How to insert node at begin ,end and selected position in singly linked list?

Question

I am new for c programming ,i have tried myself inserting node in singly linked list program but i didn't get a proper output and i dont have any idea to correct my program if anybody knows please help.

#include<stdio.h>
#include<stdlib.h>
struct node
{
    int data;
    struct node *next;
}*head;
int loc;

void addbegin(int num)
{
    struct node *temp;
    temp=(struct node *)malloc(sizeof(struct node));
    temp->data=num;
    if(head=NULL)
    {
        head=temp;
        head->next=NULL;
    }
    else
    {
        temp->next=head;
        head=temp;
    }
}

void addend(int num)
{
    struct node *temp1,*temp2;
    temp1=(struct node *)malloc(sizeof(struct node));
    temp1->data=num;
    temp2=head;
    if(head==NULL)
    {
        head=temp1;
        head->next=NULL;
    }
    else
    {
        while(temp2->next != NULL)
        temp2=temp2->next;
        temp1->next=NULL;
        temp2->next=temp1;
    }

}

void pos(int num,int loc)
{
    int length();
    struct node *temp,*cur_ptr,*prev_ptr;

    int i;
    cur_ptr=head;
    if(loc > (length()+1) || loc<= 0)
    {
        printf("it is illegal call:");
    }
    else 
    {
        if(loc == 1)
        {
            addbegin(num);
        }
        else
        {
            for(i=1;i<loc;i++)
            {
                prev_ptr=cur_ptr;
                cur_ptr=cur_ptr->next;
            }
            temp=(struct node*)malloc(sizeof(struct node));
            temp->data=num;
            prev_ptr->next=temp;
            temp->next=cur_ptr;
        }
    }
}

int length()
{
    struct node *cur_ptr;
    int count = 0;
    cur_ptr=head;
    while(cur_ptr!=NULL)
    {
        cur_ptr=cur_ptr->next;
        count++;
    }
    return(count);
}
void display()
{
    struct node *temp=NULL;
    if(temp==NULL)
    {
        printf("list is empty:");
    }
    while(temp!=NULL)
    {
        printf("%d",temp->data);
        temp=temp->next;
    }
}

int main()
{

    int num;
    head=NULL;
    int choice;
    while(1)
    {
    printf("\nList Operations\n");
    printf("===============\n");
    printf("1.Insert at begin\n");
    printf("2.insert at end\n");
    printf("3.insert at selected position\n");
    printf("4.Display\n");
    printf("5.Exit\n");
    printf("Enter your choice : ");
    if(scanf("%d",&choice)<=0)
    {
        printf("Enter only an Integer\n");

    } 

    printf("enter your choice:");
    scanf("%d",&choice);
    switch(choice)
    {
    case 1: printf("Enter the number to insert at begin : ");
            scanf("%d",&num);
            addbegin(num);
            break;
    case 2: printf("Enter the number to insert at end: ");
            scanf("%d",&num);
            addend(num);
            break;
    case 3: printf("Enter the number to insert at selected position: ");
            scanf("%d",&num);
            pos(num,loc);
            break;
    case 4: printf("display the values");
            display();
            break;
    case 5: printf("exit");

    display();
    }
    }
    return 0;
}

i think the error is in my main function but am not clear in that please help

Answer 1

In your addbegin method there's at least one obvious error:

if(head=NULL)

should be

if (head == NULL)

as you need to compare, not assign.

In your pos method you have a function declaration: int length(); which shouldn't be there, but rather at the top, before main.

Another issue, this time in the display method:

void display()
{
    struct node *temp=NULL;
    if(temp==NULL) {
        printf("List is empty:");
    }
    while(temp!=NULL) {
        printf("%d",temp->data);
        temp=temp->next;
    }
}

Here temp will always be NULL, I guess you meant to assign head to the temp pointer, otherwise it will never traverse the list.

And finally, in the insert at specific position choice you need to ask for a location value and pass that along too the function call, so add a declaration for int loc; in main, and change the third case to this:

case 3:
            printf("Enter the number to insert at selected position: ");
            scanf("%d",&num);
            printf("Enter the position: ");
            scanf("%d",&loc);
            pos(num,loc);
            break;

to the

Finally I'm going to quote from the C99 standard, section 5.1.2.2.1 Program startup :

The function called at program startup is named main. The implementation declares no prototype for this function. It shall be defined with a return type of int and with no parameters:

int main(void) { /* ... */ }

or with two parameters (referred to here as argc and argv, though any names may be used, as they are local to the function in which they are declared):

int main(int argc, char *argv[]) { /* ... */ }

So, please, change your declaration of main and include a return line at the end (possibly return 0; indicating successful program exit).

