Data structures using C,
C program to illustrate the operations of singly linked list. Linked list is a data structure in which the objects are arranged in a linear order. Linked List contains group of nodes, in which each node contains two fields, one is data field and another one is the reference field which contains the address of next node. In this program we insert, delete, search, and display the linked list. Read more about C Programming Language .

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#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#include <string.h>
#define MAX 30

struct EMP
{
 int  empno;
 char empName[MAX];
 char designation[MAX];
 struct EMP *next;
};

/*********************************************************************/
/* Function to insert a node at the front of the linked list.        */
/* front: front pointer, id: employee ID, name: employee name        */
/* desg: Employee designation           */
/* Returns the new front pointer.                                    */
/*********************************************************************/

struct EMP* insert(struct EMP *front, int id, char name[], char desg[])
{
 struct EMP *newnode;

 newnode = (struct EMP*) malloc(sizeof(struct EMP));

 if (newnode == NULL)
 {
  printf("nAllocation failedn");
  exit(2);
 }
 newnode->empno = id;
 strcpy(newnode->empName, name);
 strcpy(newnode->designation, desg);
 newnode->next = front;
 front = newnode;
 return(front);
}                             /*End of insert() */

/* Function to display a node in a linked list */
void printNode(struct EMP *p)
{
 printf("nEmployee Details...n");
 printf("nEmp No    : %d", p->empno);
 printf("nName           : %s", p->empName);
 printf("nDesignation    : %sn", p->designation);
 printf("-------------------------------------n");
}                               /*End of printNode() */

/* ********************************************************/
/* Function to deleteNode a node based on employee number     */
/* front: front pointer, id: Key value                    */
/* Returns: the modified list.                            */
/* ********************************************************/

struct EMP* deleteNode(struct EMP *front, int id)
{
 struct EMP *ptr;
 struct EMP *bptr;    /* bptr is pointing to the node behind ptr */


 if (front->empno == id) 
 {
  ptr = front;
  printf("nNode deleted:");
  printNode(front);
  front = front->next;
  free(ptr);
  return(front);
 }

 for(ptr=front->next, bptr=front; ptr!=NULL; ptr=ptr->next, bptr=bptr->next)
 {
  if (ptr->empno == id)
  {
   printf("nNode deleted:");
   printNode(ptr);
   bptr->next = ptr->next;
   free(ptr);
   return(front);
  }
 }
 printf("nEmployee Number %d not found ", id);
 return(front);
}                              /*End of deleteNode() */

/*****************************************************************/
/* Function to search the nodes in a linear fashion based emp ID */
/* front: front pointer, key: key ID.                             */
/*****************************************************************/
void search(struct EMP *front, int key)
{
 struct EMP *ptr;

 for (ptr = front; ptr != NULL; ptr = ptr -> next)
 {
  if (ptr->empno == key)
  {
   printf("nKey found:");
   printNode(ptr);
   return;
  } 
 }
 printf("nEmployee Number %d not found ", key);
}                           /*End of search() */

/* Function to display the linked list */
void display(struct EMP *front)
{
 struct EMP *ptr;

 for (ptr = front; ptr != NULL; ptr = ptr->next)
 {
  printNode(ptr);
 }
}                         /*End of display() */

/* Function to display the menu of operations on a linked list */
void menu()
{
 printf("---------------------------------------------n");
 printf("Press 1 to INSERT a node into the list       n");
 printf("Press 2 to DELETE a node from the list       n");
 printf("Press 3 to DISPLAY the list                  n");
 printf("Press 4 to SEARCH the list                   n");
 printf("Press 5 to EXIT                              n");
 printf("---------------------------------------------n");
}                      /*End of menu() */

/* Function to select the option */
char option()
{
 char choice;

 printf("nn>> Enter your choice: ");
 switch(choice=getche())
 {
 case '1':
 case '2':
 case '3':
 case '4':
 case '5':   return(choice);
 default :    printf("nInvalid choice.");
 }
 return choice;
}            /*End of option() */

/* The main() program begins */
void main()
{
 struct EMP *linkList;
 char name[21], desig[51];
 char choice;
 int eno;

 linkList = NULL;

 printf("nWelcome to demonstration of singly linked listn");

 menu();       /*Function call */

 do {
  choice = option();          /*to choose oeration to be performed */

  switch(choice)
  {
  case '1': printf("nEnter the Employee Number      : ");
  scanf("%d", &eno);

  printf("Enter the Employee name        : ");
  fflush(stdin);
  gets(name);

  printf("Enter the Employee Designation : ");
  gets(desig);

  linkList = insert(linkList, eno, name, desig);
  break;

  case '2': printf("nnEnter the employee number to be deleted: ");
  scanf("%d", &eno);

  linkList = deleteNode(linkList, eno);
  break;

  case '3': if (linkList == NULL)
  {
   printf("nList empty.");
   break;
  }
  display(linkList);
  break;

  case '4': printf("nnEnter the employee number to be searched: ");
  scanf("%d", &eno);

  search(linkList, eno);
  break;

  case '5': break;
  }
 } while (choice != '5');
}             /*End fo main()*/

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