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Binary Search

Posted on 2004-04-30
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Last Modified: 2013-11-15
I am trying to do a binary search for the following program.  This program reads a txt file and sorts and outputs the student information by either grade, email, last name, or first name.  
Using binary search my program is supposed to ask the user to enter a student grade, once the user enters the grade the program outputs the closes student name with grade.  For example, if user enters 86 for the grade the program should output Alice Keith has grade of 84.6.  

The infile has this information:
Richard,Jones,richars@jones.com,78.5
Alice,Keith,alicek@yahoo.com,84.6
Diego,Salazar,ds@hotmail.com,91.2
Max,Karlov,max@kkk.org,63.2

Here is my program.
#include <iostream>
#include <fstream>
#include <string>

using namespace std;

struct Student {
    string fname;
    string lname;
    string email;
    double grade;
};

Student* list[20];

int main1()
{
   
   
    fstream inFile("studentlist.txt");
    ofstream outFile;  //output file stream variable
      outFile.open("output10p1.txt"); //open outfile
   
      //declare variables
      char str[128];
    int i=0, c;            
   
    while (!inFile.eof())
    {
        inFile.getline(str, 128);
        string line = str;
        int pos1 = line.find(",");
        string fname = line.substr(0,pos1);
        int pos2 = line.find(",",pos1+1);
        string lname = line.substr(pos1+1,pos2-pos1-1);
        int pos3 = line.find(",",pos2+1);
        string email = line.substr(pos2+1,pos3-pos2-1);
        string grade = line.substr(pos3+1,line.length()-pos3-1);
        double grd = atof(grade.c_str());
         
        list[i] = new Student;
        list[i] ->fname = fname;
        list[i] ->lname = lname;
        list[i] ->email = email;
        list[i] ->grade = grd;
        i++;
   
    }
    // SAVE THE CURRENT VALUE OF THE LOOP COUNTER. IT'S THE STUDENTS COUNT
    int count = i;
                           
    // loop will keep function until user enters "0"
    while (true)
    {
        //(0 to quit)
        cout<<"Which column would you like to sort by (0 to quit) ==> "<<endl;
            cout<<"1) First Name"<<endl<<"2) Last Name"<<endl<<"3) Email"<<endl<<"4) Grade"<<endl;
        cin>>c;  
         
        // if "0" is entered loop will terminate
        if (c == 0)
            break;

        // Loop Runs Til Count == Number Of Students Read
        for (i=0; i < count; i++)
        {
            for (int j=i+1; j < count; j++)
            {
               
                switch (c)
                {
                case 1: if (list[i]->fname > list[j]->fname){
                    Student* tmp = list[i];
                    list[i] = list[j];
                    list[j] = tmp;
                    break;
                        }
                case 2: if (list[i]->lname > list[j]->lname){
                    Student* tmp = list[i];
                    list[i] = list[j];
                    list[j] = tmp;
                    break;
                        }
                case 3: if (list[i]->email > list[j]->email){
                    Student* tmp = list[i];
                    list[i] = list[j];
                    list[j] = tmp;
                    break;
                        }
                case 4: if (list[i]->grade > list[j]->grade){
                    Student* tmp = list[i];
                    list[i] = list[j];
                    list[j] = tmp;
                    break;
                        }
                   
                }
               
            }
           
        }
            cout <<"+-----------+-------------+---------------------+--------------------+"<<endl;
        cout <<"|First Name |  Last Name  |      Email          |      Grade         |"<<endl;
            cout <<"+-----------+-------------+---------------------+--------------------+"<<endl;
            
            // statement to output sorted table
        for (i=0; i< count; i++)
        {
                  cout <<list[i]->fname<<"\t    |   "<<list[i]->lname<<"\t  |  "<<list[i]->email<<"\t|\t"<<
                         list[i]->grade <<"\t     |"<< endl;
        }
            cout <<"+-----------+-------------+---------------------+--------------------+"<<endl;
      

      }
    return 0;
}
 
0
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Question by:Steve3164
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3 Comments
 

Expert Comment

by:alexanderthegreat
ID: 10967062
would it not be better just to let the program only search for names.

0
 
LVL 9

Expert Comment

by:keteracel
ID: 10968592
looks very homeworky to me!

A binary search requires a binary tree so instead of the "Student* list[20];" (which is syntactically incorrect anyway!) you'll need to have a tree struct (or use the standard library) and a pointer to the head node. Then you'll need functions to add students and search for students.

Since it looks like you're using C++ you should make a binary tree class to do all this.

