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Programming Principles II

Andreas Savva. Programming Principles II. Lecture Notes 1 Data Structures. 2 people. 14 people. 6 people. 10 people. 8 people. 3 people. Wagon :. [ 0 ]. [ 1 ]. [ 2 ]. [ 3 ]. [ 4 ]. [ 5 ]. Arrays. Wagon [ 0 ] = 2, Wagon [ 1 ] = 14, Wagon [ 4 ] = 8.

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Programming Principles II

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  1. Andreas Savva Programming Principles II Lecture Notes 1 Data Structures

  2. 2 people 14 people 6 people 10 people 8 people 3 people Wagon: [0] [1] [2] [3] [4] [5] Arrays Wagon[0] = 2, Wagon[1] = 14, Wagon[4] = 8

  3. How will you send me a letter? What will you write on the envelop? Eleftherias[1] Eleftherias[2] Eleftherias[3] 1 2 Eleftherias[7] 3 4 5 My House 6 7 8 Great Alexander Avenue Andreas Savva Eleftherias 4 Nicosia Eleftherias street

  4. 5th Floor Akropoli[5] Lift 5 4th Floor Akropoli[4] 4 3rd Floor Akropoli[3] 3 2 2nd Floor Akropoli[2] 1 0 1st Floor Akropoli[1] Ground Floor 0th Floor Akropoli[0] AKROPOLI BuildingAKROPOLI In C++ there are no basements

  5. Numbers[0] Numbers[1] Numbers[2] Numbers[3] Numbers[4] What is an Array (Table) • It is a set of sequential memory positions, that values of the same data-type are stored. • Every item in the table is called an element and it is specified by its position. • All the elements of the array have a common name (the name of the array) but have a different position. • It is NOT possible in C/C++ to define arrays with arbitrary starting and ending indexes.

  6. Table Name Values Example of a Table (Array) Numbers[0]  6 Numbers[1]  7 Numbers[2]  9 Numbers[3]  0 Numbers[4]  7

  7. Arrays <DataType> <Identifier>[<Dimension>]; Array positions: 0 to Dimension – 1 Example: int Numbers[10]; Positions: 0 to 9

  8. Example int DaysInMonth[12]; char SemesterGrade[5]; • DaysInMonth[4]  31 • SemesterGrade[2]  ’A’

  9. Example: #include <iostream> using namespace std; void main() { intΝ1[5], N2[5]; N1[2] = 4; N1[0] = N1[2]; N2[4] = N1[0]; } Accessing the Array 4 4 4

  10. VAR boolA[100]; intB[9]; intC[1000]; doubleD[6]; char E[10]; Array Declaration Examples

  11. Output: 27 29 31 33 35 16 17 18 19 20 Arrays and For-loops #include <iostream> using namespace std; constint MAX = 10; void main() { int A[MAX], i; for (i = 0; i < MAX; i++) A[i] = i + 11; for (i = 0; i < MAX / 2; i++) A[i] += A[i+5]; for (i = 0; i < MAX; i++) cout << A[i] << endl; }

  12. Array Bounds • What happens if we try and access an element beyond the bounds of the array? max = A[370]; • or, even worse, write to it? A[-10] = 32; • Answer: • Nothing! • The program will compile • It may cause runtime errors • It may cause serious problems (during testing if lucky)

  13. Some Important Array Operations for (i = 0; i < MAX; i++) A[i] = B[i]; or copying in reverse for (i = 0; i < MAX; i++) A[MAX-1-i] = B[i]; Copying an array: for ( i = 0; i < MAX; i++) A[i] = 0; or for (i = 0; i < MAX; i++) Symbol[i] = ’ ’; Initializing: for (i = 0; i < MAX; i++) cin >> A[i]; Reading: for (i = 0; i < MAX; i++) cout << A[i]; Writing:

  14. Some Important Array Operations Sum = 0; for (i = 0; i < MAX; i++) Sum += A[i]; cout << ”The sum is ” << Sum; Summing: i = 0; Found = false; while (!Found && (i < MAX)) Found = A[i++] == SearchingKey; if (Found) cout << SearchingKey << ” is found”; else cout <<SearchingKey << ” is not found”; Searching:

