Modify the following insert functions of this code and implement a logic that user will not be able to add same value again for exam one he enter 5 he will not be able to add 5 again

Modify the following insert functions of this code and implement a logic that user will not be able to add same value again for exam one he enter 5 he will not be able to add 5 again

#include<iostream>
#include<cstdio>
#include<cstdlib>
using namespace std;
/*
 * Node Declaration
 */
class node
{
     public:
    int info;
     node *next;
}*start;

/*
 * Class Declaration
 */
class single_llist
{
    public:
        node* create_node(int);
        void insert_begin();
        void insert_pos();
        void insert_last(); 
        void delete_pos();
        void sort();
        void search();
        void update();
        void reverse();
        void display();
        single_llist() 
        {
            start = NULL;
        }
};

/*
 * Main :contains menu 
 */
main()
{
    int choice, nodes, element, position, i;
    single_llist sl;
    start = NULL;
    while (1)
    {
        cout<<endl<<"Operations on singly linked list"<<endl;
        cout<<endl<<"---------------------------------"<<endl;
        cout<<"1.Insert Node at beginning"<<endl;
        cout<<"2.Insert node at last"<<endl;
        cout<<"3.Insert node at position"<<endl;
        cout<<"4.Update Node Value"<<endl;
        cout<<"5.Search Element"<<endl;
        cout<<"6.Display Linked List"<<endl;
        cout<<"7.Exit "<<endl;
        cout<<"Enter your choice : ";
        cin>>choice;
        switch(choice)
        {
        case 1:
            cout<<"Inserting Node at Beginning: "<<endl;
            sl.insert_begin();
            cout<<endl;
            break;
        case 2:
            cout<<"Inserting Node at Last: "<<endl;
            sl.insert_last();
            cout<<endl;
            break;
        case 3:
            cout<<"Inserting Node at a given position:"<<endl;
            sl.insert_pos();
            cout<<endl;
            break;
        case 4:
            cout<<"Update Node Value:"<<endl;  
            sl.update();
            cout<<endl;
            break;
        case 5:
            cout<<"Search element in Link List: "<<endl;
            sl.search();
            cout<<endl;
            break;
        case 6:
            cout<<"Display elements of link list"<<endl;
            sl.display();
            cout<<endl;
            break;
        case 7:
            cout<<"Exiting..."<<endl;
            exit(1);
            break;  
        default:
            cout<<"Wrong choice"<<endl;
        }
    }
}

/*
 * Creating Node
 */
node *single_llist::create_node(int value)
{
    class  node *temp, *s;
    temp = new(class  node); 
    if (temp == NULL)
    {
        cout<<"Memory not allocated "<<endl;
        return 0;
    }
    else
    {
        temp->info = value;
        temp->next = NULL;     
        return temp;
    }
}

/*
 * Inserting element in beginning
 */
void single_llist::insert_begin()
{
    int value;
    cout<<"Enter the value to be inserted: ";
    cin>>value;
    class  node *temp, *p;
    temp = create_node(value);
    if (start == NULL)
    {
        start = temp;
        start->next = NULL;          
    } 
    else
    {
        p = start;
        start = temp;
        start->next = p;
    }
    cout<<"Element Inserted at beginning"<<endl;
}

/*
 * Inserting Node at last
 */
void single_llist::insert_last()
{
    int value;
    cout<<"Enter the value to be inserted: ";
    cin>>value;
    class  node *temp, *s;
    temp = create_node(value);
    s = start;
    while (s->next != NULL)
    {         
        s = s->next;        
    }
    temp->next = NULL;
    s->next = temp;
    cout<<"Element Inserted at last"<<endl;  
}

/*
 * Insertion of node at a given position
 */
void single_llist::insert_pos()
{
    int value, pos, counter = 0; 
    cout<<"Enter the value to be inserted: ";
    cin>>value;
    class  node *temp, *s, *ptr;
    temp = create_node(value);
    cout<<"Enter the postion at which node to be inserted: ";
    cin>>pos;
    int i;
    s = start;
    while (s != NULL)
    {
        s = s->next;
        counter++;
    }
    if (pos == 1)
    {
        if (start == NULL)
        {
            start = temp;
            start->next = NULL;
        }
        else
        {
            ptr = start;
            start = temp;
            start->next = ptr;
        }
    }
    else if (pos > 1  && pos <= counter)
    {
        s = start;
        for (i = 1; i < pos; i++)
        {
            ptr = s;
            s = s->next;
        }
        ptr->next = temp;
        temp->next = s;
    }
    else
    {
        cout<<"Positon out of range"<<endl;
    }
}

/*
 * Update a given Node
 */