That's as much as I'm going to give you as it does look like homework to me...
0
 
LVL 39

Accepted Solution

by:
itsmeandnobodyelse earned 250 total points
ID: 10973409
I did it for you, but you should have tried to do it yourself. So i made no comments to the (tested) solution and i'll give you two tasks:

1. Student* list[20];     That will crash if the file contains more than 20 students.
    Try to use a variables

       Students** list = new Students*[20];
       int  listSize = 20;

    where you allocate new memory if  count exceeds listSize and where the contents of the previous list got copied to the new list.

2. Add comments to the prog

Regards, Alex


#include <iostream>
#include <fstream>
#include <string>
#include <algorithm>

#ifdef WIN32
#define max _cpp_max
#endif

using namespace std;

struct Student {
    string fname;
    string lname;
    string email;
    double grade;
};

Student* list[20];

void swap(Student*& ps1, Student*& ps2)
{
    Student* ps = ps1;
    ps1 = ps2;
    ps2 = ps;
}


bool isless (Student* ps1, Student* ps2, int column)
{  
    if (column == 4)
        return ps1->grade < ps2->grade;
    else if (column == 3)
        return ps1->email < ps2->email;
    else if (column == 2)
        return ps1->lname < ps2->lname;
    else /* if (column == 1) */
        return ps1->fname < ps2->fname;
}

void sort(Student** list, int count, int column)
{
    for (int i = 0; i < count; i++ )
    {
        for (int j = i +  1; j < count; j++ )
        {
            if ( isless( list[j], list[i], column ) )
                swap( list[i], list[j] );
        }
    }
}

int main ()
{
    fstream inFile("studentlist.txt");
   
    char   str[128];
    int    i=0, c, a;
    double g;
   
    while (!inFile.eof())
    {
        inFile.getline(str, 128);
        string line = str;
        cout << line <<endl;
        int pos1 = line.find(",");
        string fname = line.substr(0,pos1);
        int pos2 = line.find(",",pos1+1);
        string lname = line.substr(pos1+1,pos2-pos1-1);
        int pos3 = line.find(",",pos2+1);
        string email = line.substr(pos2+1,pos3-pos2-1);
        string grade = line.substr(pos3+1,line.length()-pos3-1);
        double grd = atof(grade.c_str());
        list[i] = new Student;
        list[i] ->fname = fname;
        list[i] ->lname = lname;
        list[i] ->email = email;
        list[i] ->grade = grd;
        i++;
   
    }
    int count = i;

    while (true)
    {
        cout << "What do you want to do next?" << endl << endl;
        cout << "1\tSort list\n2\tSearch list for closest grade" << endl << endl;
        cout<<"Enter action code (0 to quit) ==>";
        cin >> a;
        if (a == 0 || a > 2)
            break;
        switch (a)
        {
        case 1:
            while (true)
            {
                cout<<"Which column would you like to sort by (0 to quit) ==>";
                cin >> c;
                if (c == 0 || c > 4)
                    break;
               
                sort (list, count, c);
               
                for (i=0; i < count; i++)
                {
                    cout <<list[i]->fname<<"\t    |   "<<list[i]->lname<<"\t  |  "<<list[i]->email<<"\t|\t"<<
                        list[i]->grade <<"\t     |"<< endl;
                }
            }
            break;

        case 2:
            while (true)
            {
                cout<<"What is the grade you are searching for (0 to quit) ==>";
                cin >> g;
                if (g == 0.0)
                    break;

                // First, we sort by column 4
                sort(list, count, 4);

                int n  = 0;
                int nl = 0;
                int nu = count;

                while (nl < nu)
                {
                    n = (nl + nu) / 2;    // get the middle
                    if (list[n]->grade == g)
                    {
                        nl = n;
                        break;
                    }
                    else if (list[n]->grade < g)
                        nl = n + 1;
                    else
                        nu = n;
                }
                // now nl is the position where the given grade would be inserted to maintain sort order
                // check neighbors to get closest
                n = nl;
                if (nl > 0)
                {
                    if (nl == count)
                        n = nl - 1;
                    else if ((g - list[nl-1]->grade) < (list[nl]->grade - g))
                        n = nl - 1;
                    else
                        n = nl;
                }
                cout <<list[n]->fname<<"\t    |   "<<list[n]->lname<<"\t  |  "<<list[n]->email<<"\t|\t"<<
                    list[n]->grade <<"\t     |"<< endl;
                cout << "is closest to the given grade " << g << endl << endl;
            }
            break;
        }    
       
    }
    return 0;
}


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