MIS 131 Introduction to Algorithms and Programming 20182019

MIS 131 Introduction to Algorithms and Programming 2018/2019 Fall - Chapter 1 – Algorithms, Pseudocodes and Flowcharts © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved. 1

2 Objectives • In this chapter, you will learn: – – To understand basic problem solving techniques. Inputs and outputs of a proglem Concept of variables To be able to develop algorithms through the process of top-down, stepwise refinement. – To be able to convert the algorithm to pseudocode and flowcharts © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

3 2. 1 Introduction • Before writing a program: – Have a thorough understanding of the problem – Carefully plan an approach for solving it – The program should be carifully designed • While writing a program: – Know what “building blocks” are available – Use good programming principles © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

4 2. 2 Algorithms • Computing problems – All can be solved by executing a series of actions in a specific order • Algorithm: procedure in terms of – Actions to be executed – The order in which these actions are to be executed • Program control – Specify order in which statements are to be executed © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

Dack of Cards • • • In a game - dack of cards each player pull a card at the top of the dack read the task written on it perform the task then pull the next card on the top of the dack © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

Example 2. 1 Registration • A real life example • Describe steps of registration to an universty • step by step description of how a new commer is to register to an universty © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

Example 2. 1. Registering to an University Algorithm • 1 Obtain required forms • 2 Fill out the forms • 3 Other required materials are prepaired – identification, diploms • 4 Registration fee is paid • 5 forms are submited to the relevent person • 6 if something is mising – goto step 2 • 7 Sign the agrement • 8 Registration is complete © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved. 7

8 Notice that • When each step is compleated – next step is passed • it is also possible to branch a previous or later step – in this example from step 6 to srep 2 • The action in each step may depend on a condition – in step 6 if everything is OK continue otherwise branch to step 2 • Each of these steps may consists of sub steps – ex: step 2 fill out forms: there may be three different forms – each of which may be a sub step of step 2 • 2 a : a from for registration office • 2 b : a form for university hospital • 2 c : a form for university library © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

9 Example 2. 2 Calculating area of a regtangle • • Calcuating area of a rectangle Algortihm: 1 - Start 2 - Get value of hight 3 - Get value of width 4 - Multiply hight by width to obtain area 5 - Display the resulting area to the screen 6 - Stop © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

10 Note • • Without performing steps 2 and 3 Step 4 can not be performed Similarly Without performing steps 4 Step 5 can not be performed But Steps 2 and 3 can be interchanged © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

11 Exercis 2. 1 • Pick up a real life situation that interest you • for example: – driveing a car – cooking egg or cake • Construct the algorithm to explain step by step description of the actions to someone who does not have any idea obout that situation © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

12 2. 3 Pseudocode • Pseudocode – Artificial, informal language that helps us develop programs – One step closer to programming languages – Similar to everyday English on one side and programming languages on the other side – Not actually executed on computers – Helps us “think out” a program before writing it • Easy to convert into a corresponding C program • Consists only of executable statements © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

13 Pseudocode for Example 2. 2 1 Start 2 a Display “Enter height of the rectange” 2 b Input heigth 3 a Display “Enter width of the rectange” 3 b Input width 4 Set area = height * width 5 Display “The area of the regtanle” , area 6 Stop or end © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

14 Note That • In the algorithm : in step 2 – Getting the height from the user • In the pseudocode – – first write a message to be displayed in the screen informing the user what to enter as an input Then let the user enter a real number and press ENTER key The number entered by the user is stored in the variable heigth • Similarly for getting width of the rectangle – in step 3 © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

15 • When the pseudocode is implemented in any programming languare such as Java, C# or Python • The user first see the message “Enter height of the rectange ” in the computers screen The user is expected to enter real number for the height end press ENTER key • The Input heigth statement – obtains the chacters entered by the user converts into a numerical variable named height to be used in subsequent steps of the pseudocode or program © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

16 Building Blocks • • • Input output transfer Calculations in between - processing Decision making Iteration Variables – Store data in memory – different types in different languages – İntegers, real, character, string. logical, , . . • Input: obtain a value from the user and store in a variable – enter a value for radius of a circle to compute its area – enter your name lastname id number – make a choice Yes/No to save or not © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

