Ch7

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Ch7

  1. 1. 1 Starting Out with C++, 3rd Edition Chapter 7 – Arrays
  2. 2. 2 Starting Out with C++, 3rd Edition 7.1 Arrays Hold Multiple values • Unlike regular variables, arrays can hold multiple values.
  3. 3. 3 Starting Out with C++, 3rd Edition Figure 7-1 int count Enough memory for 1 int 12345 float price Enough memory for 1 float 56.981 char letter Enough memory for 1 char A
  4. 4. 4 Starting Out with C++, 3rd Edition Figure 7-2
  5. 5. 5 Starting Out with C++, 3rd Edition Table 7-1 Array Declaration Number of Elements Size of Each Element S ize of the Array c h a r l e t t e r s [ 2 5 ] ; 25 1 byte 25 bytes s h o r t r i n g s [ 1 0 0 ] ; 100 2 bytes 200 bytes i n t m i l e s [ 8 4 ] ; 84 4 bytes 336 bytes f l o a t t e m p [ 1 2 ] ; 12 4 bytes 48 bytes d o u b l e d D i s t a n c e [ 1 0 0 0 ] ; 1000 8 bytes 8000 bytes
  6. 6. 6 Starting Out with C++, 3rd Edition 7.2 Accessing Array elements • The individual elements of an array are assigned unique subscripts. These subscripts are used to access the elements.
  7. 7. 7 Starting Out with C++, 3rd Edition Program 7-1 // This program asks the user for the number of hours worked // by 6 employees. It uses a 6-element int array to store the // values. #include <iostream.h> void main(void) { short hours[6]; cout << "Enter the hours worked by six employees: "; cin >> hours[0]; cin >> hours[1]; cin >> hours[2]; cin >> hours[3];
  8. 8. 8 Starting Out with C++, 3rd Edition Program continues cin >> hours[4]; cin >> hours[5]; cout << "The hours you entered are:"; cout << " " << hours[0]; cout << " " << hours[1]; cout << " " << hours[2]; cout << " " << hours[3]; cout << " " << hours[4]; cout << " " << hours[5] << endl; }
  9. 9. 9 Starting Out with C++, 3rd Edition Program Output with Example Input Enter the hours worked by six employees: 20 12 40 30 30 15 [Enter] The hours you entered are: 20 12 40 30 30 15
  10. 10. 10 Starting Out with C++, 3rd Edition Figure 7-7
  11. 11. 11 Starting Out with C++, 3rd Edition Program 7-2 // This program asks the user for the number of hours worked // by 6 employees. It uses a 6-element short array to store the // values. #include <iostream.h> void main(void) { short hours[6]; cout << "Enter the hours worked by six employees: "; for (int count = 0; count < 6; count++) cin >> hours[count]; cout << "The hours you entered are:"; for (count = 0; count < 6; count++) cout << " " << hours[count]; cout << endl; }
  12. 12. 12 Starting Out with C++, 3rd Edition Program Output with Example Input Enter the hours worked by six employees: 20 12 40 30 30 15 [Enter] The hours you entered are: 20 12 40 30 30 15
  13. 13. 13 Starting Out with C++, 3rd Edition Program 7-3 // This program asks the user for the number of hours worked // by 6 employees. It uses a 6-element short array to store the // values. #include<iostream.h> void main(void) { short hours[6]; cout << "Enter the hours worked by six employees.n"; for (int count = 1; count <= 6; count++) { cout << "Employee " << count << ": "; cin >> hours[count - 1]; } cout << "The hours you entered aren";
  14. 14. 14 Starting Out with C++, 3rd Edition Program continues for (count = 1; count <= 6; count++) { cout << "Employee " << count << ": "; cout << hours[count - 1] << endl; } }
  15. 15. 15 Starting Out with C++, 3rd Edition Program Output with Example Input Enter the hours worked by six employees. Employee 1: 20 [Enter] Employee 2: 12 [Enter] Employee 3: 40 [Enter] Employee 4: 30 [Enter] Employee 5: 30 [Enter] Employee 6: 15 [Enter] The hours you entered are Employee 1: 20 Employee 2: 12 Employee 3: 40 Employee 4: 30 Employee 5: 30 Employee 6: 15
  16. 16. 16 Starting Out with C++, 3rd Edition 7.3 No Bounds Checking in C++ • C++ gives you the freedom to store data past an array’s boundaries.
  17. 17. 17 Starting Out with C++, 3rd Edition Program 7-4 // This program unsafely accesses an area of memory by writing // values beyond an array's boundary. // WARNING: If you compile and run this program, it could cause // the computer to crash. #include <iostream.h> void main(void) { short values[3]; // An array of 3 short integers. cout << "I will store 5 numbers in a 3 element array!n"; for (int count = 0; count < 5; count++) values[count] = 100; cout << "If you see this message, it means the computern"; cout << "has not crashed! Here are the numbers:n"; for (int count = 0; count < 5; count++) cout << values[count] << endl; }
  18. 18. 18 Starting Out with C++, 3rd Edition Figure 7-8
  19. 19. 19 Starting Out with C++, 3rd Edition 7.4 Array Initialization • Arrays may be initialized when they are declared.
