In this method, all nodes in the linked list with specified key (value) is deleted. For example - if the given List is 10->20->30->10->20 and all occurrences of 20 are deleted, the Linked List becomes 10->30->10.

If the head of the linked list is not null and the value stored at head is equal to key, then adjust the head as head next and delete previous head. Keep on doing the same process until the new head becomes null or not equal to the key. After that create a temp node to traverse through the list and delete those nodes with value equal to the key and adjust links accordingly.

The function pop_all is created for this purpose. It is a 2-step process.

```void pop_all(int key) {
Node* nodeToDelete;

//1. if the head is not null and value stored at
//   head is equal to key, keep on adjusting the
//   head as head next and deleting previous head
//   until new head becomes null or not equal to key
while(head != NULL && head->data == key) {
nodeToDelete = head;
head = head->next;
free(nodeToDelete);
}

//2. create a temp node to traverse through the
//   list and delete nodes with value equal to
//   key and adjust links accordingly
Node* temp = head;
if(temp != NULL) {
while(temp->next != NULL) {
if(temp->next->data == key) {
nodeToDelete = temp->next;
temp->next = temp->next->next;
free(nodeToDelete);
} else {
temp = temp->next;
}
}
}
}
```
```void pop_all(struct Node** head_ref, int key) {
struct Node* nodeToDelete;

//1. if the head is not null and value stored at
//   head is equal to key, keep on adjusting the
//   head as head next and deleting previous head
//   until new head becomes null or not equal to key
while(*head_ref != NULL && (*head_ref)->data == key) {
nodeToDelete = *head_ref;
*head_ref = (*head_ref)->next;
free(nodeToDelete);
}

//2. create a temp node to traverse through the
//   list and delete nodes with value equal to
//   key and adjust links accordingly
struct Node* temp = *head_ref;
if(temp != NULL) {
while(temp->next != NULL) {
if(temp->next->data == key) {
nodeToDelete = temp->next;
temp->next = temp->next->next;
free(nodeToDelete);
} else {
temp = temp->next;
}
}
}
}
```
```def pop_all(self, key):

#1. if the head is not null and value stored at
#   head is equal to key, keep on adjusting the
#   head as head next and deleting previous head
#   until new head becomes null or not equal to key
while(self.head != None and self.head.data == key):
nodeToDelete = self.head
self.head = self.head.next
nodeToDelete = None

#2. create a temp node to traverse through the
#   list and delete nodes with value equal to
#   key and adjust links accordingly
temp = self.head
if(temp != None):
while(temp.next != None):
if(temp.next.data == key):
nodeToDelete = temp.next
temp.next = temp.next.next
nodeToDelete = None
else:
temp = temp.next
```
```void pop_all(int key) {
Node nodeToDelete = new Node();

//1. if the head is not null and value stored at
//   head is equal to key, keep on adjusting the
//   head as head next and deleting previous head
//   until new head becomes null or not equal to key
while(head != null && head.data == key) {
nodeToDelete = head;
head = head.next;
nodeToDelete = null;
}

//2. create a temp node to traverse through the
//   list and delete nodes with value equal to
//   key and adjust links accordingly
Node temp = head;
if(temp != null) {
while(temp.next != null) {
if(temp.next.data == key) {
nodeToDelete = temp.next;
temp.next = temp.next.next;
nodeToDelete = null;
} else {
temp = temp.next;
}
}
}
}
```
```public void pop_all(int key) {
Node nodeToDelete = new Node();

//1. if the head is not null and value stored at
//   head is equal to key, keep on adjusting the
//   head as head next and deleting previous head
//   until new head becomes null or not equal to key
while(head != null && head.data == key) {
nodeToDelete = head;
head = head.next;
nodeToDelete = null;
}

//2. create a temp node to traverse through the
//   list and delete nodes with value equal to
//   key and adjust links accordingly
Node temp = head;
if(temp != null) {
while(temp.next != null) {
if(temp.next.data == key) {
nodeToDelete = temp.next;
temp.next = temp.next.next;
nodeToDelete = null;
} else {
temp = temp.next;
}
}
}
}
```
```public function pop_all(\$key) {
\$nodeToDelete = new Node();

//1. if the head is not null and value stored at
//   head is equal to key, keep on adjusting the
//   head as head next and deleting previous head
//   until new head becomes null or not equal to key
while(\$this->head != null && \$this->head->data == \$key) {
\$nodeToDelete = \$this->head;
\$this->head = \$this->head->next;
\$nodeToDelete = null;
}

//2. create a temp node to traverse through the
//   list and delete nodes with value equal to
//   key and adjust links accordingly
\$temp = \$this->head;
if(\$temp != null) {
while(\$temp->next != null) {
if(\$temp->next->data == \$key) {
\$nodeToDelete = \$temp->next;
\$temp->next = \$temp->next->next;
\$nodeToDelete = null;
} else {
\$temp = \$temp->next;
}
}
}
}
```

