Chapter 2. C++ Basics. Copyright 2015 Pearson Education, Ltd.. All rights reserved.

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5 Variables ad Assigmets Variables are like small blackboards We ca write a umber o them We ca chage the umber We ca erase the umber C++ variables are ames for memory locatios We ca write a value i them We ca chage the value stored there We caot erase the memory locatio Some value is always there Display 2.1 Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-5

6 Idetifiers Variables ames are called idetifiers Choosig variable ames Use meaigful ames that represet data to be stored First character must be a letter the uderscore character Remaiig characters must be letters umbers uderscore character Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-6

7 Keywords Keywords (also called reserved words) Are used by the C++ laguage Must be used as they are defied i the programmig laguage Caot be used as idetifiers Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-7

8 Declarig Variables (Part 1) Before use, variables must be declared Tells the compiler the type of data to store Examples: it umber_of_bars; double oe_weight, total_weight; it is a abbreviatio for iteger. could store 3, 102, 3211, -456, etc. umber_of_bars is of type iteger double represets umbers with a fractioal compoet could store 1.34, 4.0, , etc. oe_weight ad total_weight are both of type double Copyright 2015 Pearso Educatio, Ltd.. All rights reserved.

9 Declarig Variables (Part 2) Immediately prior to use Two locatios for variable declaratios it mai() { it sum; sum = score1 + score 2; retur 0; } At the begiig it mai() { it sum; sum = score1 + score2; retur 0; } Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-9

10 Declarig Variables (Part 3) Declaratio sytax: Type_ame Variable_1, Variable_2,... ; Declaratio Examples: double average, m_score, total_score; double moo_distace; it age, um_studets; it cars_waitig; Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-10

11 Assigmet Statemets A assigmet statemet chages the value of a variable total_weight = oe_weight + umber_of_bars; total_weight is set to the sum oe_weight + umber_of_bars Assigmet statemets ed with a semi-colo The sigle variable to be chaged is always o the left of the assigmet operator = O the right of the assigmet operator ca be Costats -- age = 21; Variables -- my_cost = your_cost; Expressios -- circumferece = diameter * ; Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-11

12 Assigmet Statemets ad Algebra The = operator i C++ is ot a equal sig The followig statemet caot be true i algebra umber_of_bars = umber_of_bars + 3; I C++ it meas the ew value of umber_of_bars is the previous value of umber_of_bars plus 3 Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-12

13 Iitializig Variables Declarig a variable does ot give it a value Givig a variable its first value is iitializig the variable Variables are iitialized i assigmet statemets double mpg; // declare the variable mpg = 26.3; // iitialize the variable Declaratio ad iitializatio ca be combied usig two methods Method 1 double mpg = 26.3, area = 0.0, volume; Method 2 double mpg(26.3), area(0.0), volume; Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-13

14 Sectio 2.1 Coclusio Ca you Declare ad iitialize two itegers variables to zero? The variables are amed feet ad iches. Declare ad iitialize two variables, oe it ad oe double? Both should be iitialized to the appropriate form of 5. Give good variable ames for idetifiers to store the speed of a automobile? a hourly pay rate? the highest score o a exam? Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-14

16 Iput ad Output A data stream is a sequece of data Typically i the form of characters or umbers A iput stream is data for the program to use Typically origiates at the keyboard at a file A output stream is the program s output Destiatio is typically the moitor a file Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-16

17 Output usig cout cout is a output stream sedig data to the moitor The isertio operator "<<" iserts data ito cout Example: cout << umber_of_bars << " cady bars\"; This lie seds two items to the moitor The value of umber_of_bars The quoted strig of characters " cady bars\" Notice the space before the c i cady The \ causes a ew lie to be started followig the s i bars A ew isertio operator is used for each item of output Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-17

