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

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



void append(int num)
{
    struct node *temp,*right;
    temp= (struct node *)malloc(sizeof(struct node));
    temp->data=num;
    right=(struct node *)head;
    while(right->next != NULL)
    right=right->next;
    right->next =temp;
    right=temp;
    right->next=NULL;
}



void add( 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 addafter(int num, int loc)
{
    int i;
    struct node *temp,*left,*right;
    right=head;
    for(i=1;i<loc;i++)
    {
    left=right;
    right=right->next;
    }
    temp=(struct node *)malloc(sizeof(struct node));
    temp->data=num;
    left->next=temp;
    left=temp;
    left->next=right;
    return;
}



void insert(int num)
{
    int c=0;
    struct node *temp;
    temp=head;
    if(temp==NULL)
    {
    add(num);
    }
    else
    {
    while(temp!=NULL)
    {
        if(temp->data<num)
        c++;
        temp=temp->next;
    }
    if(c==0)
        add(num);
    else if(c<count())
        addafter(num,++c);
    else
        append(num);
    }
}



int delete(int num)
{
    struct node *temp, *prev;
    temp=head;
    while(temp!=NULL)
    {
    if(temp->data==num)
    {
        if(temp==head)
        {
        head=temp->next;
        free(temp);
        return 1;
        }
        else
        {
        prev->next=temp->next;
        free(temp);
        return 1;
        }
    }
    else
    {
        prev=temp;
        temp= temp->next;
    }
    }
    return 0;
}


void  display(struct node *r)
{
    r=head;
    if(r==NULL)
    {
    return;
    }
    while(r!=NULL)
    {
    printf("%d ",r->data);
    r=r->next;
    }
    printf("\n");
}


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


int  main()
{
    int i,num;
    struct node *n;
    head=NULL;
    while(1)
    {
    printf("\nList Operations\n");
    printf("===============\n");
    printf("1.Insert\n");
    printf("2.Display\n");
    printf("3.Size\n");
    printf("4.Delete\n");
    printf("5.Exit\n");
    printf("Enter your choice : ");
    if(scanf("%d",&i)<=0){
        printf("Enter only an Integer\n");
        exit(0);
    } else {
        switch(i)
        {
        case 1:      printf("Enter the number to insert : ");
                 scanf("%d",&num);
                 insert(num);
                 break;
        case 2:     if(head==NULL)
                {
                printf("List is Empty\n");
                }
                else
                {
                printf("Element(s) in the list are : ");
                }
                display(n);
                break;
        case 3:     printf("Size of the list is %d\n",count());
                break;
        case 4:     if(head==NULL)
                printf("List is Empty\n");
                else{
                printf("Enter the number to delete : ");
                scanf("%d",&num);
                if(delete(num))
                    printf("%d deleted successfully\n",num);
                else
                    printf("%d not found in the list\n",num);
                }
                break;
        case 5:     return 0;
        default:    printf("Invalid option\n");
        }
    }
    }
    return 0;
}

Simple: sum all of the data values and divide by the number of nodes in the list. I am guessing that you did not write the functions to add/remove/size the list, etc. We don't do your homework for you. This is very much elementary math... :-(

yes i didnt write it ,i just want to learn the logics bout what if i sum all the data's and find the average.

yes i didnt write it ,i just want to learn the logics bout what if i sum all the data's and find the average.

???? What "logic" is there? Just do it. As mentioned, the average is the sum divided by the count. You already have a function that iterates through the list and gets the count. Use that as a template for a function that gets the sum. Add it to the menu. Now add a menu option for the average. For that function, find the sum (function will be already written) and find the count (function will already be written). Now divide.

By this point there will be one remaining obstacle. Suppose sum is 12 and count is 5. Average would be 2.4. But you are using integer division. You'll need to typecast at least one of those integers to be a double and store it in a double. See below.

double average = (double) sum() / count();

So, in summary, add a sum function based on your count function. Your average function is the single line above if you even want to bother having that be a function. If you do make it a function, just return the average variable. Now add the sum and average functions to your menu options. Assuming the rest of your program works, these are very small additions.

Comments
Well planed!
Wel explained.
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