Deitel Series Page How To Program Series

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2 Deitel Series Page How To Program Series Android How to Program C How to Program, 7/E C++ How to Program, 9/E C++ How to Program, Late Objects Version, 7/E Java How to Program, 9/E Java How to Program, Late Objects Version, 8/E Internet & World Wide Web How to Program, 5/E Visual Basic 2012 How to Program Visual C# 2012 How to Program, 3/E Visual C How to Program, 2/E Small Java How to Program, 6/E Small C++ How to Program, 5/E Simply Series Simply C++: An App-Driven Tutorial Approach Simply Java Programming: An App-Driven Tutorial Approach Simply Visual Basic 2010, 4/E: An App-Driven Tutorial Approach CourseSmart Web Books C++ How to Program, 7/E, 8/E & 8/E Simply C++: An App-Driven Tutorial Approach Java How to Program, 7/E, 8/E & 9/E Simply Visual Basic 2010: An App-Driven Approach, 4/E Visual Basic 2012 How to Program Visual Basic 2010 How to Program Visual C# 2012 How to Program, 5/E Visual C# 2010 How to Program, 4/E Deitel Developer Series C++ for Programmers, 2/E Android for Programmers: An App-Driven Approach C# 2010 for Programmers, 3/E Dive Into ios 6: An App-Driven Approach ios 6 for Programmers: An App-Driven Approach Java for Programmers, 2/E JavaScript for Programmers LiveLessons Video Learning Products Android App Development Fundamentals C++ Fundamentals C# Fundamentals ios 6 App Development Fundamentals Java Fundamentals JavaScript Fundamentals Visual Basic Fundamentals To receive updates on Deitel publications, Resource Centers, training courses, partner offers and more, please register for the free Deitel Buzz Online newsletter at: and join the Deitel communities on Facebook facebook.com/deitelfan and Google+ gplus.to/deitel To communicate with the authors, send to: deitel@deitel.com For information on government and corporate Dive-Into Series on-site seminars offered by Deitel & Associates, Inc. worldwide, visit: or write to deitel@deitel.com For continuing updates on Prentice Hall/Deitel publications visit: Visit the Deitel Resource Centers that will help you master programming languages, software development, Android and iphone/ipad app development, and Internet- and web-related topics:

3 7.4 Examples Using arrays const int x = 7; // initialized constant variable 9 10 cout << "The value of constant variable x is: " << x << endl; 11 } // end main The value of constant variable x is: 7 Fig. 7.6 Using a properly initialized constant variable. (Part 2 of 2.) 1 // Fig. 7.7: fig07_07.cpp 2 // A const variable must be initialized. 3 4 int main() 5 { 6 const int x; // Error: x must be initialized 7 8 x = 7; // Error: cannot modify a const variable 9 } // end main Microsoft Visual C++ compiler error message: error C2734: 'x' : const object must be initialized if not extern error C3892: 'x' : you cannot assign to a variable that is const GNU C++ compiler error message: fig07_07.cpp:6:14: error: uninitialized const x [-fpermissive] fig07_07.cpp:8:8: error: assignment of read-only variable x LLVM compiler error message: Default initialization of an object of const type 'const int' Fig. 7.7 A const variable must be initialized. In Fig. 7.7, the compilation error produced by Microsoft Visual C++ refers to the int variable x as a const object. The C++ standard defines an object as any region of storage. Like class objects, fundamental-type variables also occupy space in memory, so they re often referred to as objects. Constant variables can be placed anywhere a constant expression is expected. In Fig. 7.5, constant variable arraysize specifies the size of array s in line 13. Good Programming Practice 7.1 Defining the size of an array as a constant variable instead of a literal constant makes programs clearer. This technique eliminates so-called magic numbers numeric values that are not explained. Using a constant variable allows you to provide a name for a literal constant and can help explain the purpose of the value in the program.

