Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Chapter 7 Arrays.

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 5 Introduction to Arrays An array is used to process a collection of data of the same type Examples: A list of names A list of temperatures Why do we need arrays? Imagine keeping track of 5 test scores, or 100, or 1000 in memory How would you name all the variables? How would you process each of the variables?

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 6 Declaring an Array An array, named score, containing five variables of type int can be declared as int score[ 5 ]; This is like declaring 5 variables of type int: score[0], score[1], …, score[4] The value in brackets is called A subscript An index

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 7 The Array Variables The variables making up the array are referred to as Indexed variables Subscripted variables Elements of the array The number of indexed variables in an array is the declared size, or size, of the array The largest index is one less than the size The first index value is zero

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 8 Array Variable Types An array can have indexed variables of any type All indexed variables in an array are of the same type This is the base type of the array An indexed variable can be used anywhere an ordinary variable of the base type is used

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 9 Using [ ] With Arrays In an array declaration, [ ]'s enclose the size of the array such as this array of 5 integers: int score [5]; When referring to one of the indexed variables, the [ ]'s enclose a number identifying one of the indexed variables score[3] is one of the indexed variables The value in the [ ]'s can be any expression that evaluates to one of the integers 0 to (size -1)

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 10 Indexed Variable Assignment To assign a value to an indexed variable, use the assignment operator: int n = 2; score[n + 1] = 99; In this example, variable score[3] is assigned 99

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Print array using Cin #include //decreasing. for (i=5;i>=0;i--) main() { int i,first_arry[6]; for (i=0;i<6;i++) cin>> first_arry[i] ; cout<<"the Content of array is.\n"; for (i=0;i<6;i++) cout<< first_arry[i]<<"\t"; system("pause"); return 0; } Slide 7- 14

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Adding item in array #include main() { int i,array1[5],sum=0; for (i=0;i<5;i++) cin>> array1[i] ; for (i=0;i<5;i++) sum=sum+array1[i]; cout<< "sum of array item="<<sum; system("pause"); return 0; } Slide 7- 15

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Find max number #include main() { int i,array1[7],max; for (i=0;i<7;i++) cin>> array1[i] ; max=array1[0]; for (i=0;i<7;i++) if (array1[i] > max ) max=array1[i]; cout<< "max number in array1 is="<<max;} Slide 7- 17

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Multiply by *2 array1[i]=2* array1[i]; //Multiply by *2 array1[i]= array1[i] /4; //divided by 4 #include main() { int i,array1[5]={10,15,30,32,21}; for (i=0;i<5;i++) { array1[i]= array1[i]+5; cout<< array1[i]<<"\t";} } Slide 7- 18

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Adding array of five item #include main() { int i,array1[5],sum=0; for (i=0;i<5;i++) cin>> array1[i] ; for (i=0;i<5;i++) sum=sum+array1[i]; cout<< "sum of array item="<<sum;} Slide 7- 20

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. //Inter 7 item find maximum number #include main() { int i,array1[7],max; for (i=0;i<7;i++) cin>> array1[i] ; max=array1[0]; for (i=0;i<7;i++) if (array1[i] > max ) max=array1[i]; cout<< "max number in array1 is="<<max;} Slide 7- 21

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Adding number to each array[i] #include main() { int i,array1[5]={10,15,30,32,21}; for (i=0;i<5;i++) { array1[i]= array1[i]+5; cout<< array1[i]<<"\t";} } Slide 7- 22

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Inter the number and sort by smaller to bigger #include int main() { int array[5],i,j; int item=0; cout<<"Here is the Array before sorted enter it\n"; for (i=0;i<5;i++) cin>>array[i] ; for ( i=0;i<5-1;i++) for ( j=i; j<5;j++) if (array[j] <array[i]) { item =array[j]; array[j]=array[i]; array[i]= item ; } cout<<"Here is the Array after sorted\n"; for (i=0;i<5;i++) cout<<array[i]<<"\n"; system("pause");} Slide 7- 23

