How does selection sort work? - c++

Question

This is a selection sort that I'm trying and I don't understand why it isn't working. My understanding is that selection sort scans a vector for the smallest value which when it finds it moves it to the beginning of the vector. It preforms another scan this time ignoring the first element and doing it all over again until n - 1 times where n is the length of the vector.
#include <iostream>
#include <string>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <cstdlib>
#include <map>
using namespace std;
int main()
{
vector <string> vName, vID, vClass;
string sName, minValue, sID, sClass, sSearch, sQuestion, ssSearch, sSearchN, sSearchI;
int iSize, iStudent;
// Display initial vector size
iSize = vName.size();
cout << "Student list starts with the size:" << iSize << endl;
// Get size of list from user
cout << "How many students would you like to add?" << endl;
cin >> iStudent;
cin.ignore();
// Get names, ids, and classes
for (int i = 0; i < iStudent; i++)
{
cout << "Student" << i + 1 << ":\n";
cout << "Please enter the student name: ";
getline(cin, sName);
vName.push_back(sName);
cout << "Enter ID number ";
getline(cin, sID);
vID.push_back(sID);
cout << "Enter class name ";
getline(cin, sClass);
vClass.push_back(sClass);
}
// Display header
cout << "The list of students has the size of: " << iStudent << endl;
cout << "The Student List" << endl;
cout << "\n";
cout << "Name:" << setw(30) << "ID:" << setw(38) << "Enrolled Class : " << endl;
cout << "--------------------------------------------------------------------------";
cout << "\n";
// for loop for displying list
for (int x = 0; x < vName.size() && vID.size() && vClass.size(); x++)
{
cout << vName[x] << "\t \t \t" << vID[x] << "\t \t \t" << vClass[x] << endl;
}
// Sorting function and for loop to display sorted names
cout << "\n";
cout << "The Student List after Sorting:" << endl;
cout << "\n";
//*************************************
int startScan, minIndex;
for (startScan = 0; startScan < vName.size() - 1; startScan++)
{
minIndex = startScan;
minValue = vName[startScan];
for (int index = startScan + 1; index < vName.size(); index++)
{
if (vName[index] < minValue)
{
minValue = vName[index];
minIndex = index;
}
}
vName[minIndex] = vName[startScan];
vName[startScan] = minValue;
vID[minIndex] = vID[startScan];
vID[startScan] = minValue;
vClass[minIndex] = vClass[startScan];
vClass[startScan] = minValue;
}
//******************
//sort(vName.begin(), vName.end());
//for (int y = 0; y < vName.size(); y++)
//{
// cout << vName[y] << endl;
//}
cout << "\n";
// Search function uses a do while loop that loops so long as the user inputs a "y" or "Y"
do
{
int iPick;
cout << "Search Menu:" << endl;
cout << "1. By Name\n";
cout << "2. By ID\n \n";
cin >> iPick;
if (iPick == 1)
{
cout << "Please Enter a name to be searched:" << endl;
getline(cin >> ws, sSearchN);
if (binary_search(vName.begin(), vName.end(), sSearchN))
{
cout << sSearchN << " was found." << endl << endl;
}
else
{
cout << sSearchN << " was not found." << endl << endl;
}
cout << "Would you like to search another name?" << endl << endl;
cout << vName[0];
cout << "Please enter Y for Yes and N for No:" << endl << endl;
getline(cin >> ws, sQuestion);
}
else
{
cout << "Please Enter an ID to be searched:" << endl;
getline(cin >> ws, sSearchI);
if (binary_search(vID.begin(), vID.end(), sSearchI))
{
cout << sSearchI << " " << "was found" << endl << endl;
cout << "Please enter Y for Yes and N for No:" << endl << endl;
getline(cin >> ws, sQuestion);
}
else
{
cout << sSearchI << " " << "was not found." << endl << endl;
cout << "Please enter Y for Yes and N for No:" << endl << endl;
getline(cin >> ws, sQuestion);
}
}
} while (sQuestion == "Y" || sQuestion == "y");
cout << "Thank you for using this program!" << endl;
return 0;
}
EDIT: posted whole program
So the issue is it doesn't sort at all, just gives back vName unsorted.

Answer 1

Okay upon more further study of the code I think I've figured it out.
So looking at the part of the code that is sorting, the way that it works is actually pretty simple. startScan is an int increments until it becomes equal to the size of the vector in the for loop. In this case it is vName. minIndex will hold the smallest index number which at the time of initialization will be equal to the starScan. Finally minValue is a string (in this case because we have a vector of strings) that acts as a temporary container for the element at vName[scanStart]. In the second for loop index will be incremented through the vector and will test if the element vName[index] is smaller than the temproray container i talked about earlier. If it is than the new temp will be vName[index] after that is done it will exit the inner loop and update and move on to the next smallest value in vName. Understanding this it's easy to make it so that the sorting happens with 2 other vectors. All one has to do is create containers for those vectors like the ones i have here minValueA and minValueB. They will simply be changing as vName changes. That way everything stays in the order in which vName is ordered. I hope that helps someone!
int startScan, minIndex;
string minValue, minValueA, minValueB;
for (startScan = 0; startScan < vName.size() - 1; startScan++)
{
minIndex = startScan;
minValue = vName[startScan];
minValueA = vID[startScan];
minValueB = vClass[startScan];
for (int index = startScan + 1; index < vName.size(); index++)
{
if (vName[index] < minValue)
{
minValue = vName[index];
minValueA = vID[index];
minValueB = vClass[index];
minIndex = index;
}
}
vName[minIndex] = vName[startScan];
vName[startScan] = minValue; //values for vName are being added to the other ones.
vID[minIndex] = vID[startScan];
vID[startScan] = minValueA;
vClass[minIndex] = vClass[startScan];
vClass[startScan] = minValueB;
}
//******************
sort(vName.begin(), vName.end());
for (int y = 0; y < vName.size(); y++)
{
cout << vName[y] << "\t \t \t " << vID[y] << "\t \t \t " << vClass[y] << endl;
}