4 320 Chapter 7 Class Templates array and vector; Catching Exceptions Summing the Elements of an array Often, the elements of an array represent a series of values to be used in a calculation. For example, if the elements of an array represent exam grades, a professor may wish to total the elements of the array and use that sum to calculate the class average for the exam. The program in Fig. 7.8 sums the values contained in the four-element integer array a. The program declares, creates and initializes the array in line 10. The for statement (lines 14 15) performs the calculations. The values being supplied as initializers for array a also could be read into the program from the user at the keyboard, or from a file on disk (see Chapter 14, File Processing). For example, the for statement for ( size_t j = 0; j < a.size(); ++j ) cin >> a[ j ]; reads one value at a time from the keyboard and stores the value in element a[j]. 1 // Fig. 7.8: fig07_08.cpp 2 // Compute the sum of the elements of an array. 4 #include <array> 5 using namespace std; 6 7 int main() 8 { 9 const size_t arraysize = 4; // specifies size of array 10 array< int, arraysize > a = { 10, 20, 30, 40 }; 11 int total = 0; // sum contents of array a for ( size_t i = 0; i < a.size(); ++i ) total += a[ i ]; 17 cout << "Total of array elements: " << total << endl; 18 } // end main Total of array elements: 100 Fig. 7.8 Computing the sum of the elements of an array Using Bar Charts to Display array Data Graphically Many programs present data to users in a graphical manner. For example, numeric values are often displayed as bars in a bar chart. In such a chart, longer bars represent proportionally larger numeric values. One simple way to display numeric data graphically is with a bar chart that shows each numeric value as a bar of asterisks (*). Professors often like to examine grade distributions on an exam. A professor might graph the number of grades in each of several categories to visualize the grade distribution. Suppose the grades were 87, 68, 94, 100, 83, 78, 85, 91, 76 and 87. There was one grade of 100, two grades in the 90s, four grades in the 80s, two grades in the 70s, one grade in the 60s and no grades below 60. Our next program (Fig. 7.9) stores this data in an array of 11 elements, each corresponding to a grade category. For example, n[0] indicates the number of grades in the range 0 9, n[7] indicates the number of grades in the range and

5 7.4 Examples Using arrays // Fig. 7.9: fig07_09.cpp 2 // Bar chart printing program. 4 #include <iomanip> 5 #include <array> 6 using namespace std; 7 8 int main() 9 { 10 const size_t arraysize = 11; 11 array< unsigned int, arraysize > n = 12 { 0, 0, 0, 0, 0, 0, 1, 2, 4, 2, 1 }; cout << "Grade distribution:" << endl; // for each element of array n, output a bar of the chart 17 for ( size_t i = 0; i < n.size(); ++i ) 18 { 19 // output bar labels ("0-9:",..., "90-99:", "100:" ) 20 if ( 0 == i ) 21 cout << " 0-9: "; 22 else if ( 10 == i ) 23 cout << " 100: "; 24 else 25 cout << i * 10 << "-" << ( i * 10 ) + 9 << ": "; // print bar of asterisks 28 for ( unsigned int stars = 0; stars < n[ i ]; ++stars ) 29 cout << '*'; cout << endl; // start a new line of output 32 } // end outer for 33 } // end main Grade distribution: 0-9: 10-19: 20-29: 30-39: 40-49: 50-59: 60-69: * 70-79: ** 80-89: **** 90-99: ** 100: * Fig. 7.9 Bar chart printing program. n[10] indicates the number of grades of 100. The GradeBook versions in Figs and Figs contain code that calculates these grade frequencies based on a set of grades. For now, we manually create the array by looking at the set of grades. The program reads the numbers from the array and graphs the information as a bar chart, displaying each grade range followed by a bar of asterisks indicating the number of

