Question

The screenshot below states "The singly linked list STL container std::forward_list has an erase function, which can be directly used here. But that function erases AFTER the item pointed to, not the one pointed to like the other containers. A singly linked list cannot look backwards, only forward. You need to convert the zero-based offset from the top to an iterator by advancing _groceries_sl_list.before_begin() offsetFromTop times. The STL has a function called std::next() that does that, or you can write your own loop." How do I code this? If this isn't specific enough please try to use some kind of generalized code. Also this is C++.

A t W [Groceryltem.hpp - -/Desk... [Assignment - Mozilla Firefox] - [to do4.png - Image Viewer ... GroceryList.cpp - Sequence ... GroceryList.cpp - Sequence Containers Homework - Visual Studio Code File Edit Selection View Go Debug Terminal Help O -) 01 Mar, 23:44 - + X ... o C Groceryltem.cpp * GroceryList.cpp > 355 I 356 357 C GroceryList.cpp X Groceryltem.hpp GroceryList:remove(const Groceryltem &) II/ END-TO-DO I a DEEZER 9 358 359 360 **** Remove from singly linked list *** 361 362 I ☆ 363 364 365 IIIIIIIIIIIII TO-DO I/IIIIIIIIIIIIIIIIIII /// The singly linked list STL container std:: forward_list has an erase function, which can be directly used here. But that /// function erases AFTER the item pointed to, not the one pointed to like the other containers. A singly linked list cannot /// look backwards, only forward. You need to convert the zero-based offset from the top to an iterator by advancing Il groceries_sl_list.before_begin() offsetFromTop times. The STL has a function called std:: next() that does that, or you /// can write your own loop. 367 368 369 MITTITITITI END-TO-DO LIITT TELE 370 371 372 // Verify the internal grocery list state is still consistent amongst the four containers if( !containersAreConsistant()) throw GroceryList :: InvalidInternalstate Ex( "Container consistency error" exception location); 373 374 } 375 376 377 void GroceryList::moveToTop( const GroceryItem & item ), 378 379 380 381 IIIIIIIIIIIIIIIIIIIIIIIII TO-DO LIITT // If the item exists, then remove and reinsert it. Else do nothing. Use Grocerylist::find() to determine if the grocery item /// exists in this grocery list 382

Answer 1

Hi,

void remove_item(forward_list<int> &ll):

1.Asks user to enter the number to be deleted

2. Searches item in forward_list, "iterator it" will store the pointer

3. If "it" points to ends of the list, then no element in forward list.

4. Else using iterator we go through the forward_list and search for "it" pointer using next(start,1).

5.Delete that start when we found the pointer "it".

next(start,1): This function returns the Iterator after advancing the positions mentioned in its arguments...

here it advance one location from where start pointed i.e., next element of start...

C++ code:

//program starts here..

#include <iostream>
#include<forward_list>
#include<algorithm>
using namespace std;

void remove_item(forward_list<int> &ll)
{
cout << "Enter number to be delted:" << endl;
int item;
cin >> item;
forward_list<int> :: iterator it;
forward_list<int> :: iterator start;
it = find(ll.begin(),ll.end(),item);//item to be deleted pointed by it
if(it == ll.end())
{
cout << "item not found" << endl;
return;
}
//From here actual code start... All deletions all pointer based
if(it == ll.begin())//if the front element to be removed
{
ll.pop_front();//using inBuilt function
}
else//Here searching for pointer not the value
{
for(start = ll.begin() ; start != ll.end() ; start++)
{
if(it == next(start,1))//if next element need to be deleted
{
ll.erase_after(start);//after start is the element to be deleted.
break;
}
}
}
}

int main() {
forward_list<int> ll = {10, 20, 30, 40, 50};
remove_item(ll);
forward_list<int> :: iterator start;
for(start = ll.begin();start != ll.end() ; start++)
cout << *start << " ";
cout << endl;
}

//Program ends here..

main.cpp saved 1 #include <iostream> 2 #include<vector> #include<algorithm> using namespace std; int find_item(vector<string>g, string item) 00 vector<string> :: iterator it; it = find(g.begin() , g.end() , item); //Iterator used to store the position of searched element if(it == g.end()// if item not found, retruns size of the vector return g.size(); return it-g.begin();//g.begin() it start position of array, iterator it index of searched it..this will give the zero indexed position... 15 } 17 18 int main() 1 int n; cout << "enter number of items:"; cin >> n; vector<string>grocery; cout << "Enter item names:" << endl; for(int i = 0; i<n; i++) string s; cin >> S; grocery.push_back(s); cout << "enter item to be searched:"; string item; cin >> item; int index = find_item(grocery , item); if (index == n) cout << "Item not found" << endl; else cout << "item found at " << index << endl; 37

./main enter number of items:5 Enter item names: apple coconut banana grapes oranges enter item to be searched : banana item found at 2 ./main enter number of items:5 Enter item names: apple coconut banana grapes oranges enter item to be searched : abc Item not found