  20. 20. 20 Starting Out with C++, 3rd Edition Program 7-5 // This program displays the number of days in each month. // It uses a 12-element int array. #include <iostream.h> void main(void) { int days[12]; days[0] = 31; // January days[1] = 28; // February days[2] = 31; // March days[3] = 30; // April days[4] = 31; // May days[5] = 30; // June days[6] = 31; // July
  21. 21. 21 Starting Out with C++, 3rd Edition Program continues days[7] = 31; // August days[8] = 30; // September days[9] = 31; // October days[10] = 30; // November days[11] = 31; // December for (int count = 0; count < 12; count++) { cout << "Month " << (count + 1) << " has "; cout << days[count] << " days.n"; } }
  22. 22. 22 Starting Out with C++, 3rd Edition Program Output Month 1 has 31 days. Month 2 has 28 days. Month 3 has 31 days. Month 4 has 30 days. Month 5 has 31 days. Month 6 has 30 days. Month 7 has 31 days. Month 8 has 31 days. Month 9 has 30 days. Month 10 has 31 days. Month 11 has 30 days. Month 12 has 31 days.
  23. 23. 23 Starting Out with C++, 3rd Edition Program 7-6 // This program displays the number of days in each month. // It uses a 12-element int array. #include <iostream.h> void main(void) { int days[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}; for (int count = 0; count < 12; count++) { cout << "Month " << (count + 1) << " has "; cout << days[count] << " days.n"; } }
  24. 24. 24 Starting Out with C++, 3rd Edition Program Output Month 1 has 31 days. Month 2 has 28 days. Month 3 has 31 days. Month 4 has 30 days. Month 5 has 31 days. Month 6 has 30 days. Month 7 has 31 days. Month 8 has 31 days. Month 9 has 30 days. Month 10 has 31 days. Month 11 has 30 days. Month 12 has 31 days.
  25. 25. 25 Starting Out with C++, 3rd Edition Program 7-7 // This program uses an array of ten characters to store the // first ten letters of the alphabet. The ASCII codes of the // characters are displayed. #include <iostream.h> void main(void) { char letters[10] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J'}; cout << "Character" << "t" << "ASCII Coden"; cout << "--------" << "t" << "----------n"; for (int count = 0; count < 10; count++) { cout << letters[count] << "tt"; cout << int(letters[count]) << endl; } }
  26. 26. 26 Starting Out with C++, 3rd Edition Program Output Character ASCII Code --------- ---------- A 65 B 66 C 67 D 68 E 69 F 70 G 71 H 72 I 73 J 74
  27. 27. 27 Starting Out with C++, 3rd Edition Partial Array Initialization • When an array is being initialized, C++ does not require a value for every element. int numbers[7] = {1, 2, 4, 8};
  28. 28. 28 Starting Out with C++, 3rd Edition Program 7-8 // This program has a partially initialized array. #include <iostream.h> void main(void) { int numbers[7] = {1, 2, 4, 8}; // Initialize the // first 4 elements. cout << "Here are the contents of the array:n"; for (int index = 0; index < 7; index++) cout << numbers[index] << endl; }
  29. 29. 29 Starting Out with C++, 3rd Edition Program Output Here are the contents of the array: 1 2 4 8 0 0 0
  30. 30. 30 Starting Out with C++, 3rd Edition Implicit Array Sizing • It is possible to declare an array without specifying its size, as long as you provide an initialization list. float ratings[] = {1.0, 1.5, 2.0, 2.5, 3.0};
  31. 31. 31 Starting Out with C++, 3rd Edition Initializing With Strings • When initializing a character array with a string, simply enclose the string in quotation marks: char name[] = “Warren”;
  32. 32. 32 Starting Out with C++, 3rd Edition Figure 7-11
  33. 33. 33 Starting Out with C++, 3rd Edition Program 7-9 // This program displays the contents of two char arrays. #include <iostream.h> void main(void) { char name1[] = "Holly"; char name2[] = {'W', 'a', 'r', 'r', 'e', 'n', '0'}; cout << name1 << endl; cout << name2 << endl; }
  34. 34. 34 Starting Out with C++, 3rd Edition Program Output Holly Warren
  35. 35. 35 Starting Out with C++, 3rd Edition 7.5 Processing Array Contents • Individual array elements are processed like any other type of variable.