6 322 Chapter 7 Class Templates array and vector; Catching Exceptions grades in that range. To label each bar, lines output a grade range (e.g., "70-79: ") based on the current value of counter variable i. The nested for statement (lines 28 29) outputs the bars. Note the loop-continuation condition in line 28 (stars < n[i]). Each time the program reaches the inner for, the loop counts from 0 up to n[i], thus using a value in array n to determine the number of asterisks to display. In this example, n[0] n[5] contain zeros because no students received a grade below 60. Thus, the program displays no asterisks next to the first six grade ranges Using the Elements of an array as Counters Sometimes, programs use counter variables to summarize data, such as the results of a survey. In Fig. 6.9, we used separate counters in our die-rolling program to track the number of occurrences of each side of a die as the program rolled the die 6,000,000 times. An array version of this program is shown in Fig This version also uses the new C++11 random-number generation capabilities that were introduced in Section 6.9. Figure 7.10 uses the array frequency (line 18) to count the occurrences of each side of the die. The single statement in line 22 of this program replaces the switch statement in lines of Fig Line 22 uses a random value to determine which frequency element to 1 // Fig. 7.10: fig07_10.cpp 2 // Die-rolling program using an array instead of switch. 4 #include <iomanip> 5 #include <array> 6 #include <random> 7 #include <ctime> 8 using namespace std; 9 10 int main() 11 { 12 // use the default random-number generation engine to 13 // produce uniformly distributed pseudorandom int values from 1 to 6 14 default_random_engine engine( static_cast< unsigned int >( time(0) ) ); 15 uniform_int_distribution< unsigned int > randomint( 1, 6 ); const size_t arraysize = 7; // ignore element zero 18 array< unsigned int, arraysize > frequency = {}; // initialize to 0s // roll die 6,000,000 times; use die value as frequency index 21 for ( unsigned int roll = 1; roll <= ; ++roll ) frequency[ randomint( engine ) ]; 24 cout << "Face" << setw( 13 ) << "Frequency" << endl; // output each array element's value 27 for ( size_t face = 1; face < frequency.size(); ++face ) 28 cout << setw( 4 ) << face << setw( 13 ) << frequency[ face ] 29 << endl; 30 } // end main Fig Die-rolling program using an array instead of switch. (Part 1 of 2.)

7 7.4 Examples Using arrays 323 Face Frequency Fig Die-rolling program using an array instead of switch. (Part 2 of 2.) increment during each iteration of the loop. The calculation in line 22 produces a random subscript from 1 to 6, so array frequency must be large enough to store six counters. However, we use a seven-element array in which we ignore frequency[0] it s clearer to have the die face value 1 increment frequency[1] than frequency[0]. Thus, each face value is used directly as a subscript for array frequency. We also replace lines of Fig. 6.9 by looping through array frequency to output the results (Fig. 7.10, lines 27 29) Using arrays to Summarize Survey Results Our next example uses arrays to summarize the results of data collected in a survey. Consider the following problem statement: Twenty students were asked to rate on a scale of 1 to 5 the quality of the food in the student cafeteria, with 1 being awful and 5 being excellent. Place the 20 responses in an integer array and determine the frequency of each rating. This is a popular type of array-processing application (Fig. 7.11). We wish to summarize the number of responses of each type (that is, 1 5). The array responses (lines 15 16) is a 20-element integer array of the students responses to the survey. The array responses is declared const, as its values do not (and should not) change. We use a six-element array frequency (line 19) to count the number of occurrences of each response. Each element of the array is used as a counter for one of the survey responses and is initialized to zero. As in Fig. 7.10, we ignore frequency[0]. 1 // Fig. 7.11: fig07_11.cpp 2 // Poll analysis program. 4 #include <iomanip> 5 #include <array> 6 using namespace std; 7 8 int main() 9 { 10 // define array sizes 11 const size_t responsesize = 20; // size of array responses 12 const size_t frequencysize = 6; // size of array frequency // place survey responses in array responses 15 const array< unsigned int, responsesize > responses = 16 { 1, 2, 5, 4, 3, 5, 2, 1, 3, 1, 4, 3, 3, 3, 2, 3, 3, 2, 2, 5 }; Fig Poll analysis program. (Part 1 of 2.)