linked list not working

[hdyh]

I just want to make a linked list program that can insert node, delete node, find node and display all the node, but i was not expert in program. i have tried to make a coding based on note, but it does not work. Help me solve this problem please.

  
#include <iostream>
using namespace std;

class Node {
	public:
	double data;
	Node *next;
};

class List{
	Node* head;
	public:
	int InsertNode (double x);
	int FindNode (double x);
	int DeleteNode (double x);
	void DisplayList (void);
};
	int List::InsertNode(double x) {
	int currIndex = 0;
    Node* currNode = head; 
	Node* prevNode = NULL; 
	while (currNode && x > currNode-> data) {
         prevNode = currNode;
         currNode = currNode->next; 
		 currIndex++; 
		 }	
		 
	Node* newNode = new Node; 
	newNode->data = x; 
	if (currIndex == 0) { 
	newNode->next = head; 
	head = newNode; 
	} 
	else { 
	newNode->next = prevNode->next; 
	prevNode->next = newNode; 
	} 
	return 0;
}

int List::FindNode(double x) {
	Node* currNode = head;
	int currIndex = 1;
	while (currNode && currNode->data != x) {
	currNode = currNode->next;
	currIndex++;	
	}
		if (currNode)
		return currIndex;
		else
		return 0;
	}
	
int List::DeleteNode(double x) {	
	Node* prevNode = NULL;
	Node* currNode = head;
	int currIndex = 1;
	while (currNode && currNode->data != x) {
	prevNode = currNode;
	currNode = currNode->next;
	currIndex++;
	}
		if (currNode) {
		if (prevNode) {
		prevNode->next = currNode->next;
		delete currNode;
	}
		else {
		head = currNode->next;
		delete currNode;
	}
	return currIndex;
	}
return 0;
}

void List::DisplayList() 
{ 
	int num = 0; 
	Node* currNode = head; 
	while (currNode != NULL){ 
	cout << currNode->data << endