Thread: Help??How to solve this error??

In line 58,60,62 you provide pointer to char while scanf expects pointer to int. It will result in memory overruns (scanf will write 4 bytes where only 1 is available)

In line 67 and further you are using data as if it is struct, but it is declared as pointer. (it is not initialized pointer - so you cannot write anything till you initialize it.)

I suggest you start writing smaller parts of your program - compile them and test, make sure that they are working correctly before you continue adding more code to your program

Thanks to anduril462, I can now compile and run my code very well for the Insert_First method of the linkedlist.Now then, if I want to check if the CarData data object is NULL for my insert_specific method,how can I do it for the code below as the while loop requires this condition.

Code:

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


#define MAX_WORD_LENGTH 10


typedef struct cardata{
    
    char carname[MAX_WORD_LENGTH];
    char carmodel[MAX_WORD_LENGTH];
    char caryear[MAX_WORD_LENGTH];
    
}CarData;


struct node{
    
    CarData data;
    struct node *next;
    struct node *prev;
}*start=NULL;




void insert_first(){
    struct node *ptr;
    char carname[MAX_WORD_LENGTH];
    char carmodel[MAX_WORD_LENGTH];
    char caryear[MAX_WORD_LENGTH];
    
    printf("\n\nEnter the car name: ");
    scanf("%s", carname);
    printf("\n\nEnter the car model: ");
    scanf("%s", carmodel);
    printf("\n\nEnter the car year: ");
    scanf("%s", caryear);
    
    if(start==NULL){
        
        start=(struct node *)malloc(sizeof(struct node));
        strcpy(start->data.carname,carname);
        strcpy(start->data.carmodel,carmodel);
        strcpy(start->data.caryear,caryear);
        start->prev=NULL;
        start->next=NULL;
        
    }else{
        
        ptr=start;
        start=(struct node *)malloc(sizeof(struct node));
        strcpy(start->data.carname,carname);
        strcpy(start->data.carmodel,carmodel);
        strcpy(start->data.caryear,caryear);
        start->next=ptr;
        
    }
    
}


void insert_specific()
{
    int n, item;
    struct node *new , *ptr;
    char carname[MAX_WORD_LENGTH];
    char carmodel[MAX_WORD_LENGTH];
    char caryear[MAX_WORD_LENGTH];
    /*If the linked list is empty*/
    if(start == NULL){
        printf("\n\nLinked list is empty. It must have at least one node. \n");
        
    }else{
    
        /*If the linked list is empty*/
        printf("\n\nEnter INFO after which new node is to be inserted: ");
        scanf("%d", &n);
        printf("\n\nEnter ITEM: ");
        scanf("%d", &item);
        
        /*The node pointed by the start will be pointed by the pointer ptr*/
        ptr = start;
        
        /*If pointer is not dangling pointer*/
        while(ptr != NULL){
            
            /*If the  value of  member variable info pointed by ptr is  0 */
            if(ptr->data==NULL)
            {
                /*Allocate the memory for the variable of type node that will be pointed by new pointer*/
                new = (struct node *)malloc(sizeof(struct node));
                
                /*Item will be stored into the member variable info in new node */
                strcpy(new->data.carname,carname);
                strcpy(new->data.carmodel,carmodel);
                strcpy(new->data.caryear,caryear);
                
                /*The address that was pointed by pt->link will also be now pointed by  new */
                new->next = ptr->next;
                
                /*Pointer ptr will now point to address of new node*/
                ptr->next= new;
                
                printf("\n\nItem inserted: %d", item);
                return;
            }else{
                ptr= ptr->next;
            }
        }
    }
}


void display()
{
    struct node *ptr=start;
    int i=1;
    
    if(ptr == NULL){
        printf("\nLinklist is empty.\n");
    }else{
        printf("\nSr. No  Address    Make     Model     Year    Previous      Next\n");
        while(ptr != NULL){
            printf("\n%d.\t%d    %s    %s      %s  %d\t     %d\n", i, ptr, ptr->data.carname,ptr->data.carmodel,ptr->data.caryear,ptr->prev,ptr->next);
            ptr = ptr->next;
            i++;
        }
    }
}


int main(void)
{
    int ch;
    do 
    {
        printf("\n\n\n1. Insert First\n2. Display\n3. Exit\n");
        printf("\nEnter your choice: ");
        scanf("%d", &ch);
        
        switch(ch)
        {
            
            case 1:
                insert_first();
                break;
            case 2:
                insert_specific();
                break;    
            case 3:
                display();
                break;
            case 4:
                exit(0);
            default:
                printf("\n\nInvalid choice. Please try again. \n");
                
