Handling Unknown user input in C

Question

Circular Queue in C

Currently working on a code that gives us an integer value (1,2,3) along side with a datatype either integer/char/string. Here,

1 -> Enqueue
2 -> Dequeue
3 -> Display

For different testcases i am given with different data types. Like testcase 1 has integer values and testcase 2 with string names.

I need help in handling all the different input types for C. The following is my code for simple integer values.

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

struct node{
    int data;
    struct node *next;
};

struct node *head, *tail = NULL;

void enq(int x){
    struct node *nade = malloc(sizeof(struct node));
    nade->data = x;
    nade->next = head;
    if (head == NULL)
        head = tail = nade;
    else{
        tail->next = nade;
        tail = nade;
    }
}

void dq(){
    struct node *temp;
    if (head == NULL)
        printf("Deque is Empty\n");
    else if (head == tail){
        printf("%d is deleted\n", head->data);
        head = NULL;
    }
    else{
        printf("%d is deleted\n", head->data);
        tail->next = head->next;
        head = head->next;
    }
}

void display(){
    if (head == NULL)
        printf("Empty\n");
    else{
        struct node *temp;
        printf("Circular Queue ");
        for (temp = head; temp != tail; temp = temp->next)
            printf("%d ", temp->data);
        printf("%d\n", temp->data);
    }
}

int main(){
    int t; scanf("%d", &t);
    do{
        switch (t)
        {
        int x;
        case 1:
            scanf("%d", &x);
            enq(x);
            break;
        case 2:
            dq();
            break;
        case 3:
            display();
            break;
        }
        scanf("%d", &t);
    }while (t != 4);
    return 0;
}