Program Freezes When Inserting A New Node To A Linked List

Question

I've made a function to insert a node to a linked list while preserving the list. However, after inserting 2 elements, if the next element is higher than all the others, the program seems to loop infinitely. My conditions show allow the program to break the loop if something happens but it doesn't;

Here's the function. Note that head is a pointer to the first element in the list and is NULL if the list is empty:

//defines the node structure
typedef struct node{

int n;
struct node* next;
}node;

bool insert_node(int value)
{
int t=0;


//If list is empty
if (head==NULL){
    node* first = malloc(sizeof(node));

    //error checking
    if (first==NULL)
        return false;

    head = first;
    first->n=value;
    first->next=NULL;
    t=1;
}

else{
    node* body=malloc(sizeof(node));
    if (body==NULL){
        t=9;
        return false;
        }

    body->n=value;
    node* ptr=head;
    node*pre=head;

    //putting new node into list
    while(t==0){
        //error checking
        if (ptr==NULL)
            break;

        //insertion
        else if (value<=ptr->n||ptr->next==NULL){
            body->next=ptr;
            pre->next=body;
            t=1;
        }

        //next node
        else if(value>ptr->n){
            pre=ptr;
            ptr=ptr->next;
        }

        //If all goes wrong
        else 
            t=9; //breaks loop
        }
    }

if (t==1)
    return true;

return false;
}

Answer 1

You need to handle the case where the entry that you are adding needs to be at the head of the list. Right now you only add to the head when the list is empty. That is handled by changing the if as follows:

if (head==NULL || value < head->n){
    node* first = malloc(sizeof(node));

    //error checking
    if (first==NULL)
        return false;

    first->next=head;
    first->n=value;
    head = first;
    t=1;
}

Now that the addition to the beginning of the list is taken care of, the else needs a change to get pre and ptr initialized correctly and the insertion condition needs to be changed as follows:

node* ptr=head->next;
node* pre=head;

//putting new node into list
while(t==0){
    //insertion
    if (ptr==NULL || value<=ptr->n){
        body->next=ptr;
        pre->next=body;
        t=1;
    }

    //next node
    else if(value>ptr->n){
        pre=ptr;
        ptr=ptr->next;
    }

    //If all goes wrong
    else 
        t=9; //breaks loop
    }
}