  36. 36. 36 Starting Out with C++, 3rd Edition Program 7-10 // This program stores, in an array, the hours worked by 5 // employees who all make the same hourly wage. #include <iostream.h> void main(void) { int hours[5]; float payRate; cout << "Enter the hours worked by 5 employees who alln"; cout << "earn the same hourly rate.n"; for (int index = 0; index < 5; index++) { cout << "Employee #" << (index + 1) << ": "; cin >> hours[index]; }
  37. 37. 37 Starting Out with C++, 3rd Edition Program continues cout << "Enter the hourly pay rate for all the employees: "; cin >> payRate; cout << "Here is the gross pay for each employee:n"; cout.precision(2); cout.setf(ios::fixed | ios::showpoint); for (index = 0; index < 5; index++) { float grossPay = hours[index] * payRate; cout << "Employee #" << (index + 1); cout << ": $" << grossPay << endl; } }
  38. 38. 38 Starting Out with C++, 3rd Edition Program Output with Example Input Enter the hours worked by 5 employees who all earn the same hourly rate. Employee #1: 5 [Enter] Employee #2: 10 [Enter] Employee #3: 15 [Enter] Employee #4: 20 [Enter] Employee #5: 40 [Enter] Enter the hourly pay rate for all the employees: 12.75 [Enter] Here is the gross pay for each employee: Employee #1: $63.75 Employee #2: $127.50 Employee #3: $191.25 Employee #4: $255.00 Employee #5: $510.00
  39. 39. 39 Starting Out with C++, 3rd Edition Program 7-11 // This program stores, in an array, the hours worked by 5 // employees who all make the same hourly wage. It then // displays the gross pay, including any overtime. #include <iostream.h> // Constant for defining the array size void main(void) { int hours[5]; float payRate; cout << "Enter the hours worked by 5 employees who alln"; cout << "earn the same hourly rate.n"; for (int index = 0; index < 5; index++) { cout << "Employee #" << (index + 1) << ": "; cin >> hours[index]; }
  40. 40. 40 Starting Out with C++, 3rd Edition Program continues cout << "Enter the hourly pay rate for all the employees: "; cin >> payRate; cout << "Here is the gross pay for each employee:n"; cout.precision(2); cout.setf(ios::fixed | ios::showpoint); for (index = 0; index < 5; index++) { float grossPay, overTime; if (hours[index] > 40) { // Calculate pay for 40 hours. grossPay = 40 * payRate; // Calculate overtime pay. overTime = (hours[index] - 40) * 1.5 * payRate; // Add regular pay and overtime pay. grossPay += overTime; }
  41. 41. 41 Starting Out with C++, 3rd Edition Program continues else grossPay = hours[index] * payRate; cout << "Employee #" << (index + 1); cout << ": $" << grossPay << endl; } }
  42. 42. 42 Starting Out with C++, 3rd Edition Program Output with Example Input Enter the hours worked by 5 employees who all earn the same hourly rate. Employee #1: 10 [Enter] Employee #2: 20 [Enter] Employee #3: 50 [Enter] Employee #4: 40 [Enter] Employee #5: 60 [Enter] Enter the hourly pay rate for all the employees: 12.75 [Enter] Here is the gross pay for each employee: Employee #1: $127.50 Employee #2: $255.00 Employee #3: $701.25 Employee #4: $510.00 Employee #5: $892.50
  43. 43. 43 Starting Out with C++, 3rd Edition 7.6 Focus on Software Engineering: Parallel Arrays • By using he same subscript, you can build relationships between data stored in two or more arrays.
  44. 44. 44 Starting Out with C++, 3rd Edition Program 7-12 // This program stores, in two arrays, the hours worked by 5 // employees, and their hourly pay rates. #include <iostream.h> // Constant for defining the array size const int numEmps = 5; void main(void) { int hours[numEmps]; float payRate[numEmps]; cout << "Enter the hours worked by “ << numEmps << “ employees and theirn"; cout << "hourly rates.n"; for (int index = 0; index < numEmps; index++) { cout << "hours worked by employee #" << (index + 1); cout << ": ";
  45. 45. 45 Starting Out with C++, 3rd Edition Program continues cin >> hours[index]; cout << "Hourly pay rate for employee #"; cout << (index + 1) << ": "; cin >> payRate[index]; } cout << "Here is the gross pay for each employee:n"; cout.precision(2); cout.setf(ios::fixed | ios::showpoint); for (index = 0; index < numEmps; index++) { float grossPay = hours[index] * payRate[index]; cout << "Employee #" << (index + 1); cout << ": $" << grossPay << endl; } }
  46. 46. 46 Starting Out with C++, 3rd Edition Program Output with Example Input Enter the hours worked by 5 employees and their hourly rates. hours worked by employee #1: 10 [Enter] Hourly pay rate for employee #1: 9.75 [Enter] hours worked by employee #2: 15 [Enter] Hourly pay rate for employee #2: 8.62 [Enter] hours worked by employee #3: 20 [Enter] Hourly pay rate for employee #3: 10.50 [Enter] hours worked by employee #4: 40 [Enter] Hourly pay rate for employee #4: 18.75 [Enter] hours worked by employee #5: 40 [Enter] Hourly pay rate for employee #5: 15.65 [Enter] Here is the gross pay for each employee: Employee #1: $97.50 Employee #2: $129.30 Employee #3: $210.00
