Implementing linked list in C

Question

I am trying to implement linked list in C, having options for creation, insertion, deletion and display. My code is:

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

void createFirst(int);
void appendNode(int);
void insertFirst(int);
void insertNode(int,int);
void deleteFirst();
void deleteNode(int);
void display();

struct Node
{
    int data;
    struct Node *link;
};

typedef struct Node Node;

Node *start = NULL;
int count=0;

void main()
{
    int ch;
    do
    {
        printf("\f\n");
        printf("1. Create the list \n");
        printf("2. Insert an element at any position \n");
        printf("3. Delete an element at any position \n");
        printf("4. Display the list \n");
        printf("5. Quit \n");
        printf("Enter your choice : \n");
        scanf("%d",&ch);
        switch(ch)
        {
            case 1:
            {
                int a;
                char c;
                printf("Enter the data : \n");
                scanf("%d",&a);
                createFirst(a);
                while(1)
                {
                    printf("Do you want to continue[Y/N] : \n");
                    scanf("  %c",&c);
                    if(c=='Y' || c=='y')
                    {
                        printf("Enter the data : \n");
                        scanf("%d",&a);
                        appendNode(a);
                    }
                    else if(c=='N' || c=='n')
                    {
                        break;
                    }
                    else
                    {
                        continue;
                    }
                }
                break;
            }
            case 2:
            {
                int a,pos;
                char c;
                printf("Enter the data : \n");
                scanf("%d",&a);
                printf("Enter the position : \n");
                scanf("%d",&pos);
                if(pos == 1)
                {
                    insertFirst(a);
                }
                else
                {
                    insertNode(pos,a);
                }
                while(1)
                {
                    printf("Do you want to continue[Y/N] : ");
                    scanf(" %c",&c);
                    if(c=='N' || c=='n')
                    {
                        break;
                    }
                    if(c!='Y' && c!='y')
                    {
                        continue;
                    }
                    printf("Enter the data : \n");
                    scanf("%d",&a);
                    printf("Enter the position : \n");
                    scanf("%d",&pos);
                    if(pos == 1)
                    {
                        insertFirst(a);
                    }
                    else
                    {
                        insertNode(pos,a);
                    }
                }
                break;
            }
            case 3:
            {
                int pos;
                char c;
                printf("Enter the position : \n");
                scanf("%d",&pos);
                if(pos == 1)
                {
                    deleteFirst();
                }
                else
                {
                    deleteNode(pos);
                }
                while(1)
                {
                    printf("Do you want to continue[Y/N] : ");
                    scanf(" %c",&c);
                    if(c=='N' || c=='n')
                    {
                        break;
                    }
                    if(c!='Y' && c!='y')
                    {
                        continue;
                    }
                    printf("Enter the position : \n");
                    scanf("%d",&pos);
                    if(pos == 1)
                    {
                        deleteFirst();
                    }
                    else
                    {
                        deleteNode(pos);
                    }
                }
                break;
            }
            case 4:
            {
                display();
                break;
            }
            case 5:
            {
                return;
            }
            default:
            {
                printf("Invalid choice \n");
                break;
            }
        }
    }while(ch!=5);
}

void createFirst(int d)
{
    Node newnode = {d,NULL};
    start = &newnode;
    count++;
}

void appendNode(int d)
{
    Node temp = *start;
    while(temp.link != NULL)
    {
        temp = *temp.link;
    }
    Node newnode = {d,NULL};
    temp.link = &newnode;
    count++;
}

void insertFirst(int d)
{
    Node newnode = {d,NULL};
    newnode.link = start;
    start = &newnode;
    count++;
}

void insertNode(int n,int d)
{
    if(n>count || n<count)
    {
        printf("Invalid position \n");
        return;
    }
    Node temp = *start;
    int i;
    for(i=1;i<n-1;i++)
    {
        temp = *temp.link;
    }
    Node newnode = {d,NULL};
    newnode.link = temp.link;
    temp.link = &newnode;
}

void deleteFirst()
{
    if(start != NULL)
    {
        printf("Deleted element : %d \n",(*start).data);
        start = (*start).link;
        count--;
    }
    else
    {
        printf("Underflow \n");
    }
}

void deleteNode(int n)
{
    if(n>count || n<count)
    {
        printf("Invalid position \n");
        return;
    }
    Node temp = *start;
    int i;
    for(i=1;i<n-1;i++)
    {
        temp = *temp.link;
    }
    printf("Deleted node : %d",temp.link->data);
    temp = *(temp.link->link);
    count--;
}

void display()
{
    if(start == NULL)
    {
        printf("The list is empty \n");
        return;
    }
    Node temp = *start;
    int i;
    for(i=1;i<=count;i++)
    {
        printf("%d ",temp.data);
        temp = *temp.link;
    }
}

But:

Whenever the control is going to appendNode function, the program terminates somehow.
After only creating the first node, if i go to display, it is printing some garbage value.

Please somebody help.

first problem, your createFirst function creates a node in automatic memory which dies as soon as createFirst exits, meaning that start points to nothing after that. You need to malloc memory for the node in order for it to persist after the function call. It looks like this is a common problem throughout your code. — yano
– yano, Commented Nov 11, 2021 at 5:27
This is tagged C++, but the concept of what you're doing is exactly the same: stackoverflow.com/questions/6441218/… — yano
– yano, Commented Nov 11, 2021 at 5:30

ADBeveridge · Accepted Answer · 2021-11-11 05:30:25Z

1

Your problem is on the line (inside of appendNode) which contains this: Node temp = *start;. Don't do it that way. Do it this way:

Node *temp = start;

Change the following pointer notations to accomodate this change. Like change the dot operators to the -> operator. Here's the rest of the function:

while(temp->link != NULL)
{
    temp = temp->link;
}
Node *newnode = malloc (sizeof(struct Node));
newnode->data = 0;
newnode->link = NULL;

temp->link = newnode;
count++;

edited Nov 11, 2021 at 5:30

answered Nov 11, 2021 at 5:26

ADBeveridge

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4 Comments

SuperStormer Over a year ago

Would you mind providing an explanation of your answer?

Surya Majumder Over a year ago

Ok thanks @ADBeveridge I will try.

Surya Majumder Over a year ago

Thank you thanks a lot @ADBeveridge . It really helped.

Surya Majumder Over a year ago

Thank you thanks a lot @yano. It really helped.

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