1. Chapter 7: Arrays

2. Outline Array Definition Access Array Array Initialization Array Processing 2D Array

3. Slide 7- 3 Array Terminology The above definition allocates the following memory: first element second element third element fourth element fifth element

4. Slide 7- 4 Array Terminology The size of an array is: – the total number of bytes allocated for it – (number of elements) * (number of bytes for each element) Examples: int tests[5] is an array of 20 bytes, assuming 4 bytes for an int long double measures[10] is an array of 80 bytes, assuming 8 bytes for a long double

5. Slide 7- 5 Accessing Array Elements Each element in an array is assigned a unique subscript. Subscripts start at 0 The last element’s subscript is n-1 where n is the number of elements in the array. 01234 subscripts:

6. Slide 7- 6 Accessing Array Elements Array elements can be used as regular variables: tests[0] = 79; cout << tests[0]; cin >> tests[1]; tests[4] = tests[0] + tests[1]; Arrays must be accessed via individual elements: cout << tests; // not legal!!

7. Slide 7- 7 Using a Loop to Step Through an Array Example – The following code defines an array, numbers, and assigns 99 to each element: const int ARRAY_SIZE = 5; int numbers[ARRAY_SIZE]; for (int count = 0; count < ARRAY_SIZE; count++) numbers[count] = 99;

8. Slide 7- 8 A Closer Look At the Loop

9. Slide 7- 9 Off-By-One Errors An off-by-one error happens when you use array subscripts that are off by one. This can happen when you start subscripts at 1 rather than 0: // This code has an off-by-one error. const int SIZE = 100; int numbers[SIZE]; for (int count = 1; count <= SIZE; count++) numbers[count] = 0;//two mistakes

10. Slide 7- 10 Array Initialization Arrays can be initialized with an initialization list: const int SIZE = 5; int tests[SIZE] = {79,82,91,77,84}; The values are stored in the array in the order in which they appear in the list. The initialization list cannot exceed the array size.

11. Slide 7- 11 Partial Array Initialization If array is initialized with fewer initial values than the size declarator, the remaining elements will be set to 0:

12. Character Arrays Character Arrays are different in various ways from numeric arrays. Declaring Character Arrays – Must always allow room for 1 extra element - the NULL (or: ’ \0’ ) – Example: //Implicit Array Sizing char name[] = "Joe Smith"; //What is sizeof(name); char name[] = {'J', 'o', 'e',' ','S', 'm', 'i', 't', 'h','\0'}; Slide 7- 12

13. Slide 7- 13 Summing and Averaging Array Elements Use a simple loop to add together array elements: int tnum; double average, sum = 0; for(tnum = 0; tnum < SIZE; tnum++) sum += tests[tnum]; Once summed, can compute average: average = sum / SIZE;

14. Slide 7- 14 Example 1: Find the highest score int count; int highest; highest = numbers[0]; for (count = 1; count < SIZE; count++) { if (numbers[count] > highest) highest = numbers[count]; } When this code is finished, the highest variable will contains the highest value in the numbers array.

15. Slide 7- 15 Using Parallel Arrays Parallel arrays: two or more arrays that contain related data A subscript is used to relate arrays: elements at same subscript are related Arrays may be of different types

16. Arrays as Function Arguments When passing an array to a function, it is common to pass array size so that function knows how many elements to process: showScores(tests, ARRAY_SIZE); Array size must also be reflected in prototype, header: void showScores(int [], int); // function prototype void showScores(int tests[], int size) // function header

18. #include using namespace std; void arrayfunc(int num[], int size) { for(int i=0; i<size; i++) { num[i]++; cout<<num[i]<<" "; } void main() { const int size=6; int aa[size] = {10,20,30,40,50,60}; for(int i=0; i<size; i++) cout<<aa[i]<<" "; cout<<"\n"; arrayfunc(aa, size); cout<<"\n"; for(int i=0; i<size; i++) cout<<aa[i]<<" "; cout<<"\n"; }