  47. 47. 47 Starting Out with C++, 3rd Edition 7.7 Thou Shalt Not Assign • You cannot use the assignment operator to copy one array’s contents to another. for (int count=0; count < 4; count++) newVal[count] = oldVal[count];
  48. 48. 48 Starting Out with C++, 3rd Edition Table 7-2 Expression Value O ld V a lu e s [ 0 ] 10 (Contents of Element 0 of O ld V a lu e s ) O ld V a lu e s [ 1 ] 100 (Contents of Element 1 of O ld V a lu e s ) O ld V a lu e s [ 2 ] 200 (Contents of Element 2 of O ld V a lu e s ) O ld V a lu e s [ 3 ] 300 (Contents of Element 3 of O ld V a lu e s ) N e w V a lu e s 8012 (Memory Address of N e w V a lu e s ) O ld V a lu e s 8024 (Memory Address of O ld V a lu e s )
  49. 49. 49 Starting Out with C++, 3rd Edition 7.8 Printing the Contents of an Array • To display the contents of an array, you must use a loop to display the contents of each element. int array[5] = { 10, 20, 30, 40, 50 }; for (int count = 0; count < 5; count++) cout << array[count] << endl;
  50. 50. 50 Starting Out with C++, 3rd Edition 7.9 Arrays As Function Arguments • To pass an array as an argument to a function, pass the name of the array.
  51. 51. 51 Starting Out with C++, 3rd Edition Program 7-13 // This program demonstrates that an array element is passed // to a function like any other variable. #include <iostream.h> void ShowValue(int); // Function prototype void main(void) { int collection[8] = {5, 10, 15, 20, 25, 30, 35, 40}; for (int Cycle = 0; Cycle < 8; Cycle++) ShowValue(collection[Cycle]); }
  52. 52. 52 Starting Out with C++, 3rd Edition Program continues //************************************ // Definition of function showValue. * // This function accepts an integer argument. * // The value of the argument is displayed. * //************************************ void ShowValue(int Num) { cout << Num << " "; }
  53. 53. 53 Starting Out with C++, 3rd Edition Program Output 5 10 15 20 25 30 35 40
  54. 54. 54 Starting Out with C++, 3rd Edition Program 7-14 // This program demonstrates an array being passed to a function. #include <iostream.h> void showValues(int []); // Function prototype void main(void) { int collection[8] = {5, 10, 15, 20, 25, 30, 35, 40}; showValues(collection); // Passing address of array collection } //*********************************************** // Definition of function showValues. * // This function accepts an array of 8 integers * // as its argument. The contents of the array * // is displayed. * //*********************************************** void showValues(int nums[]) { for (int index = 0; index < 8; index++) cout << nums[index] << " "; }
  55. 55. 55 Starting Out with C++, 3rd Edition Program Output 5 10 15 20 25 30 35 40
  56. 56. 56 Starting Out with C++, 3rd Edition Program 7-15 // This program demonstrates an array being passed to a function. #include <iostream.h> void showValues(int []); // Function prototype void main(void) { int set1[8] = {5, 10, 15, 20, 25, 30, 35, 40}; int set2[8] = {2, 4, 6, 8, 10, 12, 14, 16}; showValues(set1); cout << endl; showValues(set2); } //*********************************************** // Definition of function showValues. * // This function accepts an array of 8 integers * // as its argument. The contents of the array * // is displayed. * //*********************************************** void showValues(int nums[]) { for (int index = 0; index < 8; index++) cout << nums[index] << " "; }
  57. 57. 57 Starting Out with C++, 3rd Edition Program Output 5 10 15 20 25 30 35 40 2 4 6 8 10 12 14 16
  58. 58. 58 Starting Out with C++, 3rd Edition Program 7-16 // This program uses a function that can display the contents // of an integer array of any size. #include <iostream.h> void showValues(int [], int); // Function prototype void main(void) { int set1[8] = {5, 10, 15, 20, 25, 30, 35, 40}; int set2[4] = {2, 4, 6, 8}; int set3[12] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12}; showValues(set1, 8); cout << endl; showValues(set2, 4); cout << endl; showValues(set3, 12); }
  59. 59. 59 Starting Out with C++, 3rd Edition Program continues //*********************************************** // Definition of function showValues. * // This function displays the contents of the * // array passed into nums. The value passed * // into elements is the number of elements in * // the nums array. * //*********************************************** void showValues(int nums[], int elements) { for (int index = 0; index < elements; index++) cout << nums[index] << " "; }
  60. 60. 60 Starting Out with C++, 3rd Edition Program Output 5 10 15 20 25 30 35 40 2 4 6 8 1 2 3 4 5 6 7 8 9 10 11 12