17 Variables – Store data in memory – different types in different languages – Integers, real, character, string, logical (true or false). . . • numerical variables – heigth, width, age, total. Sales, numer of children • Strings : – Name, last name, address, e-mail – “Bertan” , “Badur”, “badur@boun. edu. tr” – usually presented in quats “. . . ” © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

18 Variable in daily iife • what is your name? – stored in your memory as a string • what is your age or weight – you know the meaning of age or weight – stroded as an integer or real and changes over time • What is your GPA – you know wht GPA is but not yet has a value as a new studeent • What is your garbay score – – this does not make a sense to you no such think in your memory when asked you are supprised or hesitate to answer BUT A COMPUTER PRGRAM FAİLS © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

19 Outtput • Output: display the results of the problem – some variables • display area – constant messages • Display “welcome to Java” • Display “you failed to register” – expressions • Display pi*r 2 – or a mixture of them • Display “the area is: “, area – E. g. : displays when the value of area is 200 – the area is: 200 © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

20 Calculations - processing • • Calculations aritmetic and logical computations intermediate resulst are also in variables E. g. : – Set area = hight*width • area is the product of hight and width – E. g. : • Set value. Added. Tax = tax. Rate*base. Payment – E. g. : – Set total = total + new grade • add new grade to the total © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

21 2. 4 Control Structures • Sequential execution – Statements executed one after the other in the order written • Transfer of control – When the next statement executed is not the next one in sequence – Overuse of goto statements led to many problems • Bohm and Jacopini – All programs written in terms of 3 control structures • Sequence structures: Built into Java. Programs executed sequentially by default • Selection structures: Java has three types: if, if…else, and switch • Repetition structures: Java has three types: while, do…while and for © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

22 Simple Building Blocks • We will start with – input • get data from the user • store in variables – process or calculation • Store the results in (new) variables – output • dsiplay message and/or variables to the screen • Variables of different types – Stored in memory – Referen by a name in our pseudocodes, and programs © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

23 2. 3 Flowcharts • Flowchart – Graphical representation of an algorithm – Drawn using certain special-purpose symbols connected by arrows called flowlines – Rectangle symbol (action symbol): • Indicates any type of action – Oval symbol: • Indicates the beginning or end of a program or a section of code • Single-entry/single-exit control structures – Connect exit point of one control structure to entry point of the next (control-structure stacking) – Makes programs easy to build © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

24 Flowchart Symbols start or end calculation flow decision making output input © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

25 Example 2. 3 Foreign Exchange Problem • The amount of $ in your hand makes how meny TL • 1 $ 6. 20 TL • Inputs: : – amount of dollar in your hand • Output: – How much does the dollar worth in terms of TL • : Limitations – 1 dolar is 6. 20 TL forex rate is constant – just convert to TL © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

Ex 2. 3 Algorithm of exchange rate calculation • • 1 Start 2 Define the forex rate 3 Get dollar amount 4 TL correspondence of the dollar is computed – TL = dollar * exchage rate • 5 dsiplay TL • 6 Stop or End • What variables are needed? – dollar, TL – exchange rate? © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved. 26

27 Pseudocode • • 1 Start 2 Set forex. Rate = 6. 20 3 a Display “Enter dollar in your hand” 3 b Input dollar 4 Set tl = dollar * forex. Rate 5 Display “your”, dollar , “worths”, tl 6 Stop or End © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

28 Variables • Forex. Rate – a real number set at the begining – fixed it does not change • dollar – dollar in the hand of the user – real input – every run of the program has a different value • tl – calculated TL amout for the dollar with the dixed forex. Rate © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

29 Limitations and Extensions • Limitations: – every time a new $ is given the algorithme start from begining – if the user enters a negative value it prints a negative NTL – if the user enters a character it fails to compute • Note: – should the exchange rate be asekd as a second input or is it fixed As it is not chaning very often but it may change hourly – Exercise: – Modify the algorithm when the for ex rate change as well • Extension of the problem – given NTL the user mey want to chose the forex ohter then dollar to purchase © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

30 Ex 2. 4. Length conversion • What is the equivanent of a given inch in term of cm • Inputs: – inch • Output: : – cm • Limitations: – just between inch and cm • Note: relation between c. m. and inch is constant and 1 inch is 2. 54 cm © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

