Question

I have created a hash class for an assignment in school that implements hashing and takes care of collisions. When testing this class by uploading 25 items (student records), I noticed that my hash class is simply inserting each item into the array used for storage in order(rather then using the hash code). In debug mode however the insertItemCollision() function calculates position correctly but the item is inserted in sequential order none the less.

What is causing this to happen and how can it be fixed? Thanks!

hash.h

//hash.h
#include <string>
struct Student
{
    std::string name;
    std::string id;
};

class MyHash{
public:
    MyHash();
    int hashCode(int, int);
    void insertItemCollision(std::string, std::string);
    std::string retrieveItem(std::string);
    Student students[100];
};

hash.cpp

//hash.cpp
#include <iostream>
#include "Hash.h"


MyHash::MyHash()
{
}

int MyHash::hashCode(int id, int max)
{

  return (id % max);
}

void MyHash::insertItemCollision(std::string id, std::string name)
{
    int idInt = atoi(id.c_str());
    int location;


  location = hashCode(idInt, 100);
  while (students[location].id != "")
    location = (location + 1) % 100;
  students[location].id = id;
  students[location].name = name;
}


std::string MyHash::retrieveItem(std::string id)
{
  int location;
  int startLoc;
  int idInt = atoi(id.c_str());
  bool moreToSearch = true;
  bool found;
  std::string item;

  startLoc = hashCode(idInt, 100);
  location = startLoc;
  do
  {
      if (students[location].id == id || students[location].id == "")
      moreToSearch = false;
    else
      location = (location + 1) % 100;
  } while (location != startLoc && moreToSearch);
  found = (students[location].id == id);
  if (found)
      item = students[location].name;
  return item;
}

students.txt

//students.txt
9892 Zack Lewis
4592 Ken Rodriguez
9819 Anderson Clark
1519 Ben Robinson
4597 Abigail Martinez
8542 Madison Garcia
6113 Mia Thompson
8591 Chloe Martin
9491 Daniel Harris
1698 Aiden White
5984 Alexander Walker
6541 Ethan Jackson
9549 Michael Thomas
5949 Emily Anderson
9861 Ava Taylor
5412 Noah Moore
6262 Olivia Wilson
1954 Jayden Miller
4954 William Davis
9567 Emma Brown
5195 Mason Jones
9195 Isabella Williams
5199 Sophia Johnson
1294 Jacob Smith

driver.cpp

//driver.cpp
#include <iostream>
#include<string>
#include<fstream>
#include "Hash.h"
using namespace std;


int read(string[]);
void splitString(string, Student&);
void init(string[], MyHash*, int);
int showMenu();

int main()
{
    int size;
    int choice;
    string input[100];
    MyHash* h = new MyHash();
    size = read(input); 
    init(input, h, size);

    do
    {
        choice = showMenu();
        if (choice == 1)
        {
            string id;
            cout << "Enter the id of the sutdent you would like to find: " << endl;
            cin >> id;
            std::string s = (*h).retrieveItem(id);
            if (s != "")
                cout << "The students name is: "<< s << endl;
            else
                cout << "No students matching that id was found!" <<endl;
        }

    }while (choice != 2);

    system("pause");
    return 0;
}

int read(string st[])
{
    int size = 0;
    ifstream infilestream;
    infilestream.open("test.txt");


    for(int i = 0; infilestream.good(); i++)
    {
        getline(infilestream, st[i]);
        cout<<st[i] <<endl;
        size++;
    }
    infilestream.close();
    return size;
}

void splitString(string record, Student& s)
{
    s.id = record.substr(0, 4);
    s.name = record.substr(5, record.length());
}

void init(string inputs[], MyHash* myHash, int size)
{
    for(int i = 0;i < size; i++)
    {
        splitString(inputs[i],myHash->students[i]);
        //cout << stus[i].name << " " << stus[i].id << endl;
        myHash->insertItemCollision(myHash->students[i].id, myHash->students[i].name);
    }
}

int showMenu()
{
    int chs;
    cout << "1. Find student by id." << endl;
    cout << "2. Exit." << endl;
    cin >> chs;
    return chs;
}

Fix:
These two functions were updated:

Student* splitString(string record)
{
    Student* stu = new Student();
    stu->id = record.substr(0, 4);
    stu->name = record.substr(5, record.length());
    return stu;
}

void init(string inputs[], MyHash* myHash, int size)
{
    for(int i = 0;i < size; i++)
    {
        Student* s = new Student();
        s = splitString(inputs[i]);//,myHash->students[i]);
        //cout << stus[i].name << " " << stus[i].id << endl;
        //myHash->insertItemCollision(myHash->students[i].id, myHash->students[i].name);
        myHash->insertItemCollision(s->id, s->name);
    }
}

Answer 1

The problem is that you are using the member students when you insert (insertItemCollision) but also when you split (splitString). So they get overwritten.