        }
        
    } while(1);
    
    return EXIT_SUCCESS;
}

Originally Posted by i++

Thanks to anduril462, I can now compile and run my code very well for the Insert_First method of the linkedlist.Now then, if I want to check if the CarData data object is NULL for my insert_specific method,

You just do not have such nodes in your list.
Each node that is inserted - has a filled Data member.

I have noted in your code in lines 40-58 - you failed to initialize prev in the else case for new node and for the prev node as well.

I feel you better join both cases in something generic like

Code:

        ptr=start; /* could be NULL */
        start=(struct node *)malloc(sizeof(struct node));
        strcpy(start->data.carname,carname);
        strcpy(start->data.carmodel,carmodel);
        strcpy(start->data.caryear,caryear);
        start->next=ptr;
        start->prev=NULL; /* was missing */

        if(ptr != NULL) /* need to initialize prev - due to line above it is still NULL */
        {
            ptr->prev = start;
        }

And as addition to the previous post line 2 in it I would change to

Code:

start=malloc(sizeof(*start));

I think the reasons you can find in FAQ if desired

I do not like that you bumped your thread. People will see it, whether you do it or not. Moreover, imagine how the number of posts in every thread would increase, without a reason, if everybody did that.

Your problem is here:

Code:

struct node{
     
    CarData data;
    struct node *next;
    struct node *prev;
}*start=NULL;                     <---- HERE

You need to write stuct node *.
If you want to set your pointer to NULL, I suggest doing that inside main, or inside a function.
If you want to typedef (I would not recommend it now), you need to write

Code:

typedef stuct node * start;

I feel you need an example to structs. Here you are.

Thanks whiteflags, I already fixed that solution.Now then,in my program,I plan to filter choices for the users to get a specific piece of data for the inventory. For instance,at start of the program, there will be menu that gives user option to add or delete data and then for instance if they say insert then I will give them option to select a car company(i.e. like Toyota or Honda) and once they select that company I will give them choice of all Toyota models they can add in the inventory.This will happen so I can narrow down and do a selected operation on the information I have been given.


The thing is I don't know how to filter out the models for a specific company.I have created different arrays containing different models but I don't know how to display user option of models for that company.


Here is my code..

Code:

    #include <stdio.h>
    #include <stdlib.h>
    
    #define MAX_WORD_LENGTH 20
    
    #define MAX_SIZE 100
    typedef struct cardata{
        
        char carname[MAX_WORD_LENGTH];
        char carmodel[MAX_WORD_LENGTH];
        char caryear[MAX_WORD_LENGTH];
        char cartype[MAX_WORD_LENGTH];
        int  quantity;
        
    }CarData;
    
    
    struct node{
        
        CarData data;
        struct node *next;
        struct node *prev;
    }*start=NULL;
    
    const char *companyList[10] = {"Toyota", "Honda","Hyundai","Nissan","Mitsubishi","VoksWagon","Acura","Ford","Dodge","GMC"};
    const char *companyModels[10] = {toyotaModels,hondamodels,hyundaimodels,nissanmodels,mitsubishimodels,vokswagonmodels,acuramodels,fordmodels,dodgemodels,gmcmodels};
    const char *toyotaModels[10]={"Corolla","Camery"}
    const char *hondaModels[10]={"Civic","Accord"};
    
    
    void insert_first(){
        struct node *ptr;
        
        char carname[MAX_WORD_LENGTH];
        char carmodel[MAX_WORD_LENGTH];
        char caryear[MAX_WORD_LENGTH];
        char cartype[MAX_WORD_LENGTH];
        int  carQuantity;
        int ch;
        
