Thread: 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