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Array of odd and array of even #include main() {int count_a, count_b=0, count_c=0,a[5],b[5], c[5]; for( count_a=0; count_a<5; count_a++) cin>>a[ count_a]; for( count_a=0; count_a<5; count_a++) if ( a[ count_a] %2==0) {b[ count_b ]=a[count_a]; count_b= count_b+1;} else {c[ count_c ]=a[count_a]; count_c= count_c+1;} cout<<"items in array b is\n"; for( count_a=0; count_a< count_b; count_a++) cout<< b[ count_a ]<<"\t"; cout<<"\nitems in array c is\n"; for( count_a=0; count_a< count_c; count_a++) cout<< c[ count_a ]<<"\t"; system("pause");} Slide 7- 24

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. To declare an array in C++, the programmer specifies the type of the elements and the number of elements required by an array as follows: type arrayName [ arraySize ]; double balance[10]; type arrayName [ arraySize ]; This is called a single-dimension array. The arraySize must be an integer constant greater than zero and type can be any valid C++ data type. For example, to declare a 10-element array called balance of type double, use this statement:

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Initializing Arrays Initializing Arrays: You can initialize C++ array elements either one by one or using a single statement as follows: double balance[5] = {1000.0, 2.0, 3.4, 17.0, 50.0}; The number of values between braces { } can not be larger than the number of elements that we declare for the array between square brackets [ ]. Following is an example to assign a single element of the array: If you omit the size of the array, an array just big enough to hold the initialization is created. Therefore, if you write: double balance[] = {1000.0, 2.0, 3.4, 17.0, 50.0};

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. balance[4] = 50.0; The above statement assigns element number 5th in the array a value of 50.0. Array with 4th index will be 5th i.e.. last element because all arrays have 0 as the index of their first element which is also called base index. Following is the pictorial representation of the same array we discussed above:

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Two-Dimensional Arrays type name[size1][size2]...[sizeN]; For example, the following declaration creates a three dimensional 5. 10. 4 integer array: int threedim[5][10][4]; type arrayName [ x ][ y ]; // two dimensional

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. initializing Two-Dimensional Arrays: Multi dimensioned arrays may be initialized by specifying bracketed values for each row. Following is an array with 3 rows and each row have 4 columns. int a[3][4] = { {0, 1, 2, 3}, /* initializers for row indexed by 0 */ {4, 5, 6, 7}, /* initializers for row indexed by 1 */ {8, 9, 10, 11} /* initializers for row indexed by 2 */ };

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. #include using namespace std; int main () { // an array with 5 rows and 2 columns. int a[5][2] = { {0,0}, {1,2}, {2,4}, {3,6},{4,8}}; // output each array element's value for ( int i = 0; i < 5; i++ ) for ( int j = 0; j < 2; j++ ) { cout << "a[" << i << "][" << j << "]: "; cout << a[i][j]<< endl; } return 0; }

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Initialization of Two-Dimensional Array An two-dimensional array can be initialized along with declaration. For two- dimensional array initialization, elements of each row are enclosed within curly braces and separated by commas. All rows are enclosed within curly braces. int A[4][3] = {{22, 23, 10}, {15, 25, 13}, {20, 74, 67}, {11, 18, 14}}; cout<<A[1][2]; //print an array element A[1][2]=13; // assign value to an array element cin>>A[1][2]; //input element

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Two-Dimensional Array cout<<A[1][2]; //print an array element A[1][2]=13; // assign value to an array element cin>>A[1][2]; //input element Using Loop to input an Two-Dimensional Array from user int mat[3][5], row, col ; for (row = 0; row < 3; row++) for (col = 0; col < 5; col++) cin >> mat[row][col];

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. 33 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 void main(void) { char letters[10] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J'}; cout << "Character" << "\t" << "ASCII Code\n"; cout << "--------" << "\t" << "----------\n"; for (int count = 0; count < 10; count++) { cout << letters[count] << "\t\t"; cout << int(letters[count]) << endl; }

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. 34 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};

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. 35 Program 7-8 // This program has a partially initialized array. #include 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; }