The below is a complete program that uses above discussed concept to delete all occurrences of the specified key (if exists) of the linked list.

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

//node structure
struct Node {
int data;
Node* next;
};

class LinkedList {
private:
Node* head;
public:
LinkedList(){
head = NULL;
}

//Add new element at the end of the list
void push_back(int newElement) {
Node* newNode = new Node();
newNode->data = newElement;
newNode->next = NULL;
if(head == NULL) {
head = newNode;
} else {
Node* temp = head;
while(temp->next != NULL)
temp = temp->next;
temp->next = newNode;
}
}

//Delete all nodes by key
void pop_all(int key) {
Node* nodeToDelete;
while(head != NULL && head->data == key) {
nodeToDelete = head;
head = head->next;
free(nodeToDelete);
}

Node* temp = head;
if(temp != NULL) {
while(temp->next != NULL) {
if(temp->next->data == key) {
nodeToDelete = temp->next;
temp->next = temp->next->next;
free(nodeToDelete);
} else {
temp = temp->next;
}
}
}
}

//display the content of the list
void PrintList() {
Node* temp = head;
if(temp != NULL) {
cout<<"\nThe list contains: ";
while(temp != NULL) {
cout<<temp->data<<" ";
temp = temp->next;
}
} else {
cout<<"\nThe list is empty.";
}
}
};

// test the code
int main() {
LinkedList MyList;

//Add five elements at the end of the list.
MyList.push_back(10);
MyList.push_back(20);
MyList.push_back(30);
MyList.push_back(10);
MyList.push_back(20);
MyList.PrintList();

//Delete all occurrences of 20
MyList.pop_all(20);
MyList.PrintList();

return 0;
}
```

The above code will give the following output:

```The list contains: 10 20 30 10 20
The list contains: 10 30 10
```
```#include <stdio.h>
#include <stdlib.h>

//node structure
struct Node {
int data;
struct Node* next;
};

//Add new element at the end of the list
void push_back(struct Node** head_ref, int newElement) {
struct Node *newNode, *temp;
newNode = (struct Node*)malloc(sizeof(struct Node));
newNode->data = newElement;
newNode->next = NULL;
if(*head_ref == NULL) {
*head_ref = newNode;
} else {
temp = *head_ref;
while(temp->next != NULL) {
temp = temp->next;
}
temp->next = newNode;
}
}

//Delete all nodes by key
void pop_all(struct Node** head_ref, int key) {
struct Node* nodeToDelete;
while(*head_ref != NULL && (*head_ref)->data == key) {
nodeToDelete = *head_ref;
*head_ref = (*head_ref)->next;
free(nodeToDelete);
}

struct Node* temp = *head_ref;
if(temp != NULL) {
while(temp->next != NULL) {
if(temp->next->data == key) {
nodeToDelete = temp->next;
temp->next = temp->next->next;
free(nodeToDelete);
} else {
temp = temp->next;
}
}
}
}