31 Ex 2. 5. Area and circunference of circle • Given a radius of a circle calcualte its area and circunference • Inputs: – radius • Output: – area and circkunference – Note has two outputs • Limitations: – only for circle • Note: Pi is a universal constant as well 3. 14159 © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

32 Area and Circunference of circle • • 1 Start 2 Set the value of pi = 3. 1416 2 Get radius 4 Compute area and circunference 4. a area = pi * (radius)2 4 b circunf. = 2 * pi * radius 5 display area and circunference to the screen 6 Stop or end • What are variables? – radius, area, circunference • What about pi – its value does not change – universan constant • What are the limitations of the algorithm? © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

33 Pseudocode for Cirlcle • • 1 Start 2 Set pi = 3. 14 3 a Display “Enter radius” 3 b Input radius 4 a Set area = pi * radius 2 4 b Set circunference = 2 * pi * radius 5 a Display “Area of the circle is” , area 5 b Display “Circunference of the circle is”, circunference • 6 Stop © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

34 Ex 2. 7 Display a Fixed message • Display your signiture to the screen • when run always displays your name, last name, address and e-mail to the screen • Limitation: only one signiture for you • No input, no variables • Output Name: Bertan Last name: Badur Address: Bogazici University E-male: badur@boun. edu. tr © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

Ex 2. 8 Asking and displaying your personal information • Task: ask name lastname and age • dispay to the screeen • Inputs : name, last. Name – String • age - integer • Output: A messge that change according to your name last name and age but has some fixed characters • Example output • Name: İrem Last Name : Badur Age: 12& Associates, Inc. and Pearson Education Inc. All Rights Reserved. © • Copyright 1992– 2004 by Deitel 35

36 Algorithm • 1 Start • 2 Ask and get name, last name and age of a person • 2 a ask and get neme • 2 b ask and get last name • 2 c ask and get age • 3 Dispay personal information in a forfmated way to the screen • 3 a dispay name • 3 b dispay last name • 3 c dispay age • 4 Stop © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

37 Pseudocode • • • 1 Start 2 a i Display “Enter your name” 2 a ii Input name 2 b i Display “Enter your last name” 2 b ii Input last. Name 2 c i Display “Enter your age” 2 c ii Input age 3 a Display “Name: ” , name 3 b Display “Last Name: ”, last. Name 3 c Display “Age: ”, age 4 Stop © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

38 Variables • name , last. Name – String – set of characters • age – integer your age © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

39 Flowchart • Draw the flowchart © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

40 Ex 2. 9. Exam grades • Computes exam statistics • Inputs: – student grades • Outputs: – avgerage, min, max, letter grades, . . . • Limits: – only for one exam © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

A Simple Grade Average Calculation Problem • Task: There are only three students in a class • Ali, Ahmet and Nazlı. Get their exam grades from the user and calculate and display the class average to the screen. © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

42 Algorithm • A class consisting of three students: Ali, Ahmet, Nazlı 1 Start 2 Get Ali’s grade 3 Get Ahmet’s grade 4 Get Nazlı’s grade 5 Compute the average grade Average grade = (Ali’s grade + Ahmet’s grade + Nazlı’s grade)/3 6 Display the average grade 7 End • Variables: – Ali’s grade, Ahmet’s grade, Nazlı’s grade, – average grade © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

Pseudocode and variables 1 Start 2 a Declare Integer alis. Grade 2 b Declare Integer ahmets. Grade 2 c Declare Integer nazlis. Grade 2 d Declare Real average 3 a Display “Enter Ali’s grade” 3 b Input alis. Grade 4 a Display “Enter Ahmet’s grade” 4 b Input ahmets. Grade 5 a Display “Enter Nazli’s grade” 5 b Input nazlis. Grade © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

Pseudocode and variables (cont. ) 6 Set average = (alis. Grade + ahmets. Grade + nazlis. Grade)/3 7 Display “the class average” , average 8 End Variables alis. Grade, ahmets. Grede and nazlis. Grade are declared as integers average is declared as Real Note that: if this pseudocode is implemented in Java or C programming languages sum of three integers is an integer dividing by 3 you may lose the remainder because of ineger division © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

Solution • Declare the student grades as Real variables average = ( 10. 0 + 9. 0) / 3 here average is 9. 33333 • if grades are declared as integers average = (10 + 9) / 3 here average is 9. 00000 © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

