Question

Hi,

I am working on an assignment in C-Programming language dealing with LInked lists,

in the code there is instructions on where to write the code. I do not know how to write Linked Lists.

Has to be in the C-language, Any help is greatly appreciated  

//agelink.c
//maintains list of agents
//uses linked list

#include <stdio.h>
#include <stdlib.h>
#define TRUE 1

void listall(void);
void newname(void);
void delink(void);
void memexit(void);
void wfile(void);

/*********************************************************************
this is the structure to hold a agent information.
prt *ptrnext is a point to link to next prt structure

*********************************************************************/
struct prs
{
   char name[40];
   int agnumb;
   float height;  
   struct prs *ptrnext;
};

struct prs *ptrfirst = NULL;
int n = 0;

/***********************************************************************
main() calls other methods depending on user choice. you do not need the change code here.
**********************************************************************/
void main(void){
  
   while(TRUE) // cycle until user chooses 'q'
   {
       printf("\n'e' enter new agent\n'l' list all agents");
       printf("\n 'd' delete a agent\n'r' read file\n'q' exit: ");
       char option;
       scanf("%c", &option);
       switch(option) //gethche() gets()
       {
           case 'e': newname(); break;
           case 'l': listall(); break;
           case 'd': delink(); break;
           case 'q': memexit(); break;
           default:
               printf("\nEnter only selections listed"); //puts("this is to be print out to screen")
                      
       }//end switch
                  
   }//end while  
  
}// end main();

/**************************************************************
Complete this methods to ask user to enter agent name,
agent number, and agent height to add a new agent to the
linked list.
use scanf() to read from the user inputs
use atoi to convert char to integers.
**************************************************************/
void newname(void){
  
   struct prs *ptrthis; // this is the pointer to new agent.
  
   char numstr[81];
  
   ptrthis = malloc(sizeof(struct prs));
   if(ptrthis==NULL)
   {
       printf("\nCan't reallocate memory");
       return;
   }
   //your code start here

   if(!ptrfirst)
   ptrfirst = ptrthis;
   else
   {
       ptrfirst->ptrnext = ptrthis; // note: you need make the line right to handle additonal link.
   }
  
  
  
}
/**************************************************************
Complete this method to print out all the agent list to screen
**************************************************************/
void listall(void){
  
   struct prs *ptrthis;
  
  
   if(ptrfirst == NULL){
       printf("\nEmpty list");
       perror("error in listall method");
       return ;
   }
  
   ptrthis = ptrfirst;
   // in this do while loop, to print out the list
   do{
  
   }
   while (ptrthis != NULL);

  
  
}
/******************************************************************
//delink()
//delete entry in agent list matching the name from user input

******************************************************************/
void delink(void){
  
   struct prs *ptrthis, *ptrlast; // utility pointer
   char delname[81];
  
   if(ptrfirst == NULL){
       printf("\nEmpty list in delink.\n");
       return;
   }
  
   printf("\nEnter name ot be deleted: ");
  
   scanf("%s",&delname);
  
   ptrthis = ptrfirst;
  
   //implement logica here to search and delete the record matching the name
   // user input from terminal. do not forget to free the memory resouces
   //used by the deleted records using free(void *ptr) method.
  
   do{
      

      
   }while(ptrthis !=NULL);
  
   printf("No such name on list\n");

  
  
}

//fee all memeory and exist;

void memexit(void){

   struct prs *ptrthis, *ptrfree;

   if(ptrfirst == NULL)
       exit(0);
  
   ptrthis = ptrfirst;
   do{
      
       ptrfree = ptrthis;
       ptrthis = ptrthis->ptrnext;
       free(ptrfree);
   }while (ptrthis != NULL);
  
   exit(0);

}

Answer 1

Code: agelink.c

//agelink.c
//maintains list of agents
//uses linked list

#include <stdio.h>
#include <stdlib.h>
#include <string.h> //strcmp
#define TRUE 1

void listall(void);
void newname(void);
void delink(void);
void memexit(void);
void wfile(void);

/*********************************************************************
this is the structure to hold a agent information.
prt *ptrnext is a point to link to next prt structure

*********************************************************************/
struct prs
{
   char name[40];
   int agnumb;
   float height;  
   struct prs *ptrnext;
};

struct prs *ptrfirst = NULL;
int n = 0;