18 Examples Usig cout This produces the same result as the previous sample cout << umber_of_bars ; cout << " cady bars\"; Here arithmetic is performed i the cout statemet cout << "Total cost is $" << (price + tax); Quoted strigs are eclosed i double quotes ("Walter") Do t use two sigle quotes (') A blak space ca also be iserted with cout << " " ; if there are o strigs i which a space is desired as i " cady bars\" Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-18

19 Iclude Directives Iclude Directives add library files to our programs To make the defiitios of the ci ad cout available to the program: #iclude <iostream> Usig Directives iclude a collectio of defied ames To make the ames ci ad cout available to our program: usig amespace std; Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-19

20 Escape Sequeces Escape sequeces tell the compiler to treat characters i a special way '\' is the escape character To create a ewlie i output use \ cout << "\"; or the ewer alterative cout << edl; Other escape sequeces: \t -- a tab \\ -- a backslash character \" -- a quote character Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-20

21 Formattig Real Numbers Real umbers (type double) produce a variety of outputs double price = 78.5; cout << "The price is $" << price << edl; The output could be ay of these: The price is $78.5 The price is $ The price is $ e01 The most ulikely output is: The price is $78.50 Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-21

22 Showig Decimal Places cout icludes tools to specify the output of type double To specify fixed poit otatio setf(ios::fixed) To specify that the decimal poit will always be show setf(ios::showpoit) To specify that two decimal places will always be show precisio(2) Example: cout.setf(ios::fixed); cout.setf(ios::showpoit); cout.precisio(2); cout << "The price is " << price << edl; Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-22

23 Iput Usig ci ci is a iput stream brigig data from the keyboard The extractio operator (>>) removes data to be used Example: cout << "Eter the umber of bars i a package\"; cout << " ad the weight i ouces of oe bar.\"; ci >> umber_of_bars; ci >> oe_weight; This code prompts the user to eter data the reads two data items from ci The first value read is stored i umber_of_bars The secod value read is stored i oe_weight Data is separated by spaces whe etered Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-23

24 Readig Data From ci Multiple data items are separated by spaces Data is ot read util the eter key is pressed Allows user to make correctios Example: ci >> v1 >> v2 >> v3; Requires three space separated values User might type <eter key> Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-24

25 Desigig Iput ad Output Prompt the user for iput that is desired cout statemets provide istructios cout << "Eter your age: "; ci >> age; Notice the absece of a ew lie before usig ci Echo the iput by displayig what was read Gives the user a chace to verify data cout << age << " was etered." << edl; Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-25

26 Sectio 2.2 Coclusio Ca you write a iput statemet to place a value i the variable the_umber? Write the output statemet to prompt for the value to store i the_umber? Write a output statemet that produces a ewlie? Format output of ratioal umbers to show 4 decimal places? Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-26

28 Data Types ad Expressios 2 ad 2.0 are ot the same umber A whole umber such as 2 is of type it A real umber such as 2.0 is of type double Numbers of type it are stored as exact values Numbers of type double may be stored as approximate values due to limitatios o umber of sigificat digits that ca be represeted Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-28

30 Writig Double Costats Type double ca be writte i two ways Simple form must iclude a decimal poit Examples: Floatig Poit Notatio (Scietific Notatio) Examples: 3.41e1 meas e17 meas e-6 meas Number left of e does ot require a decimal poit Expoet caot cotai a decimal poit Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-30

31 Other Number Types Various umber types have differet memory requiremets More precisio requires more bytes of memory Very large umbers require more bytes of memory Very small umbers require more bytes of memory Display 2.2 Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-31

32 Iteger types log or log it (ofte 4 bytes) Equivalet forms to declare very large itegers log big_total; log it big_total; short or short it (ofte 2 bytes) Equivalet forms to declare smaller itegers short small_total; short it small_total; Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-32

33 Floatig poit types log double (ofte 10 bytes) Declares floatig poit umbers with up to 19 sigificat digits log double big_umber; float (ofte 4 bytes) Declares floatig poit umbers with up to 7 sigificat digits float ot_so_big_umber; Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-33