  61. 61. 61 Starting Out with C++, 3rd Edition Program 7-17 // This program uses a function that doubles the contents of // the elements within an array. #include <iostream.h> void doubleArray(int [], int); // Function prototype const int arraySize = 12; void main(void) { int set[arraySize] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12}; cout << "The arrays values are:n"; for (int index = 0; index < arraySize; index++) cout << set[index] << " "; cout << endl; doubleArray(set, arraySize); cout << "After calling doubleArray, the values are:n";
  62. 62. 62 Starting Out with C++, 3rd Edition Program continues for (int index = 0; index < arraySize; index++) cout << set[index] << " "; cout << endl; } //************************************************** // Definition of function doubleArray. * // This function doubles the value of each element * // in the array passed into nums. * // The value passed into size is the number of * // elements in the nums array. * //************************************************** void doubleArray(int nums[], int size) { for (int index = 0; index < size; index++) nums[index] *= 2; }
  63. 63. 63 Starting Out with C++, 3rd Edition Program Output The array values are: 1 2 3 4 5 6 7 8 9 10 11 12 After calling doubleArray, the values are: 2 4 6 8 10 12 14 16 18 20 22 24
  64. 64. 64 Starting Out with C++, 3rd Edition 7.10 Two-dimensional Arrays • A two-dimensional array is like several identical arrays put together. It is useful for storing multiple sets of data.
  65. 65. 65 Starting Out with C++, 3rd Edition Program 7-18 // This program demonstrates a two-dimensional array. #include <iostream.h> void main(void) { float sales[3][4]; // 2D array, 3 rows and 4 columns. float totalSales = 0; // To hold the total sales. int dir, qtr; // Loop counters.
  66. 66. 66 Starting Out with C++, 3rd Edition Program continues cout << "This program will calculate the total sales ofn"; cout << "all the company's divisions.n"; cout << "Enter the following sales information:nn"; // Nested loops to fill the array with quarterly // sales figures for each division. for (div = 0; div < 3; div++) { for (qtr = 0; qtr < 4; qtr++) { cout << "Division " << (div + 1); cout << ", Quarter " << (qtr + 1) << ": $"; cin >> sales[div][qtr]; } cout << endl; // Print blank line. }
  67. 67. 67 Starting Out with C++, 3rd Edition Program continues // Nested loops to add all the elements. for (div = 0; div < 3; div++) for (qtr = 0; qtr < 4; qtr++) totalSales += sales[div][qtr]; cout.precision(2); cout.setf(ios::fixed | ios::showpoint); cout << "The total sales for the company are: $"; cout << totalSales << endl; }
  68. 68. 68 Starting Out with C++, 3rd Edition Program Output with Example Input This program will calculate the total sales of all the company's divisions. Enter the following sales information: Division 1, Quarter 1: $31569.45 [Enter] Division 1, Quarter 2: $29654.23 [Enter] Division 1, Quarter 3: $32982.54 [Enter] Division 1, Quarter 4: $39651.21 [Enter] Division 2, Quarter 1: $56321.02 [Enter] Division 2, Quarter 2: $54128.63 [Enter] Division 2, Quarter 3: $41235.85 [Enter] Division 2, Quarter 4: $54652.33 [Enter]
  69. 69. 69 Starting Out with C++, 3rd Edition Output continues Division 3, Quarter 1: $29654.35 [Enter] Division 3, Quarter 2: $28963.32 [Enter] Division 3, Quarter 3: $25353.55 [Enter] Division 3, Quarter 4: $32615.88 [Enter] The total sales for the company are: $456782.34
  70. 70. 70 Starting Out with C++, 3rd Edition Passing Two-dimensional Arrays to Functions • When a two-dimensional array is passed to a function, the parameter type must contain a size declarator for the number of columns.
  71. 71. 71 Starting Out with C++, 3rd Edition 7.11 Arrays of Strings • A two-dimensional array of characters can be used as an array of C-strings.
  72. 72. 72 Starting Out with C++, 3rd Edition Program 7-20 // This program displays the number of days in each month. // It uses a two-dimensional character array to hold the // names of the months and an int array to hold the number // of days. #include <iostream.h> void main(void) { char months[12][10] = {"January", "February", "March", "April", "May", "June", "July", "August", "September”, "October", "November","December"}; int days[12] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}; for (int count = 0; count < 12; count++) { cout << months[count] << " has "; cout << days[count] << " days.n"; } }
  73. 73. 73 Starting Out with C++, 3rd Edition Program 7-20 (continued) Program Output January has 31 days. February has 28 days. March has 31 days. April has 30 days. May has 31 days. June has 30 days. July has 31 days. August has 31 days. September has 30 days. October has 31 days. November has 30 days. December has 31 days.