Another Important feature • In step 6 of the pseudocode • average can be computed in one asignment statement • or it can be computed is steps as follows 6 a Set sum = alis. Grade 6 b Set sum = sum + ahmets. Grade 6 c Set sum = sum + nazlis. Grade 6 d average = sum / 3 How do you get rid of the information lose due to integer division ? © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

47 Ex 2. 10. Purchase • what is total payment after a sale • Inputs: – products SKU and amounts • Outut: – invoice total payment value added tax • Note prices of goods are not inputs © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

48 Purchase Problem tasl • two products apple and pair – prices are given not chaning • Value added tax – tax rate is constant • Input: – Amout. Apple, Amount. Pair – asked to user • Output: – net. Pay, VAT, gross. Pay – calculated and printed • Variables: – – Price. Apple, Price. Pair – fixed Amout. Apple, Amount. Pair – asked to user VAT Rate – fixed net. Pay, VAT, gross. Pay – calculated and printed © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

49 Purchase Problem Algorithm • 1 Start • 2 a define prices for the two goods – Price. Apple = 4, Price. Pair = 5 • 2 b define value added tax rate – VATRate = 0. 18 • 3 get amount of apple and pair purchased from the user • 4 Calculate net payment – net. Pay = Price. Apple*Amount. Apple + Price. Pair*Amount. Pair • 5 Calculate VAT – VAT ? net. Pay*VATRate • 6 Calculate gross payment – gross. Pay = net. Pay + VAT • 7 print net psyment, VATand total payment to screen • 8 End © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

50 pseudocode flowchart • Exercise to you • Note if you are sure that value of a variable will not change through out the program, • you can declare them a constants • many programming languages including Java has a syntax for constants • any attempt to change the value of a constant is a syntax error • Examples of well known constants pi = 3. 1416, e = 2. 713 speed of light, Avagadro number © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

Constants in pseudocodes • Constant Integer price. Apple = 4 • Constant Real pi = 3. 14 © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

52 Notes Purchase Problem • Note that • calculating net Paymnet can be performed in two steps as – 4 a Set net. Pay = Price. Apple*Amount. Apple – 4 b Set net. Pay = net. Pay + Price. Pair*Amount. Pair © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

53 Ex 2. 11. Tax Calculation • Compute the tax burden • Inputs: – yearly income • Output: – tax burden • Note: tax rate is given © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

54 Ex. 2. 12 Interest calculation • Depositing some money calculate interest earned on that • Inputs: – Principle – term – yearly interest rate • Output: – money – interest earned : © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

55 Exercise • Suppose a language does not support mode • In Java mode is implemented by % – 14 % 3 = 2 – 12 % 3 = 0 • How do you imlement mode if it is not supported by the language syntax © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

56 Solution • Mode opperation give the remainder • Ex 10 mode 3 = 1 • 9 mode 3 = 0 • Suppose mode is not supported by the syntax of a programming labnguage • How would you imlement mode? • Set modeab = a mode b • Set modeab = a – (a / b) * b • E. g. : if a = 8, b = 3 a mode b = 8 node 3 = 2 a – (a / b) * b = 8 – (8 / 3) * 3 = 8 – 2*3 = 2 © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

Ex 2. 13 ATM Problem • Consider a customer intending to withdraw money from an ATM, enters the amount she wnnt to withdrow • available types of notes are say: – 100, 50, 20, 10. . . – assume ATM pays as much 100 as possible then pays the remaining with 50 s and so on • Write the algorithm of money withdrawing problem. How much of the money is paid with what type of notes • and remainging money that can not be paid at all • E. g. : 643 TL is paid with • 6 100 s, 0 50 s, 2 20 s and 3 TL can not be paid © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

ATM Problem Hint • Hint: at each step try to identify how much of the money is paid with say by 100 s and what is the remaining amount © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

59 ATM Input and outputs • Input: – money from the user • Output: – – how many 100 TL how many 50 TL how many 20 TL how much not paid © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

60 ATM: Algorithm • • • 1 Start 2 Get money from the user 3 a Determine how many 100 s are paid 3 b Determine remaining money not paid by 100 s 4 a Determine how many 50 s are paid 4 b Determine remaining not paid by 50 s 5 a Determine how many 20 s are paid 5 b Determine how remaining not paid by 20 s 6 Determine money that can not be paid at all 7 Display the results 8 End © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