34 Type char Computers process character data too char Short for character Ca be ay sigle character from the keyboard To declare a variable of type char: char letter; Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-34

35 char costats Character costats are eclosed i sigle quotes char letter = 'a'; Strigs of characters, eve if oly oe character is eclosed i double quotes "a" is a strig of characters cotaiig oe character 'a' is a value of type character Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-35

36 C++11 Types The size of umeric data types ca vary from oe machie to aother. For example, a it might be 32 bits or 64 bits C++11 itroduced ew iteger types that specify exactly the size ad whether or ot the data type is siged or usiged Display 2.3 C++11 also has a auto type that deduces the type of the variable based o the expressio o the right had side of the assigmet auto x = 2.4 * 10; // x becomes a double due to 2.4 Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-36

37 Readig Character Data ci skips blaks ad lie breaks lookig for data The followig reads two characters but skips ay space that might be betwee char symbol1, symbol2; ci >> symbol1 >> symbol2; User ormally separate data items by spaces J D Results are the same if the data is ot separated by spaces JD Display 2.4 Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-37

38 Type strig strig is a class, differet from the primitive data types discussed so far Differece is discussed i Chapter 8 Use double quotes aroud the text to store ito the strig variable Requires the followig be added to the top of your program: #iclude <strig> To declare a variable of type strig: Display 2.5 strig ame = "Apu Nahasapeemapetilo"; Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-38

39 Type Compatibilities I geeral store values i variables of the same type This is a type mismatch: it it_variable; it_variable = 2.99; If your compiler allows this, it_variable will most likely cotai the value 2, ot 2.99 Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-39

40 it ßà double (part 1) Variables of type double should ot be assiged to variables of type it it it_variable; double double_variable; double_variable = 2.00; it_variable = double_variable; If allowed, it_variable cotais 2, ot 2.00 Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-40

41 it ßà double (part 2) Iteger values ca ormally be stored i variables of type double double double_variable; double_variable = 2; double_variable will cotai 2.0 Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-41

42 char ß à it The followig actios are possible but geerally ot recommeded! It is possible to store char values i iteger variables it value = 'A'; value will cotai a iteger represetig 'A' It is possible to store it values i char variables char letter = 65; Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-42

43 bool ß à it The followig actios are possible but geerally ot recommeded! Values of type bool ca be assiged to it variables True is stored as 1 False is stored as 0 Values of type it ca be assiged to bool variables Ay o-zero iteger is stored as true Zero is stored as false Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-43

44 Arithmetic Arithmetic is performed with operators + for additio - for subtractio * for multiplicatio / for divisio Example: storig a product i the variable total_weight total_weight = oe_weight * umber_of_bars; Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-44

45 Results of Operators Arithmetic operators ca be used with ay umeric type A operad is a umber or variable used by the operator Result of a operator depeds o the types of operads If both operads are it, the result is it If oe or both operads are double, the result is double Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-45

46 Divisio of Doubles Divisio with at least oe operator of type double produces the expected results. double divisor, divided, quotiet; divisor = 3; divided = 5; quotiet = divided / divisor; quotiet = Result is the same if either divided or divisor is of type it Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-46

47 Divisio of Itegers Be careful with the divisio operator! it / it produces a iteger result (true for variables or umeric costats) it divided, divisor, quotiet; divided = 5; divisor = 3; quotiet = divided / divisor; The value of quotiet is 1, ot Iteger divisio does ot roud the result, the fractioal part is discarded! Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-47

48 Iteger Remaiders % operator gives the remaider from iteger divisio it divided, divisor, remaider; divided = 5; divisor = 3; remaider = divided % divisor; The value of remaider is 2 Display 2.6 Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-48

49 Arithmetic Expressios Use spacig to make expressios readable Which is easier to read? x+y*z or x + y * z Display 2.7 Precedece rules for operators are the same as used i your algebra classes Use paretheses to alter the order of operatios x + y * z ( y is multiplied by z first) (x + y) * z ( x ad y are added first) Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-49

