66

The Repetition control structure n n n Specifies a block of one or more statements that are repeatedly executed until a condition is satisfied. The keyword used is while. Format: while (condition) loop-body end_while Condition? yes Loop Statement(s) no 67

Problem: Write a program that reads and displays the age of 10 people (one after another). For this problem, we need a way to count how many people whose age have been processed (read and displayed). Therefore, we introduce a concept of counter, a variable used to count the number of people whose age have been processed by the program. 68

Counter initialisation Begin number of users giving his age = 1 while (number of users giving his age <= 10) read the age from the user. Loop condition print the user age. number of user giving his age + 1 end_while Updating counter End Begin users = 1 while (users <= 10) read age print age. users = users + 1 end_while End 69

Begin users = 1 NO End users <= 10? YES read age print age users =users + 1 70

Subsequently. . You can start the Begin counter with ZERO number of users giving his age = 0 while (number of users giving his age < 10) read the age from the user. print the user age. The loop condition number of user giving his age + 1 must less than the end_while value it requires to End stop Begin users = 0 while (users < 10) read age print age. users = users + 1 end_while End Be consistent 71

Little extra… n n Now let us put together everything that you have learnt so far. Problem: Write a program that will calculate and print the age of 10 persons, given their birth year. If the age of the person is above 55, then the program will print “Pencen”, otherwise, the program will print “Kerja lagi”. 72

Begin users = 1 Example 3 while (users <= 10) begin Read birth year age = current year – birth year print age Note that in this if age > 55 example, we are print “Pencen” using all the three else control structures: print “Kerja lagi” sequence, selection end_if and repetition users = users + 1 end_while End 73

Exercise Draw the flowchart diagram for Example 3 74

Implementation n The process of implementing an algorithm by writing a computer program using a programming language (for example, using C language) n The output of the program must be the solution of the intended problem n The program must not do anything that it is not supposed to do (Think of those many viruses, buffer overflows, trojan horses, etc. that we experience almost daily. All these result from programs doing more than they were intended to do) 75

Testing and Verification n Program testing is the process of executing a program to demonstrate its correctness n Program verification is the process of ensuring that a program meets userrequirement n After the program is compiled, we must execute the program and test/verify it with different inputs before the program can be released to the public or other users (or to the instructor of this class) 76

Documentation n Writing description that explain what the program does. n Can be done in 2 ways: q Writing comments between the line of codes q Creating a separate text file to explain the program n Important not only for other people to use or modify your program, but also for you to understand your own program after a long time (believe me, you will forget the details of your own program after some time. . . ) 77

Documentation cont… n Documentation is so important because: q q q n You may return to this program in future to use the whole of or a part of it again Other programmer or end user will need some information about your program for reference or maintenance You may someday have to modify the program, or may discover some errors or weaknesses in your program Although documentation is listed as the last stage of software development method, it is actually an ongoing process which should be done from the very beginning of the software development process. 78

Exercise time!!! 79

Volume calculation Write a pseudocode and a flowchart for a C program that reads the value of height, width and length of a box from the user and prints its volume. 80

Calculating Electricity Bills The unit for electricity usage is k. Wh. For domestic usage, the monthly rate is 21. 8 cents/unit for the first 200 unit, 25. 8 cents/unit for the next 800 units and 27. 8 cents/unit for each additional units. Given the amount of electricity units (in k. Wh) used by a customer, calculate the amount of money needs to be paid by the customer to TNB. A bill statement needs to be printed out. Write a pseudocode or a flow chart to solve the above problem. 81

Sum of 1 to 10 Write a pseudocode or flowchart for a program that would compute and print the sum of all integers between 1 and 10. 82

Summary n n Course Description, Goals and Contents Introduced the concept of problem solving : a process of transforming the description of a problem into a solution. n A commonly used method – SDM which consists of 6 steps n 3 basic control structures : sequence, selection and repetition structures n Pseudocode and Flow chart 83