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. 37 Implicit (hidden) 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};

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. 38 Initializing With Strings When initializing a character array with a string, simply enclose the string in quotation marks: char name[] = “Warren”;

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. 40 Program 7-9 // This program displays the contents of two char arrays. #include void main(void) { char name1[] = "Holly"; char name2[] = {'W', 'a', 'r', 'r', 'e', 'n', '\0'}; cout << name1 << endl; cout << name2 << endl; }

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. 43 Program 7-10 // This program stores, in an array, the hours worked by 5 // employees who all make the same hourly wage. #include void main(void) { int hours[5]; float payRate; cout << "Enter the hours worked by 5 employees who all\n"; cout << "earn the same hourly rate.\n"; for (int index = 0; index < 5; index++) { cout << "Employee #" << (index + 1) << ": "; cin >> hours[index]; }

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. 44 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; }

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Multi array #include main() { 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"; } system("pause"); }

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. String in array #include using namespace std; int main () { char greeting[6] = {'H', 'e', 'l', 'l', 'o', '\0'}; cout << "Greeting message: "; cout << greeting << endl; return 0; }

#include using namespace std; int main () { char str1[10] = "Hello"; char str2[10] = "World"; char str3[10]; int len ; // copy str1 into str3 strcpy( str3, str1); cout << "strcpy( str3, str1) : " << str3 << endl; // concatenates str1 and str2 strcat( str1, str2); cout << "strcat( str1, str2): " << str1 << endl; // total lenghth of str1 after concatenation len = strlen(str1); cout << "strlen(str1) : " << len << endl; return 0; }

Declaring Arrays: To declare an array in C++, the programmer specifies the type of the elements and the number of elements required by an array as follows: type arrayName [ arraySize ]; This is called a single-dimension array. The arraySize must be an integer constant greater than zero and type can be any valid C++ data type. For example, to declare a 10-element array called balance of type double, use this statement: double balance[10]; Initializing Arrays: You can initialize C++ array elements either one by one or using a single statement as follows: double balance[5] = {1000.0, 2.0, 3.4, 17.0, 50.0}; The number of values between braces { } can not be larger than the number of elements that we declare for the array between square brackets [ ]. Following is an example to assign a single element of the array: If you omit the size of the array, an array just big enough to hold the initialization is created. Therefore, if you write: double balance[] = {1000.0, 2.0, 3.4, 17.0, 50.0};

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. for-loops are commonly used to step through arrays Example: for (i = 0; i < 5; i++) { cout << score[i] << " off by " << (max – score[i]) << endl; } could display the difference between each score and the maximum score stored in an array Slide 7- 54 First index is 0 Display 7.1 Loops And Arrays Last index is (size – 1)

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 55 Constants and Arrays Use constants to declare the size of an array Using a constant allows your code to be easily altered for use on a smaller or larger set of data Example: const int NUMBER_OF_STUDENTS = 50; int score[NUMBER_OF_STUDENTS]; … for ( i = 0; i < NUMBER_OF_STUDENTS; i++) cout << score[i] << " off by " << (max – score[i]) << endl; Only the value of the constant must be changed to make this code work for any number of students

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 56 Variables and Declarations Most compilers do not allow the use of a variable to declare the size of an array Example: cout > number; int score[number]; This code is illegal on many compilers

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 57 Array Declaration Syntax To declare an array, use the syntax: Type_Name Array_Name[Declared_Size]; Type_Name can be any type Declared_Size can be a constant to make your program more versatile Once declared, the array consists of the indexed variables: Array_Name[0] to Array_Name[Declared_Size -1]

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 58 Computer Memory Computer memory consists of numbered locations called bytes A byte's number is its address A simple variable is stored in consecutive bytes The number of bytes depends on the variable's type A variable's address is the address of its first byte

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Declaring the array int a[6] Reserves memory for six variables of type int The variables are stored one after another The address of a[0] is remembered The addresses of the other indexed variables is not remembered To determine the address of a[3] Start at a[0] Count past enough memory for three integers to find a[3] Slide 7- 59 Display 7.2 Arrays and Memory

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 60 Array Index Out of Range A common error is using a nonexistent index Index values for int a[6] are the values 0 through 5 An index value not allowed by the array declaration is out of range Using an out of range index value doe not produce an error message!

