C program to insert an element at any position in a linked list

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

/* Node Stucture */
typedef struct node_t {
int data;
struct node_t *next;
} Node;

/* Function Declarations */
Node * insert_top(int, Node *);
Node * insert_bottom(int, Node *);
Node * insert_after(int, int, Node *);
Node * insert_before(int, int, Node *);
void print(Node *);
int count(Node *);

/* Add a new node to the top of a list */
Node * insert_top(int num, Node *head) {
Node *new_node;
new_node = (Node *) malloc(sizeof(Node));
new_node->data = num;
new_node->next= head;
head = new_node;
return head;
}

/* Add a new node to the bottom of a list */
Node * insert_bottom(int num, Node *head) {
Node *current_node = head;
Node *new_node;
while ( current_node != NULL && current_node->next != NULL) {
current_node = current_node->next;
}

new_node = (Node *) malloc(sizeof(Node));
new_node->data = num;
new_node->next= NULL;
if (current_node != NULL)
current_node->next = new_node;
else
head = new_node;
return head;
}

/* Add a new node after an element in the list */
Node * insert_after(int num, int prev_num, Node *head) {
Node *current_node = head;
Node *new_node;
while ( current_node->data != prev_num) {
current_node = current_node->next;
}
new_node = (Node *) malloc(sizeof(Node));
new_node->data = num;
new_node->next= current_node->next;
current_node->next = new_node;
return head;
}

/* Add a new node before an element in the list */
Node * insert_before(int num, int next_num, Node *head) {
Node *current_node = head;
Node *new_node;
while ( current_node->next->data != next_num) {
current_node = current_node->next;
}
new_node = (Node *) malloc(sizeof(Node));
new_node->data = num;
new_node->next= current_node->next;
current_node->next = new_node;
return head;
}

/* Print all the elements in the linked list */
void print(Node *head) {
Node *current_node = head;
while ( current_node != NULL) {
printf(“%d “, current_node->data);
current_node = current_node->next;
}
}

/* Program main */
int main()
{
Node *head = NULL;
int num, prev_num, next_num;
int option;
char * temp;
char ch;
/* Display Menu */
while(1) {

printf(“\n ***********************************\n”);
printf(“\n * Linked list operations: *\n”);
printf(“\n * 1. Insert at the top of list *\n”);
printf(“\n * 2. Insert at bottom of list *\n”);
printf(“\n * 3. Insert after an element *\n”);
printf(“\n * 4. Insert before an element *\n”);
printf(“\n * 5. Show all elements *\n”);
printf(“\n * 6. Quit *\n”);
printf(“\n ***********************************\n”);
printf(“\n Choose an option [1-5] : “);
if (scanf(“%d”, &option) != 1) {
printf(” *Error: Invalid input. Try again.\n”);
scanf(“%s”, &temp); /*clear input buffer */
continue;
}

switch (option) {
case 1: /* Add to top*/
printf(” Enter a number to insert : “);
if (scanf(“%d”, &num) != 1) {
printf(” *Error: Invalid input.\n”);
scanf(“%s”, &temp); /*clear input buffer */
continue;
}
head = insert_top(num, head);
printf(“Number %d added to the top of the list”, num);
printf(“\nPress any key to continue…”);
getch();
break;

case 2: /* add to bottom */
printf(” Enter a number to insert : “);
if (scanf(“%d”, &num) != 1) {
printf(” *Error: Invalid input. \n”);
scanf(“%s”, &temp);
continue;
}
head = insert_bottom(num, head);
printf(“%d added to the bottom of the list”, num);
printf(“\nPress any key to continue…”);
getch();
break;

case 3: /* Insert After */
printf(” Enter a number to insert : “);
if (scanf(“%d”, &num) != 1) {
printf(” *Error: Invalid input.\n”);
scanf(“%s”, &temp);
continue;
}

printf(” After which number do you want to insert : “);
if (scanf(“%d”, &prev_num) != 1) {
printf(” *Error: Invalid input.\n”);
scanf(“%s”, &temp);
continue;
}
if (head != NULL) {
head = insert_after(num, prev_num, head);
printf(“%d is inserted after %d”, num, prev_num);
}else {
printf(“The list is empty”, num, prev_num);
}
printf(“\nPress any key to continue…”);
getch();
break;

case 4: /* Insert Before */
printf(” Enter a number to insert : “);
if (scanf(“%d”, &num) != 1) {
printf(” *Error: Invalid input. \n”);
scanf(“%s”, &temp);
continue;
}

printf(” Before which number do you want to insert : “);
if (scanf(“%d”, &prev_num) != 1) {
printf(” *Error: Invalid input.\n”);
scanf(“%s”, &temp);
continue;
}

if (head != NULL) {
head = insert_before(num, prev_num, head);
printf(“Number %d inserted before %d”, num, prev_num);
}else {
printf(“The list is empty”, num, prev_num);
}
printf(“\nPress any key to continue…”);
getch();
break;

case 5: /* Show all elements */
printf(“\nElements in the list: \n [ “);
print(head);
printf(“]\n\nPress any key to continue…”);
getch();
break;

case 6: /* Exit */
return(0);
break;

default:
printf(“Invalid Option. Please Try again.”);
getch();

} /* End of Switch */
} /* End of While */

return(0);
}