function parameter references

This is a discussion on function parameter references within the C++ Programming forums, part of the General Programming Boards category; Hello everyone, I am new to the boards and new to C++. I am reading Accelerated C++ and working through ...

  1. #1
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    Join Date
    Jun 2003
    Posts
    4

    function parameter references

    Hello everyone, I am new to the boards and new to C++. I am reading Accelerated C++ and working through Ch. 4. The program as it stands compiles fine, but it seems I dont completely understand what is going on when I reference another object. The program seems to read in data fine, but it is not ending up where I hoped. I have strayed a bit from the program covered in the book, I thought I might learn more that way. Thats what I get for thinking :/

    I am trying to get the data into the students vector. Any help would be much appreciated.

    Bob


    Code:
    //Grading Program
    //By Robert Lohaus
    //Chapter 4, Accelerated C++
    
    #include <algorithm>
    #include <iomanip>
    #include <ios>
    #include <stdexcept>
    #include <string>
    #include <vector>
    #include "Student_info.h"
    
    using std::cout;          using std::string;
    using std::endl;          using std::sort;
    using std::vector;        using std::domain_error;
    using std::setprecision;
    
    
    int main()
    {
        //presents a welcome message
    	cout << "Welcome Student Grading Program 0.0.1"
    		 << endl << endl;
    
    	//Global Objects
    	vector<Student_info> students;
    	string::size_type maxlen = 0;
    
    	//Reads Input into a vector
    	maxlen = read(students);
    
    	//alphabetize students
    	sort(students.begin(), students.end(), compare);
    
    	//write the names and grades
    	for (int i = 0; i != students.size(); ++i)
    	{
    		//write name padded on right to maxlen + 1
    		cout << students[i].name
    			 << string(maxlen + 1 - students[i].name.size(), ' ');
    	}
    
    
    
    
    	return 0;
    
    }
    #ifndef GAURD_Student_info
    #define GAURD_Student_info
    
    //Student_info.h
    #include <iostream>
    #include <vector>
    #include <string>
    
         struct Student_info
    	 {
    		 std::string name;
    		 double midterm, final;
    		 std::vector<double> homework;
         };
    
        
        //Function Definitions
    	 std::string::size_type read(std::vector<Student_info>&);
    	 int read_hw(std::vector<double>&);
    	 bool compare(const Student_info&, const Student_info&);
    
    	 double grade(const Student_info&);
    	 double grade(double, double, const std::vector<double>&);
    	 double grade(double, double, double);
    	 double median(const std::vector<double>&);
    
    
    #endif   
    
    #ifndef GAURD_Read
    #define GAURD_Read
    
    //Source for Read and related functions
    #include <iostream>
    #include <vector>
    #include <string>
    #include <stdexcept>
    #include <algorithm>
    #include "Student_info.h"
    
    using std::string;  using std::endl;
    using std::cout;    using std::vector;
    using std::cin;     
    
        
        
    
    	//Functions
        
        //read()
        //this function reads name,mid,final then passes
        //to read_hw to enter homework scores
        string::size_type read(vector<Student_info>& s)
    	{
    		Student_info record;
    		string end_cond;
    		string::size_type mname = 0;
    		string::size_type maxlen = 0;
    
    		//Reads the students name, midterm, final
    		cout << "Enter a student record? " << endl
    			 << "Enter 'Y' or 'N': ";
    		cin  >> end_cond;
    
    		while (end_cond == "y")
    		{
    			cin.clear();
    			cout << endl << "Student's Name: ";
    			cin  >> record.name;
    
    			cout << endl << "Student's Midterm: ";
                cin  >> record.midterm;
    
    			cout << endl << "Student's Final: ";
    			cin  >> record.final;
    
    			read_hw(record.homework);
    
                mname = record.name.size();
    			mname > maxlen ? maxlen = mname:
    
    			s.push_back(record);         
    						
    			
    			//This checks for more records
    			cout << endl << endl
    				 << endl << "Enter a student record? "
    			     << endl << "Enter 'Y' or 'N': ";
    		    cin  >> end_cond;
    
    		}
    
    	//returns the longest name for later printing
        return maxlen;
    
        }
    
    
    	//read_hw()
    	//this function reads homework scores and comes up with an average
    	int read_hw(vector<double>& hw)
    	{
    		string end_cond;
    	    double score;
            
    									
    		cout << endl << "Do you wish to enter another homework score? "
    			 << endl << "Press 'Y' or 'N': ";
            cin  >> end_cond;
    
    		while (end_cond == "y")
    		{ 
    		
    		    hw.clear();
    			cout << endl << "Enter a homework grade: ";
    			cin  >> score;
    			hw.push_back(score);
            
                cout << endl << "Do you wish to enter another homework score? "
    			     << endl << "Press 'Y' or 'N': ";
                cin  >> end_cond; 
    		} 
    		
    
    		return 0;
        }
    
         
    	//compare()
    	//this is used in the sort function
    	bool compare(const Student_info& x, const Student_info& y)
    	{
    		return x.name < y.name;
        }
    
    
    //grade functions
    
    	//grade()
    	//gets Student_info as refence and calls the next grade function
    	double grade(const Student_info& s)
    	{
    		return grade(s.midterm, s.final, s.homework);
    	}
    	
    
    	//grade()
    	//throws error if no homework grades were added
    	//passes to median
    	double grade(double midterm, double final, const std::vector<double>& hw)
    	{
    		int oops = 0;
    		hw.size() == 0 ? throw std::domain_error("Student has done no homework"):
    	    ++oops;
    
    		return grade(midterm, final, median(hw));
    	}
    
    
    	//median()
    	//calculates median for homework grades
    	double median(const std::vector<double>& v)
    	{
    		typedef std::vector<double>::size_type vec_sz;
    
    		std::vector<double> vec;
    		vec = v;
    		
    		vec_sz size = vec.size();
    		
    		size == 0 ? std::domain_error("Median of an empty vector"):
    
    		std::sort (vec.begin(), vec.end());
    
    		vec_sz mid = size/2;
    
    		return size % 2 == 0 ? (vec[mid] + vec[mid-1]) / 2 : vec[mid];
    
    	}
    
    	//grade()
    	//computes final grade
    	double grade(double midterm, double final, double homework)
    	{
    		return (0.2 * midterm) + (0.4 * final) + (0.4 * homework);
    	}
    
    
    
    #endif

  2. #2
    Registered User
    Join Date
    Jun 2003
    Posts
    4
    Hmmmm.... I spotted one problem.

    I screwed up using that short if-then-else statement in read(). Not sure what effect exactly that will have. Ill be back...

  3. #3
    Registered User
    Join Date
    Jun 2003
    Posts
    4
    Im such an idiot, sorry to have bothered you all. Once I changed that, it seems to have worked(at least printing names.)

    Even though I answered the question myself, I wouldnt mind hearing anyones input on the program.

  4. #4
    Registered User
    Join Date
    Jun 2003
    Posts
    4
    Code:
    for (int i = 0; i != students.size(); ++i)
    	{
    		//write name padded on right to maxlen + 1
    		cout << students[i].name
    		    << string(maxlen + 1 - students[i].name.size(), ' ');
    
    		//compute and write grade
    		double final_grade = grade(students[i]);
    		streamsize prec = cout.precision();
    		cout << setprecision(3) << final_grade
    			 << setprecision(prec);
    
    		cout << endl;
    	}
    there is the final for statement in main to finish out the program, i doubt anyone cares. It is my first C++ program, yay!

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