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 61 Out of Range Problems If an array is declared as: int a[6]; and an integer is declared as: int i = 7; Executing the statement a[i] = 238; causes… The computer to calculate the address of the illegal a[7] (This address could be where some other variable is stored) The value 238 is stored at the address calculated for a[7] No warning is given!

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 62 Initializing Arrays To initialize an array when it is declared The values for the indexed variables are enclosed in braces and separated by commas Example: int children[3] = { 2, 12, 1 }; Is equivalent to: int children[3]; children[0] = 2; children[1] = 12; children[2] = 1;

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 63 Default Values If too few values are listed in an initialization statement The listed values are used to initialize the first of the indexed variables The remaining indexed variables are initialized to a zero of the base type Example: int a[10] = {5, 5}; initializes a[0] and a[1] to 5 and a[2] through a[9] to 0

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 64 Un-initialized Arrays If no values are listed in the array declaration, some compilers will initialize each variable to a zero of the base type DO NOT DEPEND ON THIS!

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 65 Section 7.1 Conclusion Can you Describe the difference between a[4] and int a[5]? Show the output of char symbol[3] = {'a', 'b', 'c'}; for (int index = 0; index < 3; index++) cout << symbol[index];

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Indexed variables can be arguments to functions Example: If a program contains these declarations: int i, n, a[10]; void my_function(int n); Variables a[0] through a[9] are of type int, making these calls legal: my_function( a[ 0 ] ); my_function( a[ 3 ] ); my_function( a[ i ] ); Slide 7- 67 Display 7.3 Arrays in Functions

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 68 Arrays as Function Arguments A formal parameter can be for an entire array Such a parameter is called an array parameter It is not a call-by-value parameter It is not a call-by-reference parameter Array parameters behave much like call-by- reference parameters

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 69 Array Parameter Declaration An array parameter is indicated using empty brackets in the parameter list such as void fill_up(int a[ ], int size);

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. If function fill_up is declared in this way: void fill_up(int a[ ], int size); and array score is declared this way: int score[5], number_of_scores; fill_up is called in this way: fill_up(score, number_of_scores); Slide 7- 70 Display 7.4 Function Calls With Arrays

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 71 Function Call Details A formal parameter is identified as an array parameter by the [ ]'s with no index expression void fill_up(int a[ ], int size); An array argument does not use the [ ]'s fill_up(score, number_of_scores);

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 72 Array Formal Parameters An array formal parameter is a placeholder for the argument When an array is an argument in a function call, an action performed on the array parameter is performed on the array argument The values of the indexed variables can be changed by the function

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 73 Array Argument Details What does the computer know about an array? The base type The address of the first indexed variable The number of indexed variables What does a function know about an array argument? The base type The address of the first indexed variable

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 74 Array Parameter Considerations Because a function does not know the size of an array argument… The programmer should include a formal parameter that specifies the size of the array The function can process arrays of various sizes Function fill_up from Display 7.4 can be used to fill an array of any size: fill_up(score, 5); fill_up(time, 10);

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 75 const Modifier Array parameters allow a function to change the values stored in the array argument If a function should not change the values of the array argument, use the modifier const An array parameter modified with const is a constant array parameter Example: void show_the_world(const int a[ ], int size);

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 76 Using const With Arrays If const is used to modify an array parameter: const is used in both the function declaration and definition to modify the array parameter The compiler will issue an error if you write code that changes the values stored in the array parameter

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 77 Function Calls and const If a function with a constant array parameter calls another function using the const array parameter as an argument… The called function must use a constant array parameter as a placeholder for the array The compiler will issue an error if a function is called that does not have a const array parameter to accept the array argument