50 Operator Shorthad Some expressios occur so ofte that C++ cotais to shorthad operators for them All arithmetic operators ca be used this way += cout = cout + 2; becomes cout += 2; *= bous = bous * 2; becomes bous *= 2; /= time = time / rush_factor; becomes time /= rush_factor; %= remaider = remaider % (ct1+ ct2); becomes remaider %= (ct1 + ct2); Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-50

53 Brach Example To calculate hourly wages there are two choices Regular time ( up to 40 hours) gross_pay = rate * hours; Overtime ( over 40 hours) gross_pay = rate * * rate * (hours - 40); The program must choose which of these expressios to use Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-53

54 Desigig the Brach Decide if (hours >40) is true If it is true, the use gross_pay = rate * * rate * (hours - 40); If it is ot true, the use gross_pay = rate * hours; Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-54

55 Implemetig the Brach if-else statemet is used i C++ to perform a brach if (hours > 40) gross_pay = rate * * rate * (hours - 40); else gross_pay = rate * hours; Display 2.8 Display 2.9 Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-55

56 Boolea Expressios Boolea expressios are expressios that are either true or false compariso operators such as '>' (greater tha) are used to compare variables ad/or umbers (hours > 40) Icludig the paretheses, is the boolea expressio from the wages example A few of the compariso operators that use two symbols (No spaces allowed betwee the symbols!) >= greater tha or equal to!= ot equal or iequality = = equal or equivalet Display 2.10 Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-56

57 if-else Flow Cotrol (1) if (boolea expressio) true statemet else false statemet Whe the boolea expressio is true Oly the true statemet is executed Whe the boolea expressio is false Oly the false statemet is executed Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-57

58 if-else Flow Cotrol (2) if (boolea expressio) { true statemets } else { false statemets } Whe the boolea expressio is true Oly the true statemets eclosed i { } are executed Whe the boolea expressio is false Oly the false statemets eclosed i { } are executed Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-58

59 AND Boolea expressios ca be combied ito more complex expressios with && -- The AND operator True if both expressios are true Sytax: (Compariso_1) && (Compariso_2) Example: if ( (2 < x) && (x < 7) ) True oly if x is betwee 2 ad 7 Iside paretheses are optioal but ehace meaig Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-59

60 OR -- The OR operator (o space!) True if either or both expressios are true Sytax: (Compariso_1) (Compariso_2) Example: if ( ( x = = 1) ( x = = y) ) True if x cotais 1 True if x cotais the same value as y True if both comparisos are true Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-60

61 NOT! -- egates ay boolea expressio!( x < y) True if x is NOT less tha y!(x = = y) True if x is NOT equal to y! Operator ca make expressios difficult to uderstad use oly whe appropriate Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-61

62 Iequalities Be careful traslatig iequalities to C++ if x < y < z traslates as if ( ( x < y ) && ( y < z ) ) NOT if ( x < y < z ) Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-62

63 Pitfall: Usig = or == ' = ' is the assigmet operator Used to assig values to variables Example: x = 3; '= = ' is the equality operator Used to compare values Example: if ( x == 3) The compiler will accept this error: if (x = 3) but stores 3 i x istead of comparig x ad 3 Sice the result is 3 (o-zero), the expressio is true Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-63

64 Compoud Statemets A compoud statemet is more tha oe statemet eclosed i { } Braches of if-else statemets ofte eed to execute more that oe statemet Example: if (boolea expressio) { true statemets } else { false statemets } Display 2.11 Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-64

65 Braches Coclusio Ca you Write a if-else statemet that outputs the word High if the value of the variable score is greater tha 100 ad Low if the value of score is at most 100? The variables are of type it. Write a if-else statemet that outputs the word Warig provided that either the value of the variable temperature is greater tha or equal to 100, or the of the variable pressure is greater tha or equal to 200, or both. Otherwise, the if_else sttemet outputs the word OK. The variables are of type it. Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-65

