Access violation reading location 0xCCCCCCCC error in linklist - c++

Question

Why does the above error occur when calling showNode()?
#include<iostream>
#define NULL 0
using namespace std;
class myNode{
private:
int data;
myNode* link;
myNode* first;
public:
myNode(){
data=0;
link=NULL;
first=NULL;
}
void insertNode(int value, int iposition){
myNode n;
if (iposition==1)
{
first=&n;
cout<<first<<endl;
n.data=value;
n.link=NULL;
}
if (iposition>1)
{
int nodeCounter=1;
myNode* temp=first;
while (temp->link != NULL)
{
nodeCounter++;
}// this while counts the number of inserted nodes.
if (iposition>nodeCounter)//if the position of the new node is greater than number of inserted node,
//it will be inserted at the end.
{
cout<<"Node will be inserted at end."<<endl;
myNode* ieTemp=first;
while (ieTemp->link != NULL)
{
ieTemp=ieTemp->link;
cout<<ieTemp->data<<endl;
}
ieTemp->link=&n;
n.data=value;
n.link=NULL;
cout<<&n<<" ";
}
else
{
myNode* imTemp=first;
while (iposition-1)
{
imTemp=imTemp->link;
iposition--;
}
n.link=imTemp->link;
n.data=value;
imTemp->link=&n;
}
}
}//end insertNode
void showNode(){
myNode* sTemp=first;
while (sTemp != NULL)
{
cout<<sTemp->data<<" ";
sTemp=sTemp->link;
}
}//end showNode
};
int main(){
myNode a;
a.insertNode(10,1);
a.insertNode(20,2);
a.insertNode(25,3);
a.insertNode(30,4);
a.insertNode(40,5);
a.showNode();
system("pause");
}

Answer 1

First you must declare myNode *n = new myNode(); because you use it outside of insertNode function. Second you may want to check if first node exist to avoid error on inserting first node on any other position than 1 (in your case if your first insert will be like inserNode(x, y != 1) will throw an error because you try to access first node (here: while (temp->link != NULL))) but this node don't exist.
This is what I think you want:
void insertNode(int value, int iposition){
myNode *n = new myNode();
myNode *cur = first;
//insert first node or on first position
if (cur == NULL || iposition <= 1) {
n->data = value;
if (cur == NULL) { //first node
n->link = NULL;
}
else { //first position
n->link = first;
}
first = n;
return;
}
for (int i = 1; i < iposition - 1; i++) { //find given position
if (cur->link == NULL) { //if end
n->data = value;
n->link = NULL;
cur->link = n;
return;
}
cur = cur->link;
}
//here we are on position = iposition-1
n->data = value;
n->link = cur->link;
cur->link = n;
}//end insertNode