User input linked list - c++

Question

I'm trying to get user input to insert element in the linked list. It works if I try to add at 1st or 2nd position. Even though list has more than 3 element, if I put 3 in it, it never works and returns nothing showing no syntax error. Is it wrong use with variable or loop. I'm super confused.
#include<stdlib.h>
#include<stdio.h>
struct Node
{
int data;
Node *next;
};
Node *head;
void insert(int data, int n)
{
Node* temp1 = new Node;
temp1->data = data;
temp1->next = NULL;
if(n == 1)
{
temp1->next = head;
head = temp1;
return;
}
else{
Node *temp2 = head;
for(int i = 0; i = n - 2; i++)
{
temp2 = temp2->next;
}
temp1->next = temp2->next;
temp2->next = temp1;
return;
}
}
void print()
{
Node *temp = head;
while(temp != NULL)
{
printf("%d ", temp->data);
temp = temp->next;
}
}
int main()
{
head = NULL;
insert(3, 1);
insert(33, 1);
insert(384, 2);
insert(384, 1);
insert(432, 3);
insert(34, 4);
print();
}

Answer 1

The obvious mistakes have been already elaborated in the comment. Something additional.
If this is intended to be C++, then you should also use C++ language, especially classes.
Then from your design. Please do not mix up the "Node" with the "Linked List". A node is a part of a linked list. It is contained within the linked list. And it should not be exposed to the outside world.
I you want to read a little bit about needed functionality of a linked list, then you may check the CPP reference. For example here
And an example, from which you can take more ideas is listed below.
But first you need to read a book, this thing made out of real paper :-)
#include <iostream>
#include <iterator>
#include <initializer_list>
#include <algorithm>
// Very simple implementation of a forward list
template <class T>
class SinglyLinkedList {
// The node
struct Node {
T data{}; // Data. Would normally be a templated argument
Node* next{}; // And the pointer to the next node
Node(const T& i, Node* n = nullptr) : data(i), next(n) {}; // Simple constructor to set a value and next pointer
};
Node* head{}; // This is the start of the list
// It would be advisable to have a tail pointer. We use the more inefficient approach here
Node* getLast() const { Node* n{ head }; while (n and n->next) n = n->next; return n; }
public:
// Constructor / Destructor --------------------------------------------------------------------------------------------------------
~SinglyLinkedList() { clear(); }
// Default constuctor
SinglyLinkedList() {} // Default
// From an initialization list
SinglyLinkedList(const std::initializer_list<T>& il) { clear(); for (const T& i : il) push_back(i); } // From initializer list
// Copy constructor
SinglyLinkedList(const SinglyLinkedList& other) { clear(); for (const T& i : other) push_back(i); }
// Move constructor. Will steal the elements from the other
SinglyLinkedList(SinglyLinkedList&& other) noexcept { head = other.head; other.head = nullptr; }
// Assignment operator
SinglyLinkedList& operator = (const SinglyLinkedList& other) { clear(); for (const T& i : other) push_back(i); }
// Move assignment operator
SinglyLinkedList& operator = (SinglyLinkedList&& other) { head = other.head; other.head = nullptr; }
// Housekeeping --------------------------------------------------------------------------------------------------------------
void clear() { Node* tmp{ head }; while (tmp) { Node* toDelete{ tmp }; tmp = tmp->next; delete toDelete; } head = nullptr; }
int empty() const { return head == nullptr; }
int size() const { int k{}; Node* n{ head }; while (n) { ++k; n = n->next; } return k; }
// Modify content --------------------------------------------------------------------------------------------------------------
void push_front(const T& i) { Node* n = new Node(i); n->next = head; head = n; };
void push_back(const T& i) { Node* n = new Node(i); Node* l = getLast(); if (l) l->next = n; else head = n; }
void pop_front() { if (head) { Node* tmp = head->next; delete head; head = tmp; } }
void pop_back() { // This is a little bit more difficult in a singly linked list
if (head) {
Node* n{ head }, * previous{};
while (n and n->next) {
previous = n;
n = n->next;
}
delete n;
if (previous)
previous->next = nullptr;
else
head->next = nullptr;
}
}