//display the content of the list
void PrintList(struct Node* head_ref) {
struct Node* temp = head_ref;
if(head_ref != NULL) {
printf("\nThe list contains: ");
while (temp->next != NULL) {
printf("%i ",temp->data);
temp = temp->next;
}
printf("%i ",temp->data);
} else {
printf("\nThe list is empty.");
}
}

// test the code
int main() {
struct Node* MyList = NULL;

//Add five elements at the end of the list.
push_back(&MyList, 10);
push_back(&MyList, 20);
push_back(&MyList, 30);
push_back(&MyList, 10);
push_back(&MyList, 20);
PrintList(MyList);

//Delete all occurrences of 20
pop_all(&MyList, 20);
PrintList(MyList);

return 0;
}
```

The above code will give the following output:

```The list contains: 10 20 30 10 20
The list contains: 10 30 10
```
```# node structure
class Node:
def __init__(self, data):
self.data = data
self.next = None

#class Linked List
class LinkedList:
def __init__(self):
self.head = None

#Add new element at the end of the list
def push_back(self, newElement):
newNode = Node(newElement)
if(self.head == None):
self.head = newNode
return
else:
temp = self.head
while(temp.next != None):
temp = temp.next
temp.next = newNode

#Delete all nodes by key
def pop_all(self, key):
while(self.head != None and self.head.data == key):
nodeToDelete = self.head
self.head = self.head.next
nodeToDelete = None

temp = self.head
if(temp != None):
while(temp.next != None):
if(temp.next.data == key):
nodeToDelete = temp.next
temp.next = temp.next.next
nodeToDelete = None
else:
temp = temp.next

#display the content of the list
def PrintList(self):
temp = self.head
if(temp != None):
print("\nThe list contains:", end=" ")
while (temp != None):
print(temp.data, end=" ")
temp = temp.next
else:
print("\nThe list is empty.")

# test the code
MyList = LinkedList()

#Add five elements at the end of the list.
MyList.push_back(10)
MyList.push_back(20)
MyList.push_back(30)
MyList.push_back(10)
MyList.push_back(20)
MyList.PrintList()

#Delete all occurrences of 20
MyList.pop_all(20)
MyList.PrintList()
```

The above code will give the following output:

```The list contains: 10 20 30 10 20
The list contains: 10 30 10
```
```//node structure
class Node {
int data;
Node next;
};

class LinkedList {
Node head;

LinkedList(){
head = null;
}

//Add new element at the end of the list
void push_back(int newElement) {
Node newNode = new Node();
newNode.data = newElement;
newNode.next = null;
if(head == null) {
head = newNode;
} else {
Node temp = new Node();
temp = head;
while(temp.next != null)
temp = temp.next;
temp.next = newNode;
}
}

//Delete all nodes by key
void pop_all(int key) {
Node nodeToDelete = new Node();

while(head != null && head.data == key) {
nodeToDelete = head;
head = head.next;
nodeToDelete = null;
}

Node temp = head;
if(temp != null) {
while(temp.next != null) {
if(temp.next.data == key) {
nodeToDelete = temp.next;
temp.next = temp.next.next;
nodeToDelete = null;
} else {
temp = temp.next;
}
}
}
}

//display the content of the list
void PrintList() {
Node temp = new Node();
temp = this.head;
if(temp != null) {
System.out.print("\nThe list contains: ");
while(temp != null) {
System.out.print(temp.data + " ");
temp = temp.next;
}
} else {
System.out.print("\nThe list is empty.");
}
}
};

// test the code
public class Implementation {
public static void main(String[] args) {
LinkedList MyList = new LinkedList();

//Add five elements at the end of the list.
MyList.push_back(10);
MyList.push_back(20);
MyList.push_back(30);
MyList.push_back(10);
MyList.push_back(20);
MyList.PrintList();