61 ATM: variables • Variables – input - money – output - how. Many 100, how. Many 50, how. Many 20, not. Paid – remaining - used for intermediate calculations © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

62 Pseudocode of Step 3 a and 3 b • 3 a determine how many 100 s are paid • 3 b determine remaining money not paid by 100 s – remaining = money – 3 a how. Many 100 = remaining / 100 – 3 b remaining = remaining mode 100 • • Example suppose money is 455 remaining = money: remaining becomes 455 how. Many 100 = 455 / 100 = 4 – integer division remaining = remaining mode 100 – remaining becomes 55 © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

63 Exercise • Complete the pseudocode • Draw the flowchart • Write the Java program © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

64 Exercise Time expression 1 • Given a duration of time in hours, munite and seconds expres it in total seconds • E. g. : given 2 hours, 3 minutes and 5 seconds it is 7385 seconds given 2 hours, 0 munites and 30 seconds it is 7230 seconds given 0 hours, 20 munites and 40 seconds it is 1240 seconds © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

65 Exercise: Time expresion 2 Given a duration of time in seconds Expres it in hours, munite and seconds E. g. : given 7385 seconds it is: 2 hours, 3 minutes and 5 seconds given 7230 seconds it is 2 hours, 0 munites and 30 seconds given 1240 seconds it is 0 hours, 20 munites and 40 seconds © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

66 Exercise: Exchange of values of variables • • Given two int type variables a, b hodling values E. g. : a = 5, b = 10 Change their values At the end of the change a becomes 10 , b becomes 5 i) By using a temporary variable İi) Without using a temporary variable © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

67 Exercise: Reverse of an Integer • Given a three digit integer – Examples: 174, 810, 400, 956 • print it in reverse order – Examples 174 to 471, 956 to 659, 400 to 4, 810 to 18 • Hint: : try to get its first digit, second digit and third digit • then try to construct the reverse number © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

68 Input and output • Input: – a three digit integer from the user • Output: – its reverse © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

69 Algorithm 1 • • • 1 Start 2 get number from user 3 determine ones 4 determine tens 5 determine hundrends 6 compute reverse as – reverse = 100*ones+10*tens+hundreds • 7 Display reverse to the screen • 8 End © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

70 Variables for Algorithm 1 • Variables – number– input from user – reverse – output to screen – ones, tens, hundreds, remaining © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

71 Hard of the Algorithm 1 • Set remaining = number // take a copy of number • 3 determine ones: 3 a Set ones = remaining mode 10 3 b Set remaining = remaining / 10 • Example: – – number is 743 remaing is 743 ones is 743 mode 10 = 3 remaining is 743 / 10 74 • perform step 4 amd 5 to find tens and hudereds © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

72 Algorithm 2 • • • 1 Start 2 get number from user 3 determine hundrends 4 determine tens 5 determine ones 6 compute reverse as – invnumber = 100*hundreds+10*tens+ones • 7 Display reverse • 8 end © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

73 Algorithm 2 • Set remaining = number // copy of money • 3 determine hundreds: 3 a Set hundreds = remaining / 100 3 b Set remaining = remaining mode 100 • Example: – – number is 743 remaing is 743 hundreds is 743 / 100 = 7 remaining is 743 mode 100 = 43 • perform step 4 amd 5 to find tens and ones © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

74 Algorithm 3 • • • 1 Start 2 initialize reverse to zero 3 get number from user 4 a determine ones 4 b update remainder 4 c update reverse 5 a determine tens 5 b update remainder 5 c update reverse © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

75 Algorithm 3 (contg. ) • • • 6 a determine hundrends 6 b update remainder 6 c update reverse 7 print reverse 8 end © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

76 Hard of Algorithm 3 • • initially reverse variable is set to 0 4 a determine ones: Set ones = remaining mode 10 4 b update remainder Set remaining = remaining / 10 4 c updata reverse Set reverse = 10*reverse + ones // inverse becomes ones © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

77 Hard of Algorithm 3 • • just before 5 inverse is ones 5 a determine tens: Set tens = remaining mode 10 5 b update remainder Set remaining = remaining / 10 5 c updata reverse Set reverse = 10*reverse + tems // inverse becomes left digit: onces, right digit: tens © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.