  74. 74. 74 Starting Out with C++, 3rd Edition Three Dimensional Arrays and Beyond • C++ allows you to create arrays with virtually any number of dimensions. • Here is an example of a three-dimensional array declaration: float seat[3][5][8];
  75. 75. 75 Starting Out with C++, 3rd Edition 7.14 Introduction to the STL vector • The Standard Template Library (or STL) is a collection of data types and algorithms that you may use in your programs. These data types and algorithms are programmer- defined. They are not part of the C++ language, but were created in addition to the built-in data types.
  76. 76. 76 Starting Out with C++, 3rd Edition 7.14 Introduction to the STL vector • The data types that are defined in the STL are commonly called containers, because they store and organize data. • There are two types of containers in the STL: sequence containers and associative containers. • The vector data type is a sequence container.
  77. 77. 77 Starting Out with C++, 3rd Edition 7.14 Introduction to the STL vector • A vector is like an array in the following ways: – A vector holds a sequence of values, or elements. – A vector stores its elements in contiguous memory locations. – You can use the array subscript operator [] to read the individual elements in the vector
  78. 78. 78 Starting Out with C++, 3rd Edition 7.14 Introduction to the STL vector • However, a vector offers several advantages over arrays. Here are just a few: – You do not have to declare the number of elements that the vector will have. – If you add a value to a vector that is already full, the vector will automatically increase its size to accommodate the new value. – vectors can report the number of elements they contain.
  79. 79. 79 Starting Out with C++, 3rd Edition Declaring a vector • To use vectors in your program, you must first #include the vector header file with the following statement: #include <vector> Note: There is no .h at the end of the file name.
  80. 80. 80 Starting Out with C++, 3rd Edition Declaring a vector • The next step is to include the following statement after your #include statements: using namespace std; The STL uses namespaces to organize the names of its data types and algorithms.
  81. 81. 81 Starting Out with C++, 3rd Edition Declaring a vector • Now you are ready to declare an actual vector object. Here is an example: vector<int> numbers; The statement above declares numbers as a vector of ints.
  82. 82. 82 Starting Out with C++, 3rd Edition Declaring a vector • You can declare a starting size, if you prefer. Here is an example: vector<int> numbers(10); The statement above declares numbers as a vector of 10 ints.
  83. 83. 83 Starting Out with C++, 3rd Edition Other examples of vector Declarations Declaration Format Description vector<float> amounts; Declares amounts as an empty vector of floats. vector<int> scores(15); Declares scores as a vector of 15 ints. vector<char> letters(25, 'A'); Declares letters as a vector of 25 characters. Each element is initialized with 'A'. vector<double> values2(values1); Declares values2 as a vector of doubles. All the elements of values1, which also a vector of doubles, are copied to value2.
  84. 84. 84 Starting Out with C++, 3rd Edition Storing and Retrieving Values in a vector • To store a value in an element that already exists in a vector, you may use the array subscript operator [].
  85. 85. 85 Starting Out with C++, 3rd Edition Program 7-23 // This program stores, in two vectors, the hours worked by 5 // employees, and their hourly pay rates. #include <iostream.h> #include <vector> // Needed to declare vectors using namespace std; void main(void) { vector<int> hours(5); // Declare a vector of 5 integers vector<float> payRate(5); // Declare a vector of 5 floats cout << "Enter the hours worked by 5 employees and theirn"; cout << "hourly rates.n"; for (int index = 0; index < 5; index++) { cout << "Hours worked by employee #" << (index + 1); cout << ": "; cin >> hours[index]; cout << "Hourly pay rate for employee #"; cout << (index + 1) << ": "; cin >> payRate[index]; }
  86. 86. 86 Starting Out with C++, 3rd Edition Program 7-23 (continued) cout << "Here is the gross pay for each employee:n"; cout.precision(2); cout.setf(ios::fixed | ios::showpoint); for (index = 0; index < 5; index++) { float grossPay = hours[index] * payRate[index]; cout << "Employee #" << (index + 1); cout << ": $" << grossPay << endl; } }
  87. 87. 87 Starting Out with C++, 3rd Edition Program 7-23 (continued) Program Output with Example Input Shown in Bold Enter the hours worked by 5 employees and their hourly rates. Hours worked by employee #1: 10 [Enter] Hourly pay rate for employee #1: 9.75 [Enter] Hours worked by employee #2: 15 [Enter] Hourly pay rate for employee #2: 8.62 [Enter] Hours worked by employee #3: 20 [Enter] Hourly pay rate for employee #3: 10.50 [Enter] Hours worked by employee #4: 40 [Enter] Hourly pay rate for employee #4: 18.75 [Enter] Hours worked by employee #5: 40 [Enter] Hourly pay rate for employee #5: 15.65 [Enter] Here is the gross pay for each employee: Employee #1: $97.50 Employee #2: $129.30 Employee #3: $210.00 Employee #4: $750.00 Employee #5: $626.00
  88. 88. 88 Starting Out with C++, 3rd Edition Using the push_back Member Function • You cannot use the [] operator to access a vector element that does not exist. • To store a value in a vector that does not have a starting size, or is already full, use the push_back member function. Here is an example: numbers.push_back(25);