66 Simple Loops Whe a actio must be repeated, a loop is used C++ icludes several ways to create loops We start with the while-loop Example: while (cout_dow > 0) { cout << "Hello "; cout_dow -= 1; } Output: Hello Hello Hello whe cout_dow starts at 3 Display 2.12 Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-66

67 While Loop Operatio First, the boolea expressio is evaluated If false, the program skips to the lie followig the while loop If true, the body of the loop is executed Durig executio, some item from the boolea expressio is chaged After executig the loop body, the boolea expressio is checked agai repeatig the process util the expressio becomes false A while loop might ot execute at all if the boolea expressio is false o the first check Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-67

68 while Loop Sytax while (boolea expressio is true) { statemets to repeat } Semi-colos are used oly to ed the statemets withi the loop while (boolea expressio is true) statemet to repeat Display 2.13 Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-68

69 do-while loop A variatio of the while loop. A do-while loop is always executed at least oce The body of the loop is first executed The boolea expressio is checked after the body has bee executed Sytax: do { statemets to repeat Display 2.14 Display 2.15 } while (boolea_expressio); Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-69

70 Icremet/Decremet Uary operators require oly oe operad + i frot of a umber such as +5 - i frot of a umber such as icremet operator Adds 1 to the value of a variable x ++; is equivalet to x = x + 1; -- decremet operator Subtracts 1 from the value of a variable x --; is equivalet to x = x 1; Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-70

71 Sample Program Bak charge card balace of $50 2% per moth iterest How may moths without paymets before your balace exceeds $100 After 1 moth: $50 + 2% of $50 = $51 After 2 moths: $51 + 2% of $51 = $52.02 After 3 moths: $ % of $52.02 Display 2.16 Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-71

72 Ifiite Loops Loops that ever stop are ifiite loops The loop body should cotai a lie that will evetually cause the boolea expressio to become false Example: Prit the odd umbers less tha 12 x = 1; while (x!= 12) { cout << x << edl; x = x + 2; } Better to use this compariso: while ( x < 12) Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-72

73 Sectio 2.4 Coclusio Ca you Show the output of this code if x is of type it? x = 10; while ( x > 0) { cout << x << edl; x = x 3; } Show the output of the previous code usig the compariso x < 0 istead of x > 0? Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-73

76 Program Style - Idetig Items cosidered a group should look like a group Skip lies betwee logical groups of statemets Idet statemets withi statemets if (x = = 0) statemet; Braces {} create groups Idet withi braces to make the group clear Braces placed o separate lies are easier to locate Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-76

77 Program Style - Commets // is the symbol for a sigle lie commet Commets are explaatory otes for the programmer All text o the lie followig // is igored by the compiler Example: //calculate regular wages gross_pay = rate * hours; /* ad */ eclose multiple lie commets Example: /* This is a commet that spas multiple lies without a commet symbol o the middle lie */ Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-77

78 Program Style - Costats Number costats have o memoic value Number costats used throughout a program are difficult to fid ad chage whe eeded Costats Allow us to ame umber costats so they have meaig Allow us to chage all occurreces simply by chagig the value of the costat Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-78

79 Costats cost is the keyword to declare a costat Example: cost it WINDOW_COUNT = 10; declares a costat amed WINDOW_COUNT Its value caot be chaged by the program like a variable It is commo to ame costats with all capitals Display 2.17 Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-79

80 Sectio 2.5 Coclusio Ca you Create a amed costat of type double? Determie if a program ca modify the value of a costat? Describe the beefits of commets? Explai why idetig is importat i a program? Explai why blak lies are importat i a program? Copyright 2015 Pearso Educatio, Ltd.. All rights reserved. Slide 2-80

Chapter 2. C++ Basics

Chapter 2. C++ Basics Chapter 2 C++ Basics Overview 2.1 Variables and Assignments 2.2 Input and Output 2.3 Data Types and Expressions 2.4 Simple Flow of Control 2.5 Program Style Slide 2-2 2.1 Variables and Assignments Variables