  15. Two-Dimensional ArraysTables Sales per month for three types of cars for the year 2005

  16. Referencing a Flat: Akropoli[Floor][FlatNo] Akropoli[4][03] Akropoli[2][02] Akropoli[2][01] Akropoli[0][02] 401 301 101 201 402 102 202 302 203 103 303 403 001 002 003 BuildingAKROPOLI

  17. Two-Dimensional Arrays • Declaring the Array (12 rows, 3 columns) int sales[12][3]; • Referencing the Array (Make the sales of Renault for March be 11) sales[2][1] = 11; • Remember: indexes start at 0

  18. 2D Arrays Example Addition of Matrices: #include <iostream> using namespace std; void main(){ float M1[2][3],M2[2][3],Result[2][3]; int row, col; for (row=0; row<2; row++) // Read matrix 1 for (col=0; col<3; col++) cin >> M1[row][col]; for (row=0; row<2; row++) // Read matrix 2 for (col=0; col<3; col++) cin >> M2[row][col]; for (row=0; row<2; row++) // Add the two matrices for (col=0; col<3; col++) Result[row][col]= M1[row][col] + M2[row][col]; for (row=0; row<2; row++) { // Display the result for (col=0; col<3; col++) cout << Result[row][col] << ’\t’; cout << endl; } }

  19. x, y, z double picture[MAX][MAX][3]; z y x Multi-Dimensional Arrays picture

  20. Array Initialization • Arrays can be initialized at definition like normal variables. • Single-dimensional arrays • Array of 5, all elements initialized float prices[5]={1.25, 3.50, 1.20, 2.99, 0.75}; • Array of 5, the first two elements initialized float prices[5]={1.25, 3.50}; • Array whose length is determined by initialization int months[ ]={1,2,3,4,5,6,7,8,9,10,11,12}; • Multi-dimensional arrays • Matrices 3x2, all elements initialized int x[2][3]={1,2,3,3,2,1}; // either like this... int y[2][3]={{1,2,3},{3,2,1}}; // ...or like this

  21. Constant Arrays const int Fibonacci[] = {1, 1, 2, 3, 5, 8, 13, 21}; Fibonacci cannot be changed. Thus the following will give a syntax error. Fibonacci[2] = 5; 

  22. Declaring Arrays const int MAX_GRADES = 100; … int grades[MAX_GRADES]; const int MAX_ROWS = 8; const int MAX_COLS = 4; … int table[MAX_ROWS][MAX_COLS];

  23. Strings • C++ has two ways of storing and manipulating strings: • Using the string class • C-Strings – array of characters • Reasons for using a stringclass object: • It does a bounds check on every index used to access string elements. This is not true for C-strings, and using an invalid C-string index can result in system crash. • It expands and constructs storage as needed. C-strings are fixed in length and are subject to overrunning the allocation storage space. • It provides a rich set of methods for operating on a string. C-strings almost always require a subsidiary set of functions. • When necessary, it is easy to convert to C-strings using the method c_str(). Also a C-string can be assigned to a string object. • Reasons for using a C-string: • The programmer has ultimate control over how the string is stored and manipulated. • A large number of useful functions exist to input, examine and process C-strings. • They are an excellent way to explore advance programming techniques using pointers. • You will encounter them throughout your programming career, as they are embedded in almost all existing C++ code. • They are fun to program.

  24. String – Array of Characters • The last character in the string is the NULL character, ’\0’. • ’\0’must be present for the string to be valid! Example: char message[6]={’H’,’e’,’l’,’l’,’o’,’\0’}; • You must remember to leave extra space to store the NULL character, otherwise results could be unpredictable.

  25. CY Strings • C/C++ provide a shorthand for initializing and defining strings, using double quotes (”...”) to enclose the string. In this case the NULL is added automatically. char message[6]=”Hello”; • Strings start at position zero and terminated at the first NULL character. cout << Word;

  26. Hello World Yellow Example #include <iostream> using namespace std; void main(){ char message[20] = ”Hello World”; cout << message << endl; message[0] = ’Y’; message[5] = ’w’; message[6] = ’\0’; cout << message << endl; } ’w’ ’Y’ ’\0’

  27. message ”What” message ”What a nice day!” Reading a String The command cin >> message; will read a string until the first control character. Thus if the input is: What a nice day! then message will have the value ”What”. We can use the function gets(message) to read the whole line into message (Library: <stdio.h>).

