Help with selection sort

[louis12]

Can someone explain to me how the void sortSelect(double arr[], int num, int id[], int qty[], int rop[]) works in this code? The code inputs information from a file.
This is the file.
4456 17.80 45 20
1278 13.50 20 30
6273 12.95 10 15
7821 45.20 21 20

Each row represents a number and then we are suppose to sort if from low to high based on the first column. I don;t really know how the selection sort works and how it moves the other columns to the correct places too because they are parallel array and all the numbers are in groups and the need to be in the same place after moving.

#include <iostream>
#include <fstream>
using namespace std;

#define MAX 50
//declare functions
int input(ifstream&, int[], double[], int [], int []);
void output(ofstream&, int[], double[], int[], int[], int howMany);
int search(int[], int, int);
int getExpensive(double[], int);
void sortSelect(double arr[], int num, int id[], int qty[], int rop[]);

int main(void)
{
	//Declare variables
	ifstream inFile; ofstream fpOut;
	int id[MAX];
	double price[MAX];
	int qty[MAX];
	int rop[MAX];
	int number; int target; int found; int index;

	//Open file
	inFile.open("products.txt");
	if (inFile.fail())
	{
		cout << "No such file";
		system("pause");
		exit(100);
	}
	fpOut.open("inventOut.txt");
	//Input the entire contents of the product file
	number = input(inFile, id, price, qty, rop);

	//Looking for a particular product 
	cout << "Input product id for search: ";
	cin >> target;
	
	found = search(id, number, target);
	if (found == -1)
		cout << "No Such Product!" << endl;
	else
	   cout << id[found] << "\t" << price[found] << "\t" << qty[found] << "\t" 
		<< rop[found] << endl;
	
	//Find most expensive
	index = getExpensive(price, number);
	cout << "Most expensive:" << id[index] << "\t" << price[index] << endl << endl;
	//Sort by the product id 
	sortSelect(price, number, id, qty, rop);

	//Output each product's id, quantity on hand, re-order point, and price
	output(fpOut, id, price, qty, rop, number);
	system("pause");
	return 0;
}
int input(ifstream& inFile, int id[], double price[], int qty[], int rop[])
{
	/*Pre: inFile - reference data file
	       id[] - array of product ids
		   price[] - array of unit cost
		   qty[] - array of quantity on hand
		   rop[] - array of reorder point for  each product
	 Post: Number of products
	 Purpoe: input entire inventory into parallel arrays*/

	int num = 0;

	while (!inFile.eof())
	{
		inFile >> id[num];
		inFile >> price[num] >> qty[num] >> rop[num];
		num++;
	}
	return num;
}//input
void output(ofstream& fpOut, int id[], double cost[], int qty[], int rop[], int num)
{
	fpOut << "Mary Pape" << endl << endl;
	for (int i = 0; i < num; i++)
		fpOut << id[i] << "\t" << cost[i] << "\t" << qty[i] << "\t" << rop[i] << endl;

}
int search(int id[], int num, int target)
{
	/*Pre: id[] - array of product codes
	       num - number of items in inventory
		   target - product being searched for
	  Post: the index of the target
	  Purpose: Search inventory for specific item*/

	int found = -1;

	for (int i = 0; i < num; i++)
	{
		if (target == id[i])
			found = i;
	}

	return found;
}
int getExpensive(double price[], int num)
{
	int index = 0;
	double great = price[index];

	for (int i = 0; i < num; i++)
	{
		if (price[i] > great)
		{
			index = i;
			great = price[index];
		}
	}
	return index;
}
void sortSelect(double arr[], int num, int id[], int qty[], int rop[])
{
	int current; int walker;
	int smallestIndex;
	double temp; int tempInt;

	for (current = 0; current < num - 1; current++)
	{
		smallestIndex = current;
		for (walker = current; walker < num; walker++)
		{
			if (arr[walker] < arr[smallestIndex])
				smallestIndex = walker;
		}//for walker

		//Swap to position smallest at what is the current position
		temp = arr[current];
		arr[current] = arr[smallestIndex];
		arr[smallestIndex] = temp;
		
		tempInt = id[current];
		id[current] = id[smallestIndex];
		id[smallestIndex] = tempInt;

		tempInt = qty[current];
		qty[current] = qty[smallestIndex];
		qty[smallestIndex] = tempInt;

		tempInt = rop[current];
		rop[current] = rop[smallestIndex];
		rop[smallestIndex] = tempInt;
	}//for current 
	return;
}

[louis12]

Anyone? I need to finish this project.

[Viiarge]

What do you need help with exactly?

This function seems to be putting the elements of the first argument (the double array arr) in an ascending order.

current is basically your count variable, like a 'i' in a standard For Loop.
and
num seems to be the number where you want your loops to end at :

for (current = 0; current < num - 1; current++)
	{...

temp and tempInt are buffers used to store temporary data during a data swap.

walker is also a counter, like current, but this one is used for the 2nd For Loop and as I can see, It does look like it gonna do one less iteration each time current is augmented by 1 :

for (walker = current; walker < num; walker++)
		{...

My current guess if that each of those columns in your file is suposed to become an array at somepoint in your program (double arr[], int id[], int qty[] and int rop[]). Then, this function is used to place the elements in the correct order.

If you need help, keep posting here ! Good luck and happy coding !