  89. 89. 89 Starting Out with C++, 3rd Edition Program 7-24 // This program stores, in two vectors, the hours worked by a specified // number of employees, and their hourly pay rates. #include <iostream.h> #include <vector> // Needed to declare vectors using namespace std; void main(void) { vector<int> hours; // hours is an empty vector vector<float> payRate; // payRate is an empty vector int numEmployees; // The number of employees cout << "How many employees do you have? "; cin >> numEmployees; cout << "Enter the hours worked by " << numEmployees; cout << " employees and their hourly rates.n";
  90. 90. 90 Starting Out with C++, 3rd Edition Program 7-24 (continued) for (int index = 0; index < numEmployees; index++) { int tempHours; // To hold the number of hours entered float tempRate; // To hold the payrate entered cout << "Hours worked by employee #" << (index + 1); cout << ": "; cin >> tempHours; hours.push_back(tempHours); // Add an element to hours cout << "Hourly pay rate for employee #"; cout << (index + 1) << ": "; cin >> tempRate; payRate.push_back(tempRate); // Add an element to payRate } cout << "Here is the gross pay for each employee:n"; cout.precision(2); cout.setf(ios::fixed | ios::showpoint); for (index = 0; index < numEmployees; index++) { float grossPay = hours[index] * payRate[index]; cout << "Employee #" << (index + 1); cout << ": $" << grossPay << endl; } }
  91. 91. 91 Starting Out with C++, 3rd Edition Program 7-24 (continued) Program Output with Example Input Shown in Bold How many employees do you have? 3 [Enter] Enter the hours worked by 3 employees and their hourly rates. Hours worked by employee #1: 40 [Enter] Hourly pay rate for employee #1: 12.63 [Enter] Hours worked by employee #2: 25 [Enter] Hourly pay rate for employee #2: 10.35 [Enter] Hours worked by employee #3: 45 [Enter] Hourly pay rate for employee #3: 22.65 [Enter] Here is the gross pay for each employee: Employee #1: $505.20 Employee #2: $258.75 Employee #3: $1019.25
  92. 92. 92 Starting Out with C++, 3rd Edition Determining the Size of a vector • Unlike arrays, vectors can report the number of elements they contain. This is accomplished with the size member function. Here is an example of a statement that uses the size member function: numValues = set.size(); • In the statement above, assume that numValues is an int, and set is a vector. After the statement executes, numValues will contain the number of elements in the vector set.
  93. 93. 93 Starting Out with C++, 3rd Edition Determining the Size of a vector • Example: void showValues(vector<int> vect) { for (int count = 0; count < vect.size(); count++) cout << vect[count] << endl; }
  94. 94. 94 Starting Out with C++, 3rd Edition Program 7-25 // This program demonstrates the vector size // member function. #include <iostream.h> #include <vector> using namespace std; // Function prototype void showValues(vector<int>); void main(void) { vector<int> values; for (int count = 0; count < 7; count++) values.push_back(count * 2); showValues(values); }
  95. 95. 95 Starting Out with C++, 3rd Edition Program 7-25 (continued) //************************************************** // Definition of function showValues. * // This function accepts an int vector as its * // argument. The value of each of the vector's * // elements is displayed. * //************************************************** void showValues(vector<int> vect) { for (int count = 0; count < vect.size(); count++) cout << vect[count] << endl; }
  96. 96. 96 Starting Out with C++, 3rd Edition Program 7-25 (continued) Program Output 0 2 4 6 8 10 12
  97. 97. 97 Starting Out with C++, 3rd Edition Removing Elements from a vector • Use the pop_back member function to remove the last element from a vector. collection.pop_back(); The statement above removes the last element from the collection vector.
  98. 98. 98 Starting Out with C++, 3rd Edition Program 7-26 // This program demosntrates the vector size member function. #include <iostream.h> #include <vector> using namespace std; void main(void) { vector<int> values; // Store values in the vector values.push_back(1); values.push_back(2); values.push_back(3); cout << "The size of values is " << values.size() << endl; // Remove a value from the vector cout << "Popping a value from the vector...n"; values.pop_back(); cout << "The size of values is now " << values.size() << endl;
  99. 99. 99 Starting Out with C++, 3rd Edition Program 7-26 (continued) // Now remove another value from the vector cout << "Popping a value from the vector...n"; values.pop_back(); cout << "The size of values is now " << values.size() << endl; // Remove the last value from the vector cout << "Popping a value from the vector...n"; values.pop_back(); cout << "The size of values is now " << values.size() << endl; } Program Output The size of values is 3 Popping a value from the vector... The size of values is now 2 Popping a value from the vector... The size of values is now 1 Popping a value from the vector... The size of values is now 0
  100. 100. 100 Starting Out with C++, 3rd Edition Clearing a vector • To completely clear the contents of a vector, use the clear member function. Here is an example: numbers.clear(); After the statement above executes, the numbers vector will be cleared of all its elements.