  28. Reading a Character The command cin >> c; will read only non-control characters. Thus if the input is: What a nice day! the statement while(cin >> c, c!=’!’) cout << c; will display Whataniceday. We can use the function cin.get() that reads any character (including control characters). Therefore the statement while(c=cin.get(), c!=’!’) cout << c; will display What a nice day

  29. Reading a String We can also read a line of string with the following code: #include <iostream> using namespace std; void main() { char c, message[255]; int i=0; while (c=cin.get(), i<254 && c!=’\n’) message[i++] = c; message[i] = ’\0’; cout << message << endl; }

  30. Type a line of text and press <enter> I am a student tneduts a ma I Example // Reads in a line of text and prints it in reverse order #include <iostream.h> #include <stdio.h> #define MAXLEN 256 // max length of strings used void main() { char inline[MAXLEN], outline[MAXLEN]; int i,j; cout << ”Type a line of text and press <enter>\n”; gets(inline); for (i=0;inline[i]!=’\0’;i++) ; // find end of string for (j=0,i--;i>=0;j++,i--) outline[j]=inline[i]; outline[j]=’\0’; //terminate string cout << outline << ’\n’; // print text in reverse }

  31. String Functions • There are a number of ready to use string-related operations (functions). • These are accessible by including the definitions from the header file <cstring> in your program. • Among them you get: strlen(s) returns the length of string s strcpy(s2,s1) copies a string s1 to another string s2 strcat(s2,s1) concatenates s1 at the end of s2 strcmp(s2,s1) compares s1 and s2, returns 0 if equal

  32. strlen(s) Function Length – Returns the size of the string strlen(String)  integer i.e. strlen(”I like school”)  13 strlen(”123456789:?@”)  12 Counting how many times character ’A’ is in the string Name: int i, Count = 0; char Name[100]; . . . for (i = 0; i < strlen(Name); i++) if (Name[i] == ’A’) Count++; cout << ”Character -A- found ” << Count << ” times”;

  33. s1 s2 ”one” ”one” strcpy(s1,s2) strcpy(<StringVariable>, <StringValue>); char s1[20] = ”Thirty ”, s2[20] = ”one”; strcpy(s1,s2); char s1[20] = ”Thirty ”; s2[20] = ”one”; strcpy(s1,”one”); Errors: strcpy(”one”,s1); s1 = s2;

  34. s2 s1 ”Thirty one” ”one” strcat(s1,s2) strcat(<StringVariable>, <StringValue>); char s1[20] = ”Thirty ”, s2[20] = ”one”; strcat(s1,s2); char s1[20] = ”Thirty ”; s2[20] = ”one”; strcat(s1,”one”); Error: strcat(”one”,s1);

  35. C++ strcmp(<String1>, <String2>)  integer; If String1 > String2 it will return an integer > 0 If String1 == String2 it will return 0 If String1 < String2 it will return an integer < 0 strcmp(s1,s2) = true = false = false Comparing Strings? (This is not C++) • ”George” < ”Mark” • ”George” = ”george” • ”Plant” < ”Planet” ’t’ > ’e’

  36. Converting String to Integer • Library: <stdlib.h> • Example: int x = atoi(”342”); // x = 342 int x = atoi(”342Hello856”); // x = 342 atoi(String)  Integer

  37. 13 - 13 1110101011 1110101011 1b – 1b Converting Integer to String • Library: <stdlib.h> • Example: char s[10]; cout << itoa(13, s, 10) << ” – ” << s; cout << itoa(0x3Ab, s, 2) << endl << s; cout << itoa(27, s, 16) << ” – ” << s; itoa(int, char *, int)  String Number to convert Base Returning string

  38. h ? B clint eastwood Character Functions • Library: <stdlib.h> • Example: cout << tolower(’H’) << ’\n’; cout << tolower(’?’) << ’\n’; cout << toupper(’b’) >> ’\n’; char s[] = ”Clint Eastwood”; for (inti=0; i < strlen(s); i++) cout << tolower(s[i]); tolower(char)  char toupper(char)  char

  39. Character Functions islower(char)  bool • Examples: islower(’H’) = false islower(’h’) = true islower(’?’) = false isupper(’H’) = true isupper(char)  bool

  40. Syntax: enum <type name> {<value1>,<value2>, … ,<valueΝ>}; Examples: enum Day{Mon, Tue, Wed, Thu, Fri, Sat, Sun}; enum Season {Winter, Spring, Summer, Autumn}; enumColour {Red, Green, Blue}; enumGrade {A, B, C, D, F}; enumMyBoolean {MyFalse, MyTrue}; Enumerated Types • The user can declare a new data-type in which he can also define its values.