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 78 const Parameters Example double compute_average(int a[ ], int size); void show_difference(const int a[ ], int size) { double average = compute_average(a, size); … } compute_average has no constant array parameter This code generates an error message because compute_average could change the array parameter

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 79 Returning An Array Recall that functions can return a value of type int, double, char, …, or a class type Functions cannot return arrays We learn later how to return a pointer to an array

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 80 Case Study: Production Graph Problem Definition: We are writing a program for the Apex Plastic Spoon Company The program will display a bar graph showing the production of each of four plants for a week Each plant has separate records for each department Input is entered plant by plant Output shows one asterisk for each 1000 units, and production is rounded to the nearest 1,000 units

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 81 Analysis of The Problem Use an array named production to hold total production of each plant Production for plant n is stored in production[n-1] Program must scale production to nearest 1,000 units to display asterisks in the bar

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 82 Production Graph Sub-Tasks Analysis leads to the following sub-tasks input_data: Read input for each plant Set production [plant_number -1] to the total production for plant number n scale: For each plant, change production[plant_number] to the correct number of asterisks graph: Output the bar graph

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. The entire array will be an argument for the functions we write to perform the subtasks We will also include a formal parameter for the size The size of the array is equal to the number of plants We will use a constant for the number of plants The function declarations and main function for the production graph program are found in Slide 7- 83 Display 7.5 More Analysis Details

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 84 Algorithm Design: input_data We must read all departments' data for each plant and add them to produce a plant's total Algorithm for input_data: for plant_number is 1, 2, …, last_plant_number do the following Read all the data for plant number plant_number Sum the numbers Set production[plant_number – 1] to the total

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 85 Coding input_data The algorithm can be translated to C++ as: void input_data(int a [ ], int last_plant_number) { using namespace std; for (int plant_number = 1; plant_number <= last_plant_number; plant_number++) { cout << endl; << "Enter production for plant" << plant_number << endl; get_total( a[plant_number -1] ); } }

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Each function should be tested in a program in which it is the only untested function Because input_data calls get_total, get_total is tested first Once tested, get_total can be used to test input_data Slide 7- 86 Display 7.6 (1) Display 7.6 (2) Display 7.6 (3) Testing input_data

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 87 Test Data for input_data Remember that input_data should be tested With a plant that contains no production figures With a plant having only one production figure With a plant having more than one figure With zero and non-zero production figures

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 88 Algorithm for scale scale changes the value of the indexed variable to show the whole number of asterisks to print Scale is called using scale (production, NUMBER_OF_PLANTS); and its algorithm is for (int index = 0; index < size; index++) Divide the value of a[index] by 1,000 and round the result to the nearest integer

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 89 Why not 1000? Coding scale The code for scale, below, uses a function named round that must be defined as well void scale(int a[ ], int size) { for (int index = 0; index < size; index++) a[index] = round (a[index] / 1000.0); }

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 90 Function floor Function round, called by scale, uses the floor function from the cmath library The floor function returns the first whole number less than its argument: floor (3.4) returns 3 floor (3.9) returns 3 Adding 0.5 to the argument for floor is how round performs its task floor (3.4 + 0.5) returns 3 floor (3.9 + 0.5) returns 4

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. To test scale First test round Scale should be tested with arguments that Are 0 Round up Round down Slide 7- 91 Display 7.7 (1) Display 7.7 (2) Testing scale

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. The design of graph is quite straightforward and not included here The complete program to produce the bar graph is found in Slide 7- 92 Display 7.8 (1) Display 7.8 (2) Display 7.8 (3) Function graph

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 93 Section 7.2 Conclusion Can you Write a function definition for a function called one_more, which has a formal parameter for an array of integers and increases the value of each array element by one. Are other formal parameters needed?