This became rather lengthy. After the suggested changes your program should look something like this:

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

struct node {
    int data;
    struct node *next;
}*head;

void addbegin(int num)
{
    struct node *temp;
    temp = malloc(sizeof(struct node));
    temp->data=num;
    if(head==NULL) {
        head=temp;
        head->next=NULL;
    } else {
        temp->next=head;
        head=temp;
    }
}

void addend(int num)
{
    struct node *temp1, *temp2;
    temp1 = malloc(sizeof(struct node));
    temp1->data = num;
    temp2 = head;
    if(head == NULL) {
        head = temp1;
        head->next = NULL;
    } else {
        while(temp2->next != NULL)
            temp2=temp2->next;
        temp1->next=NULL;
        temp2->next=temp1;
    }
}

int length()
{
    struct node *cur_ptr;
    int count = 0;
    cur_ptr = head;
    while(cur_ptr != NULL) {
        cur_ptr = cur_ptr->next;
        count++;
    }
    return (count);
}

void pos(int num, int loc)
{
    struct node *temp, *cur_ptr, *prev_ptr;

    int i;
    cur_ptr=head;
    if(loc > (length()+1) || loc<= 0) {
        printf("it is illegal call:");
    } else {
        if(loc == 1) {
            addbegin(num);
        } else {
            for(i=1; i<loc; i++) {
                prev_ptr=cur_ptr;
                cur_ptr=cur_ptr->next;
            }
            temp = malloc(sizeof(struct node));
            temp->data=num;
            prev_ptr->next=temp;
            temp->next=cur_ptr;
        }
    }
}

void display()
{
    struct node *temp = head;
    if(temp == NULL) {
        printf("List is empty:");
    }

    printf("The list contains the following values:\n");
    while(temp!=NULL) {
        printf("%d\n",temp->data);
        temp=temp->next;
    }
}

int main()
{
    int choice, num, loc;
    head = NULL;

    while(1) {
        printf("\nList Operations\n");
        printf("===============\n");
        printf("1.Insert at begin\n");
        printf("2.insert at end\n");
        printf("3.Insert at selected position\n");
        printf("4.Display\n");
        printf("5.Exit\n");
        printf("Enter your choice : ");
        if(scanf("%d",&choice)<=0) {
            printf("Enter only an Integer\n");
        }

        switch(choice) {
        case 1:
            printf("Enter the number to insert at begin : ");
            scanf("%d",&num);
            addbegin(num);
            break;
        case 2:
            printf("Enter the number to insert at end: ");
            scanf("%d",&num);
            addend(num);
            break;
        case 3:
            printf("Enter the number to insert at selected position: ");
            scanf("%d",&num);
            printf("Enter the position: ");
            scanf("%d",&loc);
            pos(num,loc);
            break;
        case 4:
            printf("Display the values\n");
            display();
            break;
        case 5:
            printf("exit");
            exit(0); // maybe you should exit here.
            display();
        }
    }

    return 0;
}

Answer 2

void addbegin(int num)
{
struct node *temp;
temp=(struct node *)malloc(sizeof(struct node));
temp->data=num;
  if(head==NULL)
  {
    head=temp;
    head->next=NULL;
  }
  else
  {
    temp->next=head;
    head=temp;
  }
}

and

void display()
{
struct node *temp=NULL;
temp = head;
  if(temp==NULL)
  {
    printf("list is empty:");
  }
  while(temp!=NULL)
  {
    printf("%d",temp->data);
    temp=temp->next;
  }
}

Answer 3

#include<stdio.h>
#include<stdlib.h>
struct node
{
    int data;
    struct node *next;
}*head;

int loc;

void addbegin(int num)
{
    struct node *temp;
    temp=(struct node *)malloc(sizeof(struct node));
    temp->data=num;
    if(head==NULL) //this not assign, you need == to compare
    {
        head=temp;
        head->next=NULL;
    }
    else
    {
        temp->next=head;
        head=temp;
    }
}

void addend(int num)
{
    struct node *temp1,*temp2;
    temp1=(struct node *)malloc(sizeof(struct node));
    temp1->data=num;
    temp2=head;
    if(head==NULL)
    {
        head=temp1;
        head->next=NULL;
    }
    else
    {
        while(temp2->next != NULL)
            temp2=temp2->next;
        temp1->next=NULL;
        temp2->next=temp1;
    }

