I have implemented a Queue using singly linked list

Queue_implementation_using_singly_linkedlist.c

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

struct node 
{
    int data;
    struct node* link;
};
struct node *rear = NULL;
struct node *front= NULL;
void push (int x )
{
	
	struct node* temp = (struct node*)malloc(sizeof(struct node));
	if (!temp)
	{
	    printf("Sorry:/ We cannot allocate memory");
	    return;
	}
	
	printf("Enter element bossyyyy which you want to push\n");
	
	scanf("%d", &x);
	temp->data = x;
	temp->link = NULL;
	if(front == NULL && rear == NULL)
	{
	    front = rear = temp;
	    return;
	}   
	rear->link = temp;
	rear = temp;
}
int pop()
{
    struct node* temp = front;
    if (front == NULL && rear == NULL)
    {
    printf("Sorry!!! Queue is empty. We have nothing to pop\n");
    return 0;
    }
    if (front == rear)
    {
        front = rear = NULL;
    }
    else 
    {
        front = front->link;
        free(temp);
    }
}	
void display()
{
    struct node *temp = front;
    temp = front;
    if (front == NULL && rear ==NULL)
    {
        printf("Awwww queue is empty\n");
        return;
    }
     while(temp!= NULL)
    {
        printf("%d  ",temp->data);
        temp = temp->link;
    }
     printf("\n");
}
	
int main()
{

    int choose_number, e;
    while(1)
    {
        printf("1. Push element\n");
        printf("2. Pop element\n");
        printf("3. Display elements\n");
        printf("Choose a number my dear friend\n");
        scanf("%d", &choose_number);
        switch (choose_number)
        {
        case 1: push(e);
                break;
        case 2: e = pop();
                printf("e => %d\n", e);
                break;
        case 3: display();
                break;
    
        default: printf(" You have an Invalid choice\n");
        }
    }
    return 0;
    
}