Deleting nodes that are outside of a specific numeric range in a singly linked list - c++

Question

I am working on this program that reads a text file and grabs the data out of the text file and inserts it into nodes of a linked list.
I have the whole program running and working fine besides node deletion. I am filtering the data from the text file so I only need to print out the data that have values within a certain range. I can do this with an if() statement and it works fine but that's not the result I want.
I want to delete the nodes that are outside of the specified range and free up the memory that they are using. I have a few lines of code that I wrote that try to do this but it just ends up deleting the entire list. So if anyone could point me in the right direction and tell me what I'm doing wrong that would be great!
#include <fstream>
#include <iostream>
using namespace std;
struct Employee
{
string firstN;
string lastN;
float salary;
float bonus;
float deduction;
Employee *link;
};
typedef Employee* EmployPtr;
void insertAtHead( EmployPtr&, string, string, float, float,float );
void insert( EmployPtr&, string, string, float, float,float );
float netSalary( EmployPtr& );
int main()
{
//Open file
fstream in( "payroll.txt", ios::in );
//Read lines
string first, last;
float salary, bonus, deduction;
EmployPtr head = new Employee;
//Inserts all the data into a new node in the linked list, creating a new node each time the loop executes.
while( in >> first >> last >> salary >> bonus >> deduction)
insertAtHead (head, first, last, salary, bonus, deduction);
//Close file
in.close();
cout << "-Salary in the range of ($45,000 - $60,000)-\n" << "Printed in format: First Name, Last Name, Salary, Bonus, Deduction, Net Salary.\n";
EmployPtr iter, temp;
for(iter = head; iter!= NULL; iter = iter->link)
{
temp = head;
//Deletes nodes outside of range.
while(netSalary(iter)<45000 || netSalary(iter)>60000)
{
EmployPtr nodeToDelete = temp;
temp = temp->link;
delete nodeToDelete;
}
cout << iter->firstN << ", " << iter->lastN << ", " << iter->salary << ", " << iter->bonus << ", " << iter->deduction << ", " << netSalary(iter) <<endl;
}
return 0;
}
//Based off of the input values, this function will create a new node and insert it at the beginning of the linked list. This function ONLY allows insertion at the beginning of the list and no where else.
void insertAtHead(EmployPtr& head, string firstValue, string lastValue,
float salaryValue, float bonusValue,float deductionValue)
{
EmployPtr tempPtr= new Employee;
tempPtr->firstN = firstValue;
tempPtr->lastN = lastValue;
tempPtr->salary = salaryValue;
tempPtr->bonus = bonusValue;
tempPtr->deduction = deductionValue;
tempPtr->link = head;
head = tempPtr;
}
//Based off of the input values, this function creates a new node and inserts it AFTER the node provided in the argument.
void insert(EmployPtr& afterNode, string firstValue, string lastValue,
float salaryValue, float bonusValue,float deductionValue)
{
EmployPtr tempPtr= new Employee;
tempPtr->firstN = firstValue;
tempPtr->lastN = lastValue;
tempPtr->salary = salaryValue;
tempPtr->bonus = bonusValue;
tempPtr->deduction = deductionValue;
tempPtr->link = afterNode->link;
afterNode->link = tempPtr;
}
//This function calculates a net salary based off of the salary, bonus, and deduction variables of the input node.
float netSalary(EmployPtr& node)
{
float netSalary, newDeduction;
newDeduction = ((node->salary) + (node->bonus)) * (node->deduction);
netSalary = (node->salary + node->bonus) - newDeduction;
return netSalary;
}
EDIT: Changed && back to || still having issue.
EDIT #2: Solution
while(netSalary(iter)<45000 || netSalary(iter)>60000)
{
EmployPtr nodeToDelete = new Employee;
nodeToDelete = iter;
iter = iter->link;
delete nodeToDelete;
}

Answer 1

This line right here:
while(netSalary(iter)<45000 && netSalary(iter)>60000)
I believe your conditional should be OR (||). It would not make sense for a value to both be less than 45000 and more than 60000 at the same time.
Given a value 25000, it will be less than 45000, but not more than 60000, therefore nothing will ever get deleted.
Edit:
Perhaps try something along these lines:
for (iter = head; iter != NULL; iter = iter->link)
{
cout << iter->salary; // so you can see what node it's looking at
if (netSalary(iter) < 45000 || netSalary(iter) > 60000)
{
EmployPtr nodeToDelete = iter;
iter = iter->link; // difference here is that you're explicitly moving the iter forward
delete nodeToDelete;
}
}

Answer 2

I think you want the condition to be
while(netSalary(iter) >= 45000 && netSalary(iter) <= 60000)
I say think because I don't see a statement of what you actually want to filter out.

Answer 3

You should change the while condition, as a start. The '&&' should be '||' because it doesn't make sense to have '< 45000' while at the same time being greater than 60000. Also, as an alternative, why not skip adding nodes to the list entirely if they don't meet these conditions? In other words, while creating the list, check these conditions and don't add to the list if they aren't met. That way you aren't creating a list and then immediately coming back and modifying it.
EDIT:
Okay, the problem, I believe, is with the while loop using 'iter'. As soon as the iterator matches your condition in the while loop, you do nothing to move the iterator forward after that (because you don't get back out to the for loop) and therefore delete the rest of the list inside the while loop. Try changing the while to an 'if' and see what you get.

Answer 4

The most recent solution should take care of the main issue (deleting the entire list because the loop started with head instead of iter), but you may still run into another issue. If the last element is deleted, the next time the loop conditional is checked, netSalary will be called on a null pointer (as iter will be null once it's advanced to iter->link). Furthermore, attempting to modify that loop to account for the null pointer could instead lead the outside for loop attempting to access the link member of a null pointer.
The simplest solution that I could suggest would be to modify the code to use just one while loop and conditional, as shown in the following code:
EmployPtr iter = head, temp;
while(iter!= NULL)
{
if(netSalary(iter)<45000 || netSalary(iter)>60000)
{
// bad node, delete and advance
EmployPtr nodeToDelete = iter;
iter = iter->link;
delete nodeToDelete;
}
else
{
// good node, write and advance
cout << iter->firstN << ", " << iter->lastN << ", " << iter->salary << ", " << iter->bonus << ", " << iter->deduction << ", " << netSalary(iter) <<endl;
iter = iter->link;
}
}