程序实践系列之利用2D数组的GradeBook类

介绍类GradeBook,使用一个二维数组存储学生在多次考试所得的成绩.在一个学期中,学生很可能参加多次考试,老师也可能希望分析一个学生或整个班级在整个学期所获得成绩.即:在GradeBook二维数组中存储学生成绩.程序如下所示:

二维数组存储学生成绩类GradeBook的定义

//Definiton of class Gradebook that uses a two-dimesion array to store test grades

#include <string> //program uses C++ Standard Library string class
using namespace std;

#ifndef GRADEBOOK_H
#define GRADEBOOK_H

//GradeBook class definition
class GradeBook {
public:
	//constants
	static const int students =10; //number of students
	static const int tests = 3; // number of tests

	//constructor inititalizes cousre name and array of grades
	GradeBook(string, const int [][ tests]);

	void  setCourseName( string);	// function to set the course name
	string getCourseName();	// function to retrieve the course name
	void displayMessage(); // display a welcome message
	void processGrades();	// perform various operations on the grade data
	int getMinimum(); //find the minimum grade in the grade book
	int getMaximum(); //find the maximum grade in the grade book
	double getAverage (const int[] , const int); // get student's average
	void outputBarChart(); // output bar char of grade distriudbution
	void outputGrades(); // output the constanets of the grades array
private:
	string courseName ; // course name for this grade book
	int grades[students][tests]; // two-dimensional array of grades
}; // end class

#endif //

操作二维数组的GradeBook类成员函数的定义

// Member-function definitions for class GradeBook that
// uses a two-dimensional array to store grades.
#include <iostream>
using std::cout;
using std::cin;
using std::endl;
using std::fixed;        

#include <iomanip> // parameterized stream manipulators
using std::setprecision; // sets numeric output precision
using std::setw; // sets field width

// include definition of class GradeBook from GradeBook.h
#include "GradeBook.h"

// two-argument constructor initializes courseName and grades array
GradeBook::GradeBook( string name, const int gradesArray[][ tests ] )
{
   setCourseName( name ); // initialize courseName

   // copy grades from gradeArray to grades
   for ( int student = 0; student < students; student++ )

      for ( int test = 0; test < tests; test++ )
         grades[ student ][ test ] = gradesArray[ student ][ test ];
} // end two-argument GradeBook constructor

// function to set the course name
void GradeBook::setCourseName( string name )
{
   courseName = name; // store the course name
} // end function setCourseName

// function to retrieve the course name
string GradeBook::getCourseName()
{
   return courseName;
} // end function getCourseName

// display a welcome message to the GradeBook user
void GradeBook::displayMessage()
{
   // this statement calls getCourseName to get the name of the course this GradeBook represents
   cout << "Welcome to the grade book for\n" << getCourseName() << "!" << endl;
} // end function displayMessage

// perform various operations on the data
void GradeBook::processGrades()
{
   // output grades array
   outputGrades();

   // call functions getMinimum and getMaximum
   cout << "\nLowest grade in the grade book is " << getMinimum() 
      << "\nHighest grade in the grade book is " << getMaximum() << endl;

   outputBarChart();// output grade distribution chart of all grades on all tests outputBarChart();
} // end function processGrades

// find minimum grade
int GradeBook::getMinimum()
{
   int lowGrade = 100; // assume lowest grade is 100

   for ( int student = 0; student < students; student++ ) // loop through rows of grades array
   {
      for ( int test = 0; test < tests; test++ ) // loop through columns of current row
      {
         if ( grades[ student ][ test ] < lowGrade ) // if current grade less than lowGrade, assign it to lowGrade
            lowGrade = grades[ student ][ test ]; // new lowest grade
      } // end inner for
   } // end outer for

   return lowGrade; // return lowest grade
} // end function getMinimum

// find maximum grade
int GradeBook::getMaximum()
{
   int highGrade = 0; // assume highest grade is 0

   // loop through rows of grades array
   for ( int student = 0; student < students; student++ )
   {
      // loop through columns of current row
      for ( int test = 0; test < tests; test++ )
      {
         // if current grade greater than lowGrade, assign it to highGrade
         if ( grades[ student ][ test ] > highGrade )
            highGrade = grades[ student ][ test ]; // new highest grade
      } // end inner for
   } // end outer for

   return highGrade; // return highest grade
} // end function getMaximum     

// determine average grade for particular set of grades
double GradeBook::getAverage( const int setOfGrades[], const int grades )
{
   int total = 0; // initialize total

   // sum grades in array
   for ( int grade = 0; grade < grades; grade++ )
      total += setOfGrades[ grade ];

   return static_cast< double >( total ) / grades; // return average of grades
} // end function getAverage

// output bar chart displaying grade distribution
void GradeBook::outputBarChart()
{
   cout << "\nOverall grade distribution:" << endl;

   // stores frequency of grades in each range of 10 grades
   const int frequencySize = 11;
   int frequency[ frequencySize ] = { 0 };

   // for each grade, increment the appropriate frequency
   for ( int student = 0; student < students; student++ )

      for ( int test = 0; test < tests; test++ )
         ++frequency[ grades[ student ][ test ] / 10 ];

   // for each grade frequency, print bar in chart
   for ( int count = 0; count < frequencySize; count++ ) 
   {
      // output bar label ("0-9:", ..., "90-99:", "100:" )
      if ( count == 0 )
         cout << "  0-9: ";
      else if ( count == 10 )
         cout << "  100: ";
      else
         cout << count * 10 << "-" << ( count * 10 ) + 9 << ": ";
      
      // print bar of asterisks
      for ( int stars = 0; stars < frequency[ count ]; stars++ ) 
         cout << '*';

      cout << endl; // start a new line of output
   } // end outer for
} // end function outputBarChart

// output the contents of the grades array
void GradeBook::outputGrades()
{
   cout << "\nThe grades are:\n\n";
   cout << "            "; // align column heads

   // create a column heading for each of the tests
   for ( int test = 0; test < tests; test++ )
      cout << "Test " << test + 1 << "  ";

   cout << "Average" << endl; // student average column heading

   // create rows/columns of text representing array grades
   for ( int student = 0; student < students; student++ )
   {
      cout << "Student " << setw( 2 ) << student + 1;

      // output student's grades
      for ( int test = 0; test < tests; test++ )
         cout << setw( 8 ) << grades[ student ][ test ];

      // call member function getAverage to calculate student's average;
      // pass row of grades and the value of tests as the arguments
      double average = getAverage( grades[ student ], tests );
      cout << setw( 9 ) << setprecision( 2 ) << fixed << average << endl;
   } // end outer for
} // end function outputGrades

测试GradeBook类

// TestMain.cpp
// Creates GradeBook object using a two-dimensional array of grades.

#include "GradeBook.h" // GradeBook class definition

// function main begins program execution
int main()
{
   // two-dimensional array of student grades
   int gradesArray[ GradeBook::students ][ GradeBook::tests ] = 
      { { 87, 96, 70 },{ 68, 87, 90 },
        { 94, 100, 90 },{ 100, 81, 82 },
        { 83, 65, 85 },{ 78, 87, 65 },
        { 85, 75, 83 },{ 91, 94, 100 },
        { 76, 72, 84 },{ 87, 93, 73 } };
               
   GradeBook myGradeBook( 
     "C++ Programming Practice", gradesArray );
   myGradeBook.displayMessage();
   myGradeBook.processGrades(); 
   return 0; // indicates successful termination
} // end main

测试输出结果

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