// Access elements --------------------------------------------------------------------------------
T& front() const { return head ? head->data : 0; };
T back() const { Node* n = getLast(); return n ? n->data : 0; }
// Add iterator properties to class ---------------------------------------------------------------
struct iterator { // Local class for iterator
Node* iter{}; // Iterator is basically a pointer to the node
// Define alias names necessary for the iterator functionality
using iterator_category = std::forward_iterator_tag;
using difference_type = std::ptrdiff_t;
using value_type = T;
using pointer = T*;
using reference = T&;
// Constructor
iterator() {}
iterator(Node* n) : iter(n) {}
// Dereferencing
reference operator *() const { return iter->data; }
pointer operator ->() const { return &iter->data; }
// Aithmetic operations
iterator& operator ++() { if (iter) iter = iter->next; return *this; }
iterator operator ++(int) { iterator temp{ *this }; ++* this; return temp; }
iterator operator +(const difference_type& n) const { iterator temp{ *this }; difference_type k{ n }; while (k--)++temp; return temp; }
iterator& operator +=(const difference_type& n) { difference_type k{ n }; while (k--)++* this; return *this; };
// Comparison
bool operator != (const iterator& other) const { return iter != other.iter; }
bool operator == (const iterator& other) const { return iter == other.iter; }
bool operator < (const iterator& other) const { return iter < other.iter; }
bool operator > (const iterator& other) const { return iter > other.iter; }
bool operator <= (const iterator& other) const { return iter <= other.iter; }
bool operator >= (const iterator& other) const { return iter >= other.iter; }
// Difference. Also complicated, because no random access
difference_type operator-(const iterator& other) const {
difference_type result{};
Node* n{ iter };
while (n and n != other.iter) {
++result;
n = n->next;
}
return result;
}
};
// Begin and end function to initialize an iterator
iterator begin() const { return iterator(head); }
iterator end() const { return iterator(); }
// Functions typcical for forward lists ----------------------------------------------------------------------
// Easy, becuase we can operate form the current iterator and do not need the "previous" element
iterator insertAfter(iterator& pos, const T& i) {
iterator result{};
if (pos.iter and pos.iter->next) {
Node* n = new Node(i, pos.iter->next);
pos.iter->next = n;
result = n;
}
return result;
}
iterator eraseAfter(iterator& pos) {
iterator result{};
if (pos.iter and pos.iter->next) {
Node* tmp = pos.iter->next->next;
delete pos.iter->next;
pos.iter->next = tmp;
result = pos.iter->next;
}
return result;
}
};
// Test/Driver Code
int main() {
// Example for initilizer list
SinglyLinkedList<int> sllbase{ 5,6,7,8,9,10,11,12,13,14,15 };
// Show move constructor
SinglyLinkedList<int> sll(std::move(sllbase));
// Add some values in the front
sll.push_front(4);
sll.push_front(3);
sll.push_front(2);
sll.push_front(1);
// Delete 1st element (Number 1)
sll.pop_front();
// Delete last element
sll.pop_back();
// Use a std::algorithm on our custom linked list. Works because we have an interator
SinglyLinkedList<int>::iterator iter = std::find(sll.begin(), sll.end(), 8);
// Now add an element after 8
iter = sll.insertAfter(iter, 88);
// End delete the 9
iter = sll.eraseAfter(iter);
// Use range based for loop. Works because, we have iterators
for (int i : sll)
std::cout << i << ' ';
return 0;
}

Answer 2

Your mistake is in this for loop
for(int i = 0; i = n - 2; i++)
There is assignment operator(=) instead of equal to operator(==), also logic is wrong.
This is how it should be
#include<cstdlib>
#include<cstdio>
struct Node
{
int data;
Node *next;
};
Node *head;
void insert(int data, int n)
{
Node* temp1 = new Node;
temp1->data = data;
temp1->next = NULL;
if(n == 1)
{
temp1->next = head;
head = temp1;
return;
}
else{
Node *temp2 = head;
for(int i = 1; i < n - 1; i++)
{
temp2 = temp2->next;
}
temp1->next = temp2->next;
temp2->next = temp1;
return;
}
}
void print()
{
Node *temp = head;
while(temp != NULL)
{
printf("%d ", temp->data);
temp = temp->next;
}
}
int main()
{
head = nullptr;
insert(3, 1);
insert(33, 1);
insert(384, 2);
insert(384, 1);
insert(432, 3);
insert(34, 4);
print();
}