Pointers in Linked List [closed] - c++

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I'm new to C++, so my code is not optimal, but at the moment I just want it to work.
I have to write a function that compares every 2 elements (1. and 2., 2. and 3. etc.) of linked list and deletes the first of these two elements if it's smaller than the next one. At the end I have to display the list adter editing. I found some examples of what I'm trying to do, but they make me confused and I have no idea how to adjust them to my case.
Here is my code:
#include <iostream>
#include <cstdlib>
using namespace std;
struct elements {
int value;
elements * next;
};
void f (elements * & start){
if (start == NULL || start -> next == NULL) {
return;
}
elements * p = start, * prevvalue = NULL, * previous = NULL, * del, * before = NULL, * after = NULL;
int first = start -> value;
int second = 0;
for (; p != NULL; p = p -> next){
cout << p -> value << endl;
second = p -> value;
if (first < (p -> value)) {
before = prevvalue;
del = p;
previous = p;
p -> next = after -> next;
after -> next = p;
delete del;
}
first = second;
previous = prevvalue;
}
if (previous == NULL) start = start -> next;
else prevvalue -> next = start -> next;
}
int main (){
elements * start = NULL, * last = NULL, * input;
int count;
cout << "How many elmenets would you like to input? ";
cin >> count;
for (int i = 0; i < count; i++){
cout << "Please input " << i + 1 << ". element: ";
elements * input = new elements;
cin >> input -> value;
input -> next = NULL;
if (last != NULL) {
last -> next = input;
last = input;
}
else start = last = input;
}
f (start);
elements * p = start;
while (p != NULL) {
cout << p -> value << endl;
p = p -> next;
}
input = start;
while (start != NULL){
elements * temp = start;
start = start -> next;
delete temp;
}
return 0;
}
There's something totally wrong with pointers, so it's not working.
Can someone please edit my code and throw out everything that's unnecessary?
Thank you in advance!

Answer 1

After some cleanup something like this
#include <iostream>
#include <cstdlib>
using namespace std;
struct elements {
int value;
elements* next;
};
elements* funkcija(elements *start) {
if (start == NULL || start->next == NULL) {
return start;
}
elements *list = start;
elements *current = start;
elements *previous = nullptr;
while(current) {
elements* next = current->next;
if (!next) {
break;
}
if (current->value < next->value) {
if (previous) {
delete current;
previous->next = next;
}
else {
list = next;
delete current;
}
current = nullptr;
}
else {
previous = current;
}
current = next;
}
return list;
}
int main() {
elements *start = NULL, *last = NULL;
int count;
cout << "How many elmenets would you like to input? ";
cin >> count;
for (int i = 0; i < count; i++) {
cout << "Please input " << i + 1 << ". element: ";
elements* input = new elements;
cin >> input->value;
input->next = NULL;
if (last != NULL) {
last->next = input;
last = input;
}
else {
start = last = input;
}
}
start = funkcija(start);
elements * p = start;
while (p != NULL) {
cout << p->value << endl;
p = p->next;
}
while (start != NULL) {
elements * temp = start;
start = start->next;
delete temp;
}
return 0;
}