  101. 101. 101 Starting Out with C++, 3rd Edition Program 7-27 // This program demosntrates the vector size member function. #include <iostream.h> #include <vector> using namespace std; void main(void) { vector<int> values(100); cout << "The values vector has “ << values.size() << " elements.n"; cout << "I will call the clear member function...n"; values.clear(); cout << "Now, the values vector has “ << values.size() << " elements.n"; }
  102. 102. 102 Starting Out with C++, 3rd Edition Program 7-27 (continued) Program Output The values vector has 100 elements. I will call the clear member function... Now, the values vector has 0 elements.
  103. 103. 103 Starting Out with C++, 3rd Edition Detecting an Empty vector • To determine if a vector is empty, use the empty member function. The function returns true if the vector is empty, and false if the vector has elements stored in it. Here is an example of its use: if (set.empty()) cout << "No values in set.n";
  104. 104. 104 Starting Out with C++, 3rd Edition Program 7-28 // This program demosntrates the vector's empty member function. #include <iostream.h> #include <vector> using namespace std; // Function prototype float avgVector(vector<int>); void main(void) { vector<int> values; int numValues; float average; cout << "How many values do you wish to average? "; cin >> numValues;
  105. 105. 105 Starting Out with C++, 3rd Edition Program 7-28 (continued) for (int count = 0; count < numValues; count++) { int tempValue; cout << "Enter a value: "; cin >> tempValue; values.push_back(tempValue); } average = avgVector(values); cout << "Average: " << average << endl; } //************************************************************* // Definition of function avgVector. * // This function accepts an int vector as its argument. If * // the vector contains values, the function returns the * // average of those values. Otherwise, an error message is * // displayed and the function returns 0.0. * //*************************************************************
  106. 106. 106 Starting Out with C++, 3rd Edition Program 7-28 (continued) float avgVector(vector<int> vect) { int total = 0; // accumulator float avg; // average if (vect.empty()) // Determine if the vector is empty { cout << "No values to average.n"; avg = 0.0; } else { for (int count = 0; count < vect.size(); count++) total += vect[count]; avg = total / vect.size(); } return avg; }
  107. 107. 107 Starting Out with C++, 3rd Edition Program 7-28 (continued) Program Output with Example Input Shown in Bold How many values do you wish to average? Enter a value: 12 Enter a value: 18 Enter a value: 3 Enter a value: 7 Enter a value: 9 Average: 9 Program Output with Example Input Shown in Bold How many values do you wish to average? 0 No values to average. Average: 0
  108. 108. 108 Starting Out with C++, 3rd Edition Summary of vector Member Functions Member Function Description at(element) Returns the value of the element located at element in the vector. Example: x = vect.at(5); The statement above assigns the value of the 5th element of vect to x. capacity() Returns the maximum number of elements that may be stored in the vector without additional memory being allocated. (This is not the same value as returned by the size member function). Example: x = vect.capacity(); The statement above assigns the capacity of vect to x.
  109. 109. 109 Starting Out with C++, 3rd Edition Summary of vector Member Functions clear() Clears a vector of all its elements. Example: vect.clear(); The statement above removes all the elements from vect. empty() Returns true if the vector is empty. Otherwise, it returns false. Example: if (vect.empty()) cout << "The vector is empty."; The statement above displays the message if vect is empty. pop_back() Removes the last element from the vector. Example: vect.pop_back(); The statement above removes the last element of vect, thus reducing its size by 1.
  110. 110. 110 Starting Out with C++, 3rd Edition Summary of vector Member Functions push_back(value) Stores a value in the last element of the vector. If the vector is full or empty, a new element is created. Example: vect.push_back(7); The statement above stores 7 in the last element of vect. reverse() Reverses the order of the elements in the vector (the last element becomes the first element, and the first element becomes the last element.) Example: vect.reverse(); The statement above reverses the order of the element in vect. resize(elements, value) Resizes a vector by elements elements. Each of the new elements is initialized with the value in value. Example: vect.resize(5, 1); The statement above increases the size of vect by 5 elements. The 5 new elements are initialized to the value 1.
  111. 111. 111 Starting Out with C++, 3rd Edition Summary of vector Member Functions swap(vector2) Swaps the contents of the vector with the contents of vector2. Example: vect1.swap(vect2); The statement above swaps the contents of vect1 and vect2.

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