Linked List

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

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

struct node *start = NULL;

void insertAtStart() {
    struct node *temp = (struct node*)malloc(sizeof(struct node));
    printf("Enter some data\n");
    scanf("%d", &temp->data);
    temp->next = start;
    start = temp;
}

void insertAtLast() {
    //create a node
    struct node *temp = (struct node*)malloc(sizeof(struct node));
    temp -> next = NULL;
    printf("Enter some data\n");
    scanf("%d", &temp->data);
    if(start == NULL)
    start = temp;
    else {
        struct node*x= start;
        while(x->next!=NULL)
        x=x->next;
        x->next = temp;
    }
}

void insertAfter(int k) {
    struct node *temp = (struct node*)malloc(sizeof(struct node));
    printf("Enter some data\n");
    scanf("%d", &temp->data);
    struct node *x=start;
    while(x!=NULL && x->data!=k ) {
        x=x->next;
    }
    if(x != NULL) {
        temp->next = x->next;
        x->next = temp;
    }
    else
    printf("Data not found");

}

void insertBefore(int k) {
    struct node *temp = (struct node*)malloc(sizeof(struct node));
    printf("Enter some data\n");
    scanf("%d", &temp->data);
    struct node *x=start;
    struct node *y=NULL;
    while(x!=NULL && x->data!=k ) {
        y=x;
        x=x->next;
    }
    if(x != NULL) {
        if(y==NULL) {
            temp->next = start;
            start = temp;
        }
        else {
            y->next = temp;
            temp->next = x;
        }
    }
    else
    printf("Data not found");
}

void display() {
    if(start == NULL) printf("Empty Linked List");
    else {
        struct node*x=start;
        while(x!=NULL) {
            printf("%d ", x->data);
            x=x->next;
        }
    }

}

void DeleteFirst() {
    if(start!=NULL)
    start = start-> next;
    else
    printf("Already Empty");
}

void DeleteLast() {
    if(start!=NULL) {
        struct node *q=NULL;
        struct node *p=start;
        while(p->next!=NULL) {
            q = p;
            p = p->next;
        }
        if(q!=NULL)
        {
            q->next=NULL;
        }
        else
        {
            start = NULL;
        }
        }
}

void deleteByValue(int m) {
    if(start==NULL) {
        printf("Empty Array");
    }
    else {
        struct node *p = start;
        struct node *q = NULL;
        while(p->data!=m) {
            q=p;
            p=p->next;
        }
        if(p==NULL)
            printf("Element not Found.\n");
        else if(q==NULL)
            start = p->next;
        else
            q->next = p->next;
    }
}

void reverse() {
    struct node *p=start;
    struct node *r= NULL;
    struct node *q= NULL;
    do {
        r=q;
        q=p;
        if(p!=NULL) {
            p=p->next;
            q->next=r;
        }
        else {
            printf("Empty List!");
        }
    }
    while (p!=NULL);

    start = q;
}


main() {
    int c=0;
    do {
        printf("\n\nMenu:\n--------------------\n");
        printf("Display: 1\nInsert at Last: 2\nInsert at Start: 3\nInsert element at a certain position: 4\nInsert element before a certain element: 5\n");
        printf("Delete First: 6\n");
        printf("Delete Last: 7\n");
        printf("Delete By Value: 8\n");
        printf("Reverse: 9\n");
        printf("Exit: 10\n");
        scanf("%d", &c);
        switch(c) {
            case 1:
            display();
            break;
            case 2:
            insertAtLast();
            break;
            case 3:
            insertAtStart();
            break;
            case 4:
            printf("Enter the element after which data has to be inserted.\n");
            int k;
            scanf("%d", &k);
            insertAfter(k);
            break;
            case 5:
            printf("Enter the element before which data has to be inserted.\n");
            int l;
            scanf("%d", &l);
            insertBefore(l);
            break;
            case 6:
                DeleteFirst();
                break;
            case 7:
                DeleteLast();
                break;
            case 8:
                printf("Enter the value:\n");
                int m;
                scanf("%d", &m);
                deleteByValue(m);
                break;
            case 9:
                reverse();
                break;
            case 10:
            printf("Breaking out of the loop");
        }
    }
    while(c!=10);
}