LinkedList

#include<iostream>

using namespace std;

struct elem {
  int key;
  elem * next;
}* start;

void init();
void add_b(int n);
void add_mid1(int n, int k);
void add_mid2(int n, int k);
void add_e(int n);
int del_b(int & n);
int del_mid1(int & n, int k);
int del_mid2(int & n, int k);
int del_e(int & n);
int search_iter(int n);
void list();
void destroy(elem *&listt);
void addtolist(int array[], int l, elem *&s);
void add_e(elem *&s, int n);

int main() {
  int num, k, ch;
  init();
  do {
    cout << "\n Menu \n";
    cout << "1. Add the first element\n";
    cout << "2. Add element before k\n";
    cout << "3. Add element after k\n";
    cout << "4. Add the last element\n";
    cout << "5. Del the first element\n";
    cout << "6. Del element before k\n";
    cout << "7. Del element after k \n";
    cout << "8. Del the last element\n";
    cout << "9. Search element\n";
    cout << "10. Show the list\n";
    cout << "11. Destroy the list\n";
    cout << "12. Add to list\n";
    cout << "0. Exit\n";
    cout << "Your choice:";
    cin >> ch;
    switch (ch) {
    case 1:
      cout << "num=";
      cin >> num;
      add_b(num);
      break;
    case 2:
      cout << "num=";
      cin >> num;
      cout << "k=";
      cin >> k;
      add_mid1(num, k);
      break;
    case 3:
      cout << "num=";
      cin >> num;
      cout << "k=";
      cin >> k;
      add_mid2(num, k);
      break;
    case 4:
      cout << "num=";
      cin >> num;
      add_e(num);
      break;
    case 5:
      if (del_b(num))
        list();
      break;
    case 6:
      cout << "num=";
      cin >> num;
      cout << "k=";
      cin >> k;
      if (del_mid1(num, k))
        list();
      break;
    case 7:
      cout << "num=";
      cin >> num;
      cout << "k=";
      cin >> k;
      if (del_mid2(num, k))
        list();
      break;
    case 8:
      if (del_e(num))
        list();
      break;
    case 9:
      cout << "num=";
      cin >> num;
      if (search_iter(num))
        cout << "\n" << num << " is found!\n";
      else
        cout << "\n " << num << " is not found!\n";
      break;
    case 10:
      list();
      break;
    case 11:
        destroy(start);
        break;
    case 12:
        {
            int array[10] = { 10, 20, 30, 55, 66, 20, 54, 554, 534, 5325};

            addtolist(array, 10, start);
        }
        break;
    }
  } while (ch != 0);
  return 0;
  system("pause");
}

void add_e(elem *&s, int n)
{
  elem *p = s, *q = s;
  q = new elem;
  q->key = n;
  q->next = NULL;
  if (s)
  {
    while (p -> next)
      p = p -> next;
    p -> next = q;
  } else
    s = q;
}

void addtolist(int array[], int l, elem *&s)
{
    for (int i = 0; i < l; i++)
    {
        add_e(s, array[i]);
    }
}

void destroy(elem *&listt)
{
    while (listt)
    {
        elem *t = listt;
        cout << "Deleting: " << listt->key << endl;
        listt = listt->next;
        delete t;
    }
}

void init() {
  start = NULL;
}
void add_b(int n) {
  elem * p = start;
  start = new elem;
  start -> key = n;
  start -> next = p;
}

void add_mid1(int n, int k) {
  elem * q = NULL, * p = start;
  while (p -> key != k)
    p = p -> next;
  q = new elem;
  q -> next = p -> next;
  q -> key = p -> key;
  p -> next = q;
  p -> key = n;
}

void add_mid2(int n, int k) {
  elem * q = NULL, * p = start;
  while (p -> key != k)
    p = p -> next;
  q = new elem;
  q -> next = p -> next;
  q -> key = n;
  p -> next = q;
}

void add_e(int n) {
  elem * p = start, * q = start;
  q = new elem;
  q -> key = n;
  q -> next = NULL;
  if (start) {
    while (p -> next)
      p = p -> next;
    p -> next = q;
  } else
    start = q;
}

int del_b(int & n) {
  elem * p = start;
  if (start) {
    n = start -> key;
    start = start -> next;
    delete p;
    return 1;
  } else
    return 0;
}

int del_mid1(int & n, int k) {
  elem * q = NULL, * p = start;
  if (start) {
    while (p -> key != k) {
      q = p;
      p = p -> next;
    }
    n = q -> key;
    q -> next = p -> next;
    q -> key = p -> key;

    delete p;
    return 1;
  } else
    return 0;
}

int del_mid2(int & n, int k) {
  elem * q = NULL, * p = start;
  if (start) {
    while (p -> key != k)
      p = p -> next;
    q = p -> next;
    n = q -> key;

    p -> next = q -> next;
    delete q;
    return 1;
  } else
    return 0;
}

int del_e(int & n) {
  elem * q = NULL, * p = start;
  if (start) {
    if (p -> next) {
      while (p -> next) {
        q = p;
        p = p -> next;
      }
      q -> next = NULL;
    } else
      start = NULL;
    n = p -> key;
    delete p;
    return 1;
  } else
    return 0;
}

int search_iter(int n) {
  elem * p = start;
  if (start) {
    while ((p -> key != n) && (p -> next))
      p = p -> next;
    if (p -> key == n)
      return 1;
    else
      return 0;
  }
  return 0;
}

void list()
{
    elem *p = start;
    if (start)
    while (p)
    {
        cout << p->key << "\t";
        p = p->next;
    }
    cout << "\n\n";
}