//Delete all occurrences of 20
MyList.pop_all(20);
MyList.PrintList();
}
}
```

The above code will give the following output:

```The list contains: 10 20 30 10 20
The list contains: 10 30 10
```
```using System;

//node structure
class Node {
public int data;
public Node next;
};

class LinkedList {
Node head;

public LinkedList(){
head = null;
}

//Add new element at the end of the list
public void push_back(int newElement) {
Node newNode = new Node();
newNode.data = newElement;
newNode.next = null;
if(head == null) {
head = newNode;
} else {
Node temp = new Node();
temp = head;
while(temp.next != null)
temp = temp.next;
temp.next = newNode;
}
}

//Delete all nodes by key
public void pop_all(int key) {
Node nodeToDelete = new Node();

while(head != null && head.data == key) {
nodeToDelete = head;
head = head.next;
nodeToDelete = null;
}

Node temp = head;
if(temp != null) {
while(temp.next != null) {
if(temp.next.data == key) {
nodeToDelete = temp.next;
temp.next = temp.next.next;
nodeToDelete = null;
} else {
temp = temp.next;
}
}
}
}

//display the content of the list
public void PrintList() {
Node temp = new Node();
temp = this.head;
if(temp != null) {
Console.Write("\nThe list contains: ");
while(temp != null) {
Console.Write(temp.data + " ");
temp = temp.next;
}
} else {
Console.Write("\nThe list is empty.");
}
}
};

// test the code
class Implementation {
static void Main(string[] args) {
LinkedList MyList = new LinkedList();

//Add five elements at the end of the list.
MyList.push_back(10);
MyList.push_back(20);
MyList.push_back(30);
MyList.push_back(10);
MyList.push_back(20);
MyList.PrintList();

//Delete all occurrences of 20
MyList.pop_all(20);
MyList.PrintList();
}
}
```

The above code will give the following output:

```The list contains: 10 20 30 10 20
The list contains: 10 30 10
```
```<?php
//node structure
class Node {
public \$data;
public \$next;
}

class LinkedList {
public \$head;

public function __construct(){
\$this->head = null;
}

//Add new element at the end of the list
public function push_back(\$newElement) {
\$newNode = new Node();
\$newNode->data = \$newElement;
\$newNode->next = null;
if(\$this->head == null) {
\$this->head = \$newNode;
} else {
\$temp = new Node();
\$temp = \$this->head;
while(\$temp->next != null) {
\$temp = \$temp->next;
}
\$temp->next = \$newNode;
}
}

//Delete all nodes by key
public function pop_all(\$key) {
\$nodeToDelete = new Node();
while(\$this->head != null && \$this->head->data == \$key) {
\$nodeToDelete = \$this->head;
\$this->head = \$this->head->next;
\$nodeToDelete = null;
}

\$temp = \$this->head;
if(\$temp != null) {
while(\$temp->next != null) {
if(\$temp->next->data == \$key) {
\$nodeToDelete = \$temp->next;
\$temp->next = \$temp->next->next;
\$nodeToDelete = null;
} else {
\$temp = \$temp->next;
}
}
}
}

//display the content of the list
public function PrintList() {
\$temp = new Node();
\$temp = \$this->head;
if(\$temp != null) {
echo "\nThe list contains: ";
while(\$temp != null) {
echo \$temp->data." ";
\$temp = \$temp->next;
}
} else {
echo "\nThe list is empty.";
}
}
};

// test the code
\$MyList = new LinkedList();

//Add five elements at the end of the list.
\$MyList->push_back(10);
\$MyList->push_back(20);
\$MyList->push_back(30);
\$MyList->push_back(10);
\$MyList->push_back(20);
\$MyList->PrintList();

//Delete all occurrences of 20
\$MyList->pop_all(20);
\$MyList->PrintList();
?>
```

The above code will give the following output:

```The list contains: 10 20 30 10 20
The list contains: 10 30 10
```