}

int length()
{
    struct node *cur_ptr;
    int count = 0;
    cur_ptr=head;
    while(cur_ptr!=NULL)
    {
        cur_ptr=cur_ptr->next;
        count++;
    }
    return(count);
}

void pos(int num,int loc)
{
    struct node *temp,*cur_ptr,*prev_ptr;

    int i;
    cur_ptr=head;
    if(loc > (length()+1) || loc<= 0)
    {
        printf("it is illegal call:");
    }
    else 
    {
        if(loc == 1)
        {
            addbegin(num);
        }
        else
        {
            for(i=1;i<loc;i++)
            {
                prev_ptr=cur_ptr;
                cur_ptr=cur_ptr->next;
            }
            temp=(struct node*)malloc(sizeof(struct node));
            temp->data=num;
            prev_ptr->next=temp;
            temp->next=cur_ptr;
        }
    }
}


void display()
{
    struct node *temp=head;
    if(temp==NULL)
    {
        printf("list is empty:");
    }
    while(temp!=NULL)
    {
        printf("%d ",temp->data);
        temp=temp->next;
    }
    printf("\n");
}

int main()
{

    int num;

    int choice;
    while(1)
    {
        printf("\nList Operations\n");
        printf("===============\n");
        printf("1.Insert at begin\n");
        printf("2.insert at end\n");
        printf("3.insert at selected position\n");
        printf("4.Display\n");
        printf("5.Exit\n");
        printf("Enter your choice : ");
        if(scanf("%d",&choice)<=0)
        {
            printf("Enter only an Integer\n");

        } 

        switch(choice)
        {
        case 1: printf("Enter the number to insert at begin : ");
            scanf("%d",&num);
            addbegin(num);
            break;
        case 2: printf("Enter the number to insert at end: ");
            scanf("%d",&num);
            addend(num);
            break;
        case 3: printf("Enter the number to insert at selected position: ");
            scanf("%d",&num);
            pos(num,loc);
            break;
        case 4: printf("\ndisplay the values: ");
            display();
            break;
        case 5: printf("exit");
            display();
        }
    }
    return 0;
}

Answer 4

Try this

#include<stdio.h>
#include<stdlib.h>
struct node
{
    int data;
    struct node *next;
}*head;

int loc;

void addbegin(int num)
{
    struct node *temp;
    temp=(struct node *)malloc(sizeof(struct node));
    temp->data=num;
    if(head==NULL) //this not assign, you need == to compare
    {
        head=temp;
        head->next=NULL;
    }
    else
    {
        temp->next=head;
        head=temp;
    }
}

void addend(int num)
{
    struct node *temp1,*temp2;
    temp1=(struct node *)malloc(sizeof(struct node));
    temp1->data=num;
    temp2=head;
    if(head==NULL)
    {
        head=temp1;
        head->next=NULL;
    }
    else
    {
        while(temp2->next != NULL)
            temp2=temp2->next;
        temp1->next=NULL;
        temp2->next=temp1;
    }

}

int length()
{
    struct node *cur_ptr;
    int count = 0;
    cur_ptr=head;
    while(cur_ptr!=NULL)
    {
        cur_ptr=cur_ptr->next;
        count++;
    }
    return(count);
}

void pos(int num,int loc)
{
    struct node *temp,*cur_ptr,*prev_ptr;

    int i;
    cur_ptr=head;
    if(loc > (length()+1) || loc<= 0)
    {
        printf("it is illegal call:");
    }
    else 
    {
        if(loc == 1)
        {
            addbegin(num);
        }
        else
        {
            for(i=1;i<loc;i++)
            {
                prev_ptr=cur_ptr;
                cur_ptr=cur_ptr->next;
            }
            temp=(struct node*)malloc(sizeof(struct node));
            temp->data=num;
            prev_ptr->next=temp;
            temp->next=cur_ptr;
        }
    }
}


void display()
{
    struct node *temp=head;
    if(temp==NULL)
    {
        printf("list is empty:");
    }
    while(temp!=NULL)
    {
        printf("%d ",temp->data);
        temp=temp->next;
    }
    printf("\n");
}

int main()
{

    int num;

    int choice;
    while(1)
    {
        printf("\nList Operations\n");
        printf("===============\n");
        printf("1.Insert at begin\n");
        printf("2.insert at end\n");
        printf("3.insert at selected position\n");
        printf("4.Display\n");
        printf("5.Exit\n");
        printf("Enter your choice : ");
        if(scanf("%d",&choice)<=0)
        {
            printf("Enter only an Integer\n");

        } 

        switch(choice)
        {
        case 1: printf("Enter the number to insert at begin : ");
            scanf("%d",&num);
            addbegin(num);
            break;
        case 2: printf("Enter the number to insert at end: ");
            scanf("%d",&num);
            addend(num);
            break;
        case 3: printf("Enter the number to insert at selected position: ");
            scanf("%d",&num);
            printf("Enter the position to insert: 1 for insert at begin, so on: ");
            scanf("%d",&loc);
            pos(num,loc);
            break;
        case 4: printf("\ndisplay the values: ");
            display();
            break;
        case 5: 
            display();
        printf("\n exiting program \n");
        exit(0);
        }
    }
    return 0;
}