cannot delete from empty list

[seungyeon]

cannot delete from empty list

user inputs 1 line
user deletes 1 line
user deletes 3rd line which is nothing *crashes here*

#include <iostream>
#include <string>
#include <list>
#include <iterator>
#include <algorithm>

using namespace std;

const int NUM_LINES = 5;

template < typename ITERATOR >
ITERATOR my_next( ITERATOR iter, typename iterator_traits<ITERATOR>::difference_type n = 0 )
{
    advance( iter, n ) ;
    return iter ;
}

void inputf(list<string> &L);
void deleteone(list<string> &L);
void deleteall(list<string> &L);
void print(list<string> &L);

int main()
{
	cout << "This program will take in lines up to 5 you have inputed and you can delete, add, or print to the list." << endl;
	list <string> myList;
	list <string>::iterator it = myList.begin();
	
	
	int repeat;
	do{
		
		//input line block
		if(repeat == 1)
		{
			inputf(myList);
			if (myList.size() > 5)
 		   		{
 		   			cout << "List is full. Cannot add more to list, please delete a line." << endl;
 			   		repeat = 2;
				}
		}
		
		//delete one line
		if(repeat == 2)
		{
			deleteone(myList);
		}
		
	
		
		//print block
		if(repeat == 4)
		{
			print(myList);
		}
		
		
		
	cout << endl;
	cout << "What do you want to do:" << endl 
	<< "1. Add a line" << endl
	<< "2. Delete a line" << endl
	
	<< "4. Print all the lines" << endl
	
	<< "Please enter a number above: ";
	cin >> repeat;
	}while(repeat >= 1 && repeat <= 5);
	
	return 0;
}

//input function
void inputf(list<string> &L)
{
	char input[40];
	int lines;
	cout << "How many lines do you want to enter: ";
	cin >> lines;
	if(lines <= 0)
	{
		cout << "WHAT?! You have to input something. Enter again: ";
		cin >> lines;
	}
	cout << "Enter lines";
	cout << endl;
	for(int ins = 0; ins <= lines; ins++)
	{
		cin.getline(input,40);
	  	L.push_back(input);
	}

}

//print function
void print(list<string> &L)
{
	cout << endl; 
    if(L.empty())
    {
    	cout << "This list is empty." << endl;
	}
    
	list<string>::iterator inx = L.begin();      //inx = 5; // Can only assign iterator values 
	
	for (inx = L.begin(); inx != L.end(); ++inx)
    cout << *inx << '\n';
}

//delete function
void deleteone(list<string> &L)
{
	list<string>::iterator inx = L.begin();
	if (L.size() < 1)
 		   	{
 		   		cout << "List is empty. Cannot delete lines from list." << endl;
				L.clear();
			}
			else
			{
			int choose;
			cout << "Which line to delete? (Line 1 is 1, Line 5 is 5): ";
			cin >> choose;
			if (choose < 1 || choose > 5)
			{
				cout << "Invalid input, enter a number between 1 and 5: ";
				cin >> choose;
			}
			advance(inx,choose);
			L.erase(inx);
		}
}

[coder777]

cannot delete from empty list

This is correct. using advance(...) The index must always be less than L.size().

Note that you are addressing the second element of the list when choose = 1.

Thus, before you access a list element via index, you need to check whether the index is within the bounds of the list not an arbitrary bound like 5. It is a list not an array.