Insertion in Linked List

#include<iostream>
#include<stdio.h>
#include<stdlib.h>

using namespace std;

struct node
{
    int data;
    struct node *link;
};
struct node *start = NULL; //declaring a head pointer

struct node* createNode() // allocating memory to a node
{
    struct node *n;
    n = (struct node *)malloc(sizeof(struct node));
    return n;
}
void insertNodeAtEnd()
{
    struct node *temp;
    temp = createNode();
    cout << "Enter a number : ";
    cin >> temp->data;
    temp->link = NULL;
    if(start==NULL){ // when the list is empty
        start = temp;
    }
    else{
        struct node *t = start;
        while(t->link!=NULL){
            t = t->link;
        }
        t->link = temp;
    }
    cout << "\nElement inserted.\n\n";
}
void insertNodeAtBeg()
{
    struct node *temp;
    temp = createNode();
    cout << "Enter a number : ";
    cin >> temp->data;
    temp->link = NULL;
    if(start==NULL){
        start = temp;
    }
    else{
        struct node *t;
        t = temp;
        temp->link = start;
        start = temp;
    }
    cout << "\nElement inserted.\n\n";
}
void insertAfter()
{
    if(start==NULL){
        cout << "\nList is empty. Create List First.\n";
    }
    else {
        int node;
        struct node *temp;
        temp = createNode();
        cout << "Enter the number you want to insert : ";
        cin >> temp->data;
        temp->link = NULL;
        cout << "Enter the node after you want to insert : ";
        cin >> node;
        struct node *t = start;
        while(t->data!=node&&t->link!=NULL){ // for finding the node
            t = t->link;
        }
        if(t->link==NULL){ //when the node is present at the beginning
            t->link = temp;
        }
        else {
            temp->link = t->link;
            t->link = temp;
        }
        cout << "\nElement inserted.\n\n";
    }
}
void insertBefore()
{
    if(start==NULL){
        cout << "\nList is empty. Create List First.\n";
    }
    else {
        int node;
        struct node *temp;
        temp = createNode();
        cout << "Enter the number you want to insert : ";
        cin >> temp->data;
        temp->link = NULL;
        cout << "Enter the node before you want to insert : ";
        cin >> node;
        struct node *t = start,*p = start;
        while(t->data!=node){
            if(t==p){
                t = t->link;
            }
            else {
                t = t->link;
                p = p->link;
            }
        }
        if(t==p){ // when the node is present at beginning, both t and p pointers point to same node
            temp->link = t;
            start = temp;
        }
        else {
            temp->link = t;
            p->link = temp;
        }
        cout << "\nElement inserted.\n\n";
    }
}
void displayList(struct node *n)
{
    struct node *t;
    if(start==NULL){
        cout << "\nList is empty.\n\n";
    }
    else {
        t = start;
        while(t!=NULL){
            cout << t->data << " ";
            t = t->link;
        }
    }
    cout << "\n\n";
}
int menu()
{
    int ch;
    cout << "1. Insert an element at the end.\n";
    cout << "2. Insert an element at the beginning.\n";
    cout << "3. Insert an element after a node.\n";
    cout << "4. Insert an element before a node.\n";
    cout << "5. Display List.\n";
    cout << "6. Exit\n";
    cout << "Enter your choice : ";
    cin >> ch;
    return ch;
}
int main()
{
    while(1)
    {
        switch(menu())
        {
        case 1:
            insertNodeAtEnd();
            break;
        case 2:
            insertNodeAtBeg();
            break;
        case 3:
            insertAfter();
            break;
        case 4:
            insertBefore();
            break;
        case 5:
            displayList(start);
            break;
        case 6:
            exit(0);
            break;
        default:
            cout << "\nInvalid choice\n\n";
        }
    }
}