C++ - Linked List Insertion Sort (String elements) - c++

Question

I've a homework task, where I've to sort linked list elements (strings) after first character in a string.
Example:
From: Pineapple->Apple->Ash->Abc->Pearl->Bonfire->Ball
To: Apple->Ash->Abc->Bonfire->Ball->Pineapple->Pearl (Only first char)
I made a function:
void insertionSort ()
{
first = current;
Node* insertionPointer = first;
current = current -> next;
for (start(); !end(); next()){ // Running through all list nodes
while (current != NULL) {
insertionPointer = first;
while(insertionPointer->next != current) {
if (insertionPointer->data.at(0) > current-> data.at(0)){ // Trying to sort strings alphabetically
// (after only first char)
string temp = current->data;
current->data = insertionPointer->data;
insertionPointer->data = temp;
}
else {
insertionPointer = insertionPointer->next;
}
}
}
}
}
But I get a segmentation fault - I guess that means I'm trying to get some information, that I can not access? Also, I'm not sure if:
if (insertionPointer->data.at(0) > current-> data.at(0))
Will compare strings first char? I'm just trying to experiment here. :(
Just to make sure, I'll post below also my whole code, so you can see how I structured lists and other functions. I'm new to this stuff - any information will be helpful.
Full program code:
#include <iostream>
#include <fstream>
#include <string>
#include <string.h>
using namespace std;
class Node
{
public:
string data;
Node *next;
Node (string city) { data = city; next = NULL; };
};
class List
{
protected:
Node *first, *last;
public:
Node *current;
public:
List () { first = last = current = NULL; };
void add_element (string city);
void delete_element ();
~List();
bool is_empty () { return (first == NULL); };
void start () { current = first; };
bool end () { return (current == NULL); };
void next(){if (!end())current = current -> next;};
void print();
void insertionSort ()
{
first = current;
Node* insertionPointer = first;
current = current -> next;
for (start(); !end(); next()){ // Running through all list nodes
while (current != NULL) {
insertionPointer = first;
while(insertionPointer->next != current) {
if (insertionPointer->data.at(0) > current->data.at(0)){ // Trying to sort strings alphabetically
// (after only first char)
string temp = current->data;
current->data = insertionPointer->data;
insertionPointer->data = temp;
}else{
insertionPointer = insertionPointer->next;
}
}
}
}
}
};
int main()
{
string s;
List l;
l.add_element("Pineapple");
l.add_element("Apple");
l.add_element("Ash");
l.add_element("Abc");
l.add_element("Pearl");
l.add_element("Bonfire");
l.add_element("Ball");
l.print();
cout << endl;
l.insertionSort();
l.print();
return 0;
}
void List::add_element (string city)
{
Node *p = new Node (city);
if (first == NULL) first = last = p;
else last = last -> next = p;
current = p;
};
void List::delete_element ()
{
Node *p = first;
if(!is_empty())
{ if (current == first) current = first-> next;
first = first -> next;
delete p;
if(is_empty())last = NULL;
}
};
void List::print()
{
for (start(); !end(); next())
{
cout << current->data << endl;
}
cout << endl;
};
List::~List()
{
while (!is_empty())
{
delete_element();
};
cout << "All memory of nodes deleted!"<< endl;
};

Answer 1

Your program is most likely crashing here:
while(insertionPointer->next != current) {
because insertionPointer has become null when you executed
insertionPointer = insertionPointer->next;
change the loop condition to
while(insertionPointer && insertionPointer->next != current) {