        printf("\n\n\n1.Toyota \n2.Honda \n3.Hyundai \n4.Nissan \n5.Mitsubishi \n6.Volksvagon \n7.Acura \n8.Ford \n9.Dodge \n10.GMC\n");
        printf("\nPress a number to select corresponding car(i.e. 1 for toyota, 2 for honda): ");
        scanf("%d", &ch);
        strcpy(carname,companyList[ch-1]);
        printf("\n\nEnter the car model: ");
        scanf("%s", carmodel);
        printf("\n\nEnter the car year: ");
        scanf("%s", caryear);
        printf("\n\nEnter the car type: ");
        scanf("%s", cartype);
        printf("\n\nEnter the  quantity of models: ");
        scanf("%d", &carQuantity);
    
        
        if(start==NULL){
            
            start=(struct node *)malloc(sizeof(struct node));
            strcpy(start->data.carname,carname);
            strcpy(start->data.carmodel,carmodel);
            strcpy(start->data.caryear,caryear);
            strcpy(start->data.cartype,cartype);
            start->data.quantity=carQuantity;
            start->prev=NULL;
            start->next=NULL;
            
        }else{
            
            ptr=start;
            start=(struct node *)malloc(sizeof(struct node));
            strcpy(start->data.carname,carname);
            strcpy(start->data.carmodel,carmodel);
            strcpy(start->data.caryear,caryear);
            strcpy(start->data.cartype,cartype);
            start->data.quantity=carQuantity;
            start->next=ptr;
            
        }
        
    }
    
    void delete_first(){
        
        struct node *ptr;
        char carname[MAX_WORD_LENGTH];
        char carmodel[MAX_WORD_LENGTH];
        char caryear[MAX_WORD_LENGTH];
        char cartype[MAX_WORD_LENGTH];
        char modelNumber[MAX_WORD_LENGTH];
        int  carQuantity;
        
        if(start==NULL){
            printf("\n\nLinked list is empty.\n");
        }else{
            ptr=start;
            printf("\nThe car for which the entry is removed is %s \n",ptr->data.carname);
            strcpy(start->data.carname,carname);
            strcpy(start->data.carmodel,carmodel);
            strcpy(start->data.caryear,caryear);
            strcpy(start->data.cartype,cartype);
            start->data.quantity=carQuantity;
            start=start->next;
            free(ptr);
        }
    }
    
    void display()
    {
        struct node *ptr=start;
        int i=1;
        
        if(ptr == NULL){
            printf("\nLinklist is empty.\n");
        }else{
            printf("\nSr. No   Make     Model    Year   Type  Quantity\n");
            while(ptr != NULL){
                printf("\n%d.\t%s   %s   %s   %s   %d\n", i,ptr->data.carname,ptr->data.carmodel,ptr->data.caryear,ptr->data.cartype,ptr->data.quantity);
                ptr = ptr->next;
                i++;
            }
            
        }
    }
    
    int main(void)
    {
        int ch;
        do 
        {
            printf("\n\n\n1. Insert \n2. Delete \n3. Display \n4. Exit\n");
            printf("\nEnter your choice: ");
            scanf("%d", &ch);
            
            switch(ch)
            {
                
                case 1:
                    insert_first();
                    break;
                case 2:
                    delete_first();
                    break;    
                case 3:
                    display();
                    break;
                case 4:
                    exit(0);                                            
                default:
                    printf("\n\nInvalid choice. Please try again. \n");
                    
            }
            
        } while(1);
        
        
        return 0;
    }

If it were me I would prepare a smaller array based on the user's choice. To further explain, I would depend a master array of all the CarData from the cars that a user can purchase. From that array, create a smaller array of all the cars that match the make.

This array can be composed in a loop. I will give you the general idea in pseudocode, but you will have to write it in C.

Code:

for each car in inventory:
  if strcmp(car.make, userMake) == 0:
    copy car to filtered array

It's not the fanciest way, but it works. Once you have that array you can pare it down even further with the user's other specifications by using similar techniques. Or just print out the filtered array with printf().