/***********************************************************************
main() calls other methods depending on user choice. you do not need the change code here.
**********************************************************************/
void main(void){
  
   while(TRUE) // cycle until user chooses 'q'
   {
       printf("\n'e' enter new agent\n'l' list all agents");
       printf("\n 'd' delete a agent\n'r' read file\n'q' exit: ");
       char option;
       scanf("%c", &option);
       getchar();
       switch(option) //gethche() gets()
       {
           case 'e': newname(); break;
           case 'l': listall(); break;
           case 'd': delink(); break;
           case 'q': memexit(); break;
           default:
               printf("\nEnter only selections listed"); //puts("this is to be print out to screen")
                      
       }//end switch
                  
   }//end while  
  
}// end main();

/**************************************************************
Complete this methods to ask user to enter agent name,
agent number, and agent height to add a new agent to the
linked list.
use scanf() to read from the user inputs
use atoi to convert char to integers.
**************************************************************/
void newname(void){
  
   struct prs *ptrthis; // this is the pointer to new agent.
  
   char numstr[81];
  
   ptrthis = malloc(sizeof(struct prs));
   if(ptrthis==NULL)
   {
       printf("\nCan't reallocate memory");
       return;
   }
   //your code start here
        printf("Enter Agent's name:");
        scanf("%s", &(ptrthis->name));
        getchar();
        printf("Enter Agent' age: ");
        scanf("%d", &(ptrthis->agnumb));
        getchar();
        printf("Enter Agent's height: ");
        scanf("%f", &(ptrthis->height));
        getchar();
        ptrthis->ptrnext = NULL;
        
   if(!ptrfirst)
   ptrfirst = ptrthis;
   else
   {
        ptrthis->ptrnext = ptrfirst; // note: you need make the line right to handle additonal link.
        ptrfirst = ptrthis;
   }
}
/**************************************************************
Complete this method to print out all the agent list to screen
**************************************************************/
void listall(void){
  
   struct prs *ptrthis;
  
  
   if(ptrfirst == NULL){
       printf("\nEmpty list");
       perror("error in listall method");
       return ;
   }
  
   ptrthis = ptrfirst;
   // in this do while loop, to print out the list
   do{
                printf("\n");
                printf("Name: %s\n", ptrthis->name);
                printf("Age: %d\n", ptrthis->agnumb);
                printf("Height: %f\n", ptrthis->height);
                ptrthis = ptrthis->ptrnext;
   }
   while (ptrthis != NULL);
  
}
/******************************************************************
//delink()
//delete entry in agent list matching the name from user input

******************************************************************/
void delink(void){
  
   struct prs *ptrthis, *ptrlast; // utility pointer
   char delname[81];
   int flag = TRUE; //flag to indicate successful search
  
   if(ptrfirst == NULL){
       printf("\nEmpty list in delink.\n");
       return;
   }
  
   printf("\nEnter name ot be deleted: ");
  
   scanf("%s",&delname);
  getchar();
   ptrthis = ptrfirst;
        
   //implement logica here to search and delete the record matching the name
   // user input from terminal. do not forget to free the memory resouces
   //used by the deleted records using free(void *ptr) method.
  ptrlast = ptrfirst;
   do{
                //compare the name on the list
      if(strcmp(ptrthis->name, delname)==0){
        //handle if first node is being deleted
        if(ptrthis == ptrfirst){
                ptrfirst = ptrfirst->ptrnext;
                  }
        ptrlast->ptrnext = ptrthis->ptrnext;
        free(ptrthis);
        ptrthis = NULL;
        flag = TRUE-1;
        //break the while loop here
        break;
          }
                ptrlast = ptrthis;
                ptrthis = ptrthis->ptrnext;
      
   }while(ptrthis !=NULL);
  
   if(flag==TRUE)
        printf("No such name on list\n");
        else
                printf("Agent with name '%s' has been deleted\n", delname);

}

//free all memeory and exist;

void memexit(void){

   struct prs *ptrthis, *ptrfree;

   if(ptrfirst == NULL)
       exit(0);
  
   ptrthis = ptrfirst;
   do{
      
       ptrfree = ptrthis;
       ptrthis = ptrthis->ptrnext;
       free(ptrfree);
   }while (ptrthis != NULL);
        ptrfirst = NULL; //make list empty
   exit(0);

}

Output:

Note: Please try to avoid using do-while loop. Instead, use while or for loop. Using do-while loop is not the best practice as it does the task before validating the loop condition.