19. Outline Array Definition Access Array Array Initialization Array Processing 2D Array

20. Slide 7- 20 Two-Dimensional Arrays Can define one array for multiple sets of data Like a table in a spreadsheet Use two size declarators in definition: const int ROWS = 4, COLS = 3; int exams[ROWS][COLS]; First declarator is number of rows; second is number of columns

21. Slide 7- 21 Two-Dimensional Array Representation const int ROWS = 4, COLS = 3; int exams[ROWS][COLS]; Use two subscripts to access element: exams[2][2] = 86; Price = exams[2][1]; Newnum = 4*(exams[1][0]-5); sumRow = exams[0][0]+ exams[0][1]+ exams[0][2]; exams[0][0]exams[0][1]exams[0][2] exams[1][0]exams[1][1]exams[1][2] exams[2][0]exams[2][1]exams[2][2] exams[3][0]exams[3][1]exams[3][2] columns rowsrows

22. Slide 7- 22 2D Array Initialization Two-dimensional arrays are initialized row-by- row: const int ROWS = 2, COLS = 2; int exams[ROWS][COLS] = { {84, 78},{92, 97} }; Can omit inner { }, some initial values in a row – array elements without initial values will be set to 0 or NULL 8478 9297

23. Slide 7- 23 Summing the Columns of a Two-Dimensional Array Given the following definitions: const int NUM_STUDENTS = 3; const int NUM_SCORES = 5; double total; // Accumulator double average; // To hold average scores double scores[NUM_STUDENTS][NUM_SCORES] = {{88, 97, 79, 86, 94}, {86, 91, 78, 79, 84}, {82, 73, 77, 82, 89}};

24. Chapter 8: Searching and Sorting Arrays

25. Linear Search Also called the sequential search Starting at the first element, this algorithm sequentially steps through an array examining each element until it locates the value it is searching for.

26. Linear Search - Example Array numlist contains: Searching for the the value 11, linear search examines 17, 23, 5, and 11 Searching for the the value 7, linear search examines 17, 23, 5, 11, 2, 29, and 3 17235112293

27. Linear Search Algorithm: set found to false; set position to –1; set index to 0 while index < number of elts. and found is false if list[index] is equal to search value found = true position = index end if add 1 to index end while return position

28. A Linear Search Function int searchList(int list[], int numElems, int value) { int index = 0; // Used as a subscript to search array int position = -1; // To record position of search value bool found = false; // Flag to indicate if value was found while (index < numElems && !found) { if (list[index] == value) // If the value is found { found = true; // Set the flag position = index; // Record the value's subscript } index++; // Go to the next element } return position; // Return the position, or -1 }

29. Selection Sort Concept for sort in ascending order: – Locate smallest element in array. Exchange it with element in position 0 – Locate next smallest element in array. Exchange it with element in position 1. – Continue until all elements are arranged in order

30. Selection Sort - Example Array numlist contains: 1.Smallest element is 2. Exchange 2 with element in 1 st position in array: 112293 211293

31. Example (Continued) 2.Next smallest element is 3. Exchange 3 with element in 2 nd position in array: 3.Next smallest element is 11. Exchange 11 with element in 3 rd position in array: 232911 23 29

32. A Selection Sort Function – From Program 8-5 35 void selectionSort(int array[], int size) 36 { 37 int startScan, minIndex, minValue; 38 39 for (startScan = 0; startScan < (size - 1); startScan++) 40 { 41 minIndex = startScan; 42 minValue = array[startScan]; 43 for(int index = startScan + 1; index < size; index++) 44 { 45 if (array[index] < minValue) 46 { 47 minValue = array[index]; 48 minIndex = index; 49 } 50 } 51 array[minIndex] = array[startScan]; 52 array[startScan] = minValue; 53 } 54 }

33. Chapter 11: Structured Data

34. Slide 11- 34 Combining Data into Structures Structure: C++ construct that allows multiple variables to be grouped together General Format: struct { type1 field1; type2 field2;... };

35. Slide 11- 35 Example struct Declaration struct Student { int studentID; string name; short yearInSchool; double gpa; }; structure tag structure members