  41. 0 1 2 3 4 5 6 Example: enum Day{Mon, Tue, Wed, Thu, Fri, Sat, Sun}; Day d; Enumerated Data Types  d = Fri; d = ”Fri”; d = Friday; d = 4; d = d++; Mon < Tue Tue < Wed int(Mon) = 0 int(Fri) = 4 (Day)(Thu+1) = Fri (Day)(Tue-1) = Mon    

  42. Enumerated Data Types • Can be used as any other data type, e.g. if (d <= Fri) cout << ”Weekday”; else cout << ”Weekend”; for (d=Mon; d<=Sun; d=(Day)(d+1)) ...

  43. Enumerated Data Types  • Cannot read enumerated type values. • cin >> d; // will give a syntax error • cout << d; // will display its ordinal position switch (d) { case Mon : cout << ”Monday”; break; case Tue : cout << ”Tuesday”; break; case Wed : cout << ”Wednesday”; break; case Thu : cout << ”Thursday”; break; case Fri : cout << ”Friday”; break; case Sat : cout << ”Saturday”; break; case Sun : cout << ”Sunday”; break; default : break; } Outputtingthe day

  44. Why the following declaration is wrong? enum Grade {1,2,3,4,5,6,7,8,9,10}; Exercise #include <iostream> using namespace std; void main() { enum Grade {A,B,C,D,F}; Grade exam; for (exam=A; exam<=F; exam=(Grade)(exam+1)) switch (exam) { case A : cout << ”Excellent\n”; break; case B : cout << ”Very Good\n”; break; case C : cout << ”Good\n”; break; case D : cout << ”Pass\n”; break; default: break; } } • What is the output of the following program?

  45. 1 2 3 1 2 3 4 5 6 7 0 1 2 1 2 Enumeration enum Color {Red=1, Green=2, Blue=3}; enum Day{Mon=1, Tue, Wed, Thu, Fri, Sat, Sun}; enum Month {Jan=1, Feb=1, Mar=2, Apr=2, May=2, Jun=3, Jul=3, Aug=3, Sep=4, Oct=4, Nov=4, Dec=1}; enum Rainbow {Red, Orange, Yellow, Green=1, Blue};

  46. Enumerated Types in Arrays enum Season {Winter, Spring, Summer, Autumn}; enum Day{Mon, Tue, Wed, Thu, Fri, Sat, Sun}; enum Color {Red, Green, Blue}; Day A[5]; Color B[8]; Season C[4];

  47. Programming Example #include <iostream> using namespace std; void main() { enum Day {Mon,Tue,Wed,Thu,Fri,Sat,Sun}; float hours[7], salary=0.0; cout << ”Enter working hours from Monday to Sunday\n”; for (Day d=Mon; d<=Sun; d=(Day)(d+1)) cin >> hours[d]; for (d=Mon; d<=Sun; d=(Day)(d+1)) if (d==Sat || d==Sun) salary += hours[d] * 2.0; else salary += hours[d] * 1.5; cout << ”Your salary is ” << salary; }

  48. Arrays vs Records • Array • Sequence of elements (data types) • Position association among the elements • Record • Collection of data into a single structure • No association

  49. Records • Records in C++ are called structures (struct) or classes (class). Date struct date { char strDay[4]; int day; int month; int year; }; class date { public: char strDay[4]; int day; int month; int year; };

  50. today ”Mon” 28 3 2006 Structures class date { public: char strDay[4]; int day; int month; int year; }; date today; • Data members are accessed as: • today.strDay • today.day • today.month • today.year strcpy(today.strDay,”Mon”); today.day = 28; today.month = 3; today.year = 2006;

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