Member Avatar for theashman88

Hey I just got this book Accelerated c++ and it seems pretty good, but I'm having one problem in chapter 4. When I compile my grading program in chapter 4. I can't get the final version to work. I believe I'm supposed to enter a students name followed by grades, but I don't know how to create a condition that makes the first while loop stop, so I can show I'm done entering names and grades. I included the files that I'm working with. If you have the book they're the exact same.

#include <stdexcept>
#include <vector>
#include "grade.h"
#include "median.h"
#include "Student_info.h"

using std::domain_error;
using std::vector;

double grade(double midterm, double final, double homework)
{
       return 0.2 * midterm + 0.4 * final + 0.4 * homework;
}

double grade(double midterm, double final, const vector<double>& hw)
{
       if (hw.size() == 0)
           throw domain_error("student has done no homework");
       return grade(midterm, final, median(hw));
}

double grade(const Student_info& s)
{
       return grade(s.midterm, s.final, s.homework);
}
#ifndef GUARD_grade_h
#define GUARD_grade_h

// grade.h
#include <vector>
#include "Student_info.h"

double grade(double, double, double);
double grade(double, double, const std::vector<double>&);
double grade(const Student_info&);

#endif
#include <algorithm>
#include <iomanip>
#include <ios>
#include <iostream>
#include <stdexcept>
#include <string>
#include <vector>
#include "grade.h"
#include "Student_info.h"

using std::cin;
using std::cout;
using std::domain_error;
using std::endl;
using std::max;
using std::setprecision;
using std::sort;
using std::streamsize;
using std::string;
using std::vector;

int main()
{
	vector<Student_info> students;
    Student_info record;
    string::size_type maxlen = 0;  // the length of the longest name
    
    // read and store all the students' data
    // Invariant:  students contains all the student records read so far
    //             maxlen contains the length of the longest name in students
    while (read(cin, record)) {
        // find length of longest name
        maxlen = max(maxlen, record.name.size());
        students.push_back(record);
    }
    
    // alphabetize the student records
    sort(students.begin(), students.end(), compare);
    
    // write the names and grades
    for (vector<Student_info>::size_type i = 0;
         i != students.size(); ++i) {
         
         // write the name, padded on the right to maxlen +1 characters
         cout << students[i].name
              << string(maxlen + 1 - students[i].name.size(), ' ');
         
         // compute and write the grade
         try {
             double final_grade = grade(students[i]);
             streamsize prec = cout.precision();
             cout << setprecision(3) << final_grade
                  << setprecision(prec);
         } catch (domain_error e) {
             cout << e.what();
         }
         cout << endl;
    }
    return 0;
}
// source file for the median function
#include <algorithm>    // to get the decleration of sort
#include <stdexcept>    // to get the decleration of domain_error
#include <vector>       // to get the decleration of vector

using std::domain_error;
using std::sort;
using std::vector;

// compute the median of a vector<double>
double median(vector<double> vec)
{
       typedef vector<double>::size_type vec_sz;
       
       vec_sz size = vec.size();
       if (size == 0)
           throw domain_error("median of an empty vector");
       
       sort(vec.begin(), vec.end());
       
       vec_sz mid = size/2;
       
       return size % 2 == 0 ? (vec[mid] + vec[mid-1]) /2 : vec[mid];
}
#ifndef GUARD_median_h
#define GUARD_median_h

// median.h
#include <vector>
double median(std::vector<double>);

#endif
// source file for Student_info-related functions
#include "Student_info.h"

using std::istream;
using std::vector;

bool compare(const Student_info& x, const Student_info& y)
{
     return x.name < y.name;
}

istream& read(istream& is, Student_info& s)
{
         // read and store the student's name and midterm and final exam grades
         is >> s.name >> s.midterm >> s.final;
         
         read_hw(is, s.homework);  // read and store all the student's homework grades
         return is;
}
istream& read_hw(istream& in, vector<double>& hw)
{
         if (in) {
                 // get rid of previous content
                 hw.clear();
                 