36. Slide 11- 36 Accessing Structure Members Use the dot (.) operator to refer to members of struct variables: cin >> bill.studentID; getline(cin, bill.name); bill.gpa = 3.75; Member variables can be used in any manner appropriate for their data type

37. Slide 11- 37 Displaying a struct Variable To display the contents of a struct variable, must display each field separately, using the dot operator: cout << bill; // won’t work cout << bill.studentID << endl; cout << bill.name << endl; cout << bill.yearInSchool; cout << " " << bill.gpa;

38. Slide 11- 38 Comparing struct Variables Cannot compare struct variables directly: if (bill == william) // won’t work Instead, must compare on a field basis: if (bill.studentID == william.studentID)...

39. Slide 11- 39 Initializing a Structure struct variable can be initialized when defined: Student s = {11465, "Joan", 2, 3.75}; Can also be initialized member-by-member after definition: s.name = "Joan"; s.gpa = 3.75;

40. Slide 11- 40 Nested Structures A structure can contain another structure as a member: To include a structure within a structure (Nested Structures, p. 642), we follow the same rules for including any data type in a structure. For example, assume that a structure is to consist of a name and a date of birth, where a Date structure, has been declared as struct Date { int month; int day; int year; }; A suitable definition of a structure that includes a name and a Date structure is struct Person { string name; Date birth; };

41. struct Date { int month; int day; int year; }; struct Person { string name; Date birth; }; int main ( void ) { Person employee; employee.name = "Mary Hill"; employee.birth.month = 12; employee.birth.day = 25; employee.birth.year = 2002; cout << employee.name << " birthdate is: “ << employee.birth.month << "/" << employee.birth.day << "/“ << employee.birth.year; return 0; }

42. Slide 11- 42 Arrays of Structures Structures can be defined in arrays Can be used in place of parallel arrays const int NUM_STUDENTS = 20; Student stuList[NUM_STUDENTS]; Individual structures accessible using subscript notation Fields within structures accessible using dot notation: cout << stuList[5].studentID;

43. Slide 11- 43 Structures as Function Arguments Individual structure members may be passed to a function in the same manner as any variable. May pass members of struct variables to functions: computeGPA(stu.gpa); May pass entire struct variables to functions: showData(stu); Can use reference parameter if function needs to modify contents of structure variable

44. Slide 11- 44 Structures as Function Arguments Individual structure members may be passed to a function in the same manner as any variable. May pass members of struct variables to functions: computeGPA(stu.gpa); May pass entire struct variables to functions: showData(stu); Can use reference parameter if function needs to modify contents of structure variable

45. struct Employee // declare a global type { int id_number; double pay_rate; double hours; }; double calcNet(double, double); // function prototype int main ( void ) { Employee emp = {6782, 8.93, 40.5}; double net_pay; net_pay = calcNet(emp.pay_rate, emp.hours); //PASS BY VALUE cout << setw(10) << fixed << showpoint << setprecision(2); cout << "The net pay for employee " << emp.id_number << " is $" << net_pay << endl; return 0; } double calcNet(double pay_rate, double hours) { return (pay_rate * hours); } //PASS BY VALUE //Output: The net pay for employee 6782 is $361.66 This example passes copies of the values stored in structure members emp.pay_rate and emp.hours to the function named calcNet( ).

46. struct Employee // declare a global type { int id_number; double pay_rate; double hours; }; double calcNet(Employee); // function prototype int main ( void ) { Employee emp = {6782, 8.93, 40.5}; double net_pay; net_pay = calcNet(emp); cout << setw(10) << fixed <<showpoint << setprecision(2); cout << "The net pay for employee " << emp.id_number << " is $" << net_pay << endl; return 0; } double calcNet(Employee temp) {return (temp.pay_rate * temp.hours); } Output The net pay for employee 6782 is $361.66

47. Slide 11- 47 Returning a Structure from a Function - Example Student getStudentData() { Student tempStu; cin >> tempStu.studentID; getline(cin, tempStu.pData.name); getline(cin, tempStu.pData.address); getline(cin, tempStu.pData.city); cin >> tempStu.yearInSchool; cin >> tempStu.gpa; return tempStu; }