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 95 Programming With Arrays The size needed for an array is changeable Often varies from one run of a program to another Is often not known when the program is written A common solution to the size problem Declare the array size to be the largest that could be needed Decide how to deal with partially filled arrays

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. When using arrays that are partially filled Functions dealing with the array may not need to know the declared size of the array, only how many elements are stored in the array A parameter, number_used, may be sufficient to ensure that referenced index values are legal A function such as fill_array in Display 7.9 needs to know the declared size of the array Slide 7- 96 Display 7.9 (1)Display 7.9 (2)Display 7.9 (3) Partially Filled Arrays

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 97 Constants as Arguments When function fill_array (Display 7.9) is called, MAX_NUMBER_SCORES is used as an argument Can't MAX_NUMBER_SCORES be used directly without making it an argument? Using MAX_NUMBER_SCORES as an argument makes it clear that fill_array requires the array's declared size This makes fill_array easier to be used in other programs

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 98 Searching Arrays A sequential search is one way to search an array for a given value Look at each element from first to last to see if the target value is equal to any of the array elements The index of the target value can be returned to indicate where the value was found in the array A value of -1 can be returned if the value was not found

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. The search function of Display 7.10… Uses a while loop to compare array elements to the target value Sets a variable of type bool to true if the target value is found, ending the loop Checks the boolean variable when the loop ends to see if the target value was found Returns the index of the target value if found, otherwise returns -1 Slide 7- 99 Display 7.10 (1)Display 7.10 (2) The search Function

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 100 Program Example: Sorting an Array Sorting a list of values is very common task Create an alphabetical listing Create a list of values in ascending order Create a list of values in descending order Many sorting algorithms exist Some are very efficient Some are easier to understand

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 101 Program Example: The Selection Sort Algorithm When the sort is complete, the elements of the array are ordered such that a[0] < a[1] < … < a [ number_used -1] This leads to an outline of an algorithm: for (int index = 0; index < number_used; index++) place the indexth smallest element in a[index]

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. One array is sufficient to do our sorting Search for the smallest value in the array Place this value in a[0], and place the value that was in a[0] in the location where the smallest was found Starting at a[1], find the smallest remaining value swap it with the value currently in a[1] Starting at a[2], continue the process until the array is sorted Slide 7- 102 Display 7.11Display 7.12 (1-2) Program Example: Sort Algorithm Development

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 103 Section 7.3 Conclusion Can you Write a program that will read up to 10 letters into an array and write the letters back to the screen in the reverse order? abcd should be output as dcba Use a period as a sentinel value to mark the end of input

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 105 Multi-Dimensional Arrays C++ allows arrays with multiple index values char page [30] [100]; declares an array of characters named page page has two index values: The first ranges from 0 to 29 The second ranges from 0 to 99 Each index in enclosed in its own brackets Page can be visualized as an array of 30 rows and 100 columns

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 106 Index Values of page The indexed variables for array page are page[0][0], page[0][1], …, page[0][99] page[1][0], page[1][1], …, page[1][99] … page[29][0], page[29][1], …, page[29][99] page is actually an array of size 30 page's base type is an array of 100 characters

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 107 Multidimensional Array Parameters Recall that the size of an array is not needed when declaring a formal parameter: void display_line(const char a[ ], int size); The base type of a multi-dimensional array must be completely specified in the parameter declaration void display_page(const char page[ ] [100], int size_dimension_1);

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 108 Program Example: Grading Program Grade records for a class can be stored in a two-dimensional array For a class with 4 students and 3 quizzes the array could be declared as int grade[4][3]; The first array index refers to the number of a student The second array index refers to a quiz number Since student and quiz numbers start with one, we subtract one to obtain the correct index

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. The grading program uses one-dimensional arrays to store… Each student's average score Each quiz's average score The functions that calculate these averages use global constants for the size of the arrays This was done because the functions seem to be particular to this program Slide 7- 109 Display 7.13 (1-3) Display 7.14 Display 7.15 Grading Program: average scores

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Slide 7- 110 Section 7.5 Conclusion Can you Write code that will fill the array a(declared below) with numbers typed at the keyboard? The numbers will be input fiver per line, on four lines. int a[4][5];

Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Chapter 7 Arrays.

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Copyright © 2008 Pearson Addison-Wesley. All rights reserved. Chapter 7 Arrays.

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