                 // read homework grades
                 double x;
                 while (in >> x)
                     hw.push_back(x);
                 
                 // clear the stream so that input will work for the next student
                 in.clear();
         }
         return in;
}
#ifndef GUARD_Student_info
#define GUARD_Student_info

// Student_info.h header file
#include <iostream>
#include <string>
#include <vector>

struct Student_info {
       std::string name;
       double midterm, final;
       std::vector<double> homework;
};

bool compare(const Student_info&, const Student_info&);
std::istream& read(std::istream&, Student_info&);
std::istream& read_hw(std::istream&, std::vector<double>&);
#endif
  • 5 Contributors
  • 8 Replies
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  • 9 Hours Discussion Span
  • Latest Post Latest Post by mvmalderen

Recommended Answers

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Member Avatar for Tom Gunn

That's a lot of stuff to look at. Can you boil it down to something small enough to post in code tags?

Member Avatar for theashman88 
int main()
{
    vector<Student_info> students;
    Student_info record;
    string::size_type maxlen = 0;  // the length of the longest name
    
    // read and store all the students' data
    // Invariant:  students contains all the student records read so far
    //             maxlen contains the length of the longest name in students
    while (read(cin, record)) {
        // find length of longest name
        maxlen = max(maxlen, record.name.size());
        students.push_back(record);
    }
    
    // alphabetize the student records
    sort(students.begin(), students.end(), compare);
    
    // write the names and grades
    for (vector<Student_info>::size_type i = 0;
         i != students.size(); ++i) {
         
         // write the name, padded on the right to maxlen +1 characters
         cout << students[i].name
              << string(maxlen + 1 - students[i].name.size(), ' ');
         
         // compute and write the grade
         try {
             double final_grade = grade(students[i]);
             streamsize prec = cout.precision();
             cout << setprecision(3) << final_grade
                  << setprecision(prec);
         } catch (domain_error e) {
             cout << e.what();
         }
         cout << endl;

Here are the functions for the read(cin, record)

istream& read(istream& is, Student_info& s)
{
         // read and store the student's name and midterm and final exam grades
         is >> s.name >> s.midterm >> s.final;
         
         read_hw(is, s.homework);  // read and store all the student's homework grades
         return is;
}
istream& read_hw(istream& in, vector<double>& hw)
{
         if (in) {
                 // get rid of previous content
                 hw.clear();
                 
                 // read homework grades
                 double x;
                 while (in >> x)
                     hw.push_back(x);
                 
                 // clear the stream so that input will work for the next student
                 in.clear();
         }
         return in;
}

If you need anything else please let me know.

Member Avatar for Tom Gunn

The read() function returns the stream, so you should be able to signal EOF to stop the first loop. On Linux it's a Ctrl+D key combination and on Windows it's Ctrl+Z.

commented: Quick help +1
Member Avatar for Dave Sinkula

Or pipe the input from a file.

Member Avatar for Lerner

How about using a sentinnel/flag? A little bit of a hassle to enter an additional keystroke, but it is completely portable, offers complete control without using magical combinations, etc.

bool moreInput = true;
char temp;
while(moreInput)
{
   //get input
   cout << "enter y to keep going, anything else to stop" << '\n';
   cin >> temp;
   if(temp == 'y')
     moreInput = false;
}
Member Avatar for theashman88

Alright when I push ctrl+z it displays this ^Z. Then I hit enter a few times and decided to just type in done or something random. Then it displayed the names and grades. Any ideas?

Member Avatar for theashman88

oh nvm I see I had too end two loops. Alright whew that works out. Thank you all for all your help.

Member Avatar for mvmalderen 
bool moreInput = true;
char temp;
while(moreInput)
{
   //get input
   cout << "enter y to keep going, anything else to stop" << '\n';
   cin >> temp;
   if(temp == 'y')
     moreInput = false;
}

I always would write the following line: if(temp == 'y') as if( [B]tolower(temp)[/B] == 'y') because it also allows the user to enter an uppercase 'Y' :)

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