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#include <stdio.h>
#include <stdlib.h>
struct node{
	int data;
	struct node *link;
};

struct node *head;
struct node *temp;

struct node *head = NULL;

struct node *create(struct node *head){ 
    struct node *temp;
	struct node *new;
	int data;
	    printf("Enter data (-1 to stop): ");
        scanf("%d", &data);
    
    while (data != -1) {  // Accept values until user enters -1
        new = (struct node*)malloc(sizeof(struct node));
        if (new == NULL) {
            printf("Memory allocation failed!\n");
            return head;
        }
        new->data = data;
        new->link = NULL;

        if (head == NULL) {  
            head = new;  // First node
            temp = head;
        } else {
            temp->link = new;
            temp = new;
        }

        printf("Enter data (-1 to stop): ");
        scanf("%d", &data);
    }
    return head;
}
    void display(struct node *head){
        struct node *temp;
        temp = head;
        if(temp == NULL){
        	printf("No list Found!");
		}	
		else{
			while(temp->link != NULL){
			printf("%d->", temp->data);
			temp = temp->link;
		}
		temp->link = NULL;
    }
}
 void alternate(struct node *head){
 	struct node *temp;
 	temp = head;
        if(temp == NULL){
        	printf("No list Found!");
		}	
		else{
			while(temp->link != NULL){
			printf("%d->", temp->data);
			temp = temp->link->link;
		}
		temp->link = NULL;
    }
 }
// void InsertAtBegin(struct node *head){
// 	struct node *temp , *new;
// 	new = (struct node *)malloc(sizeof(struct node));
// 	printf("enter data:");
// 	scanf("%d",&new->data);
// 	// 	new->data=data;
// 	new->link = head;
// 	head=new;
//    //return head;
// }

    int main(){
    	int ch; 
    	printf("Enter choice: ");
    	do{
    		printf("1.create:\n");
            printf("2.display:\n");
            printf("3.alternate:\n");
            printf("4.InsertAtBegin:\n");
			printf("0.exit:\n");
			scanf("%d", &ch);
		switch(ch)
	{
		case 1:
		   head = create(head);
	       break;
		case 2:
		  display(head);
		  break; 
		case 3:
		  alternate(head);
		  break;
		case 4:
			InsertAtBegin(head);
			break;
		case 0:
	      printf("Exiting...\n");
	   	  break;
	    Default:
		  Printf("Invalid option:");	
		  break;	
		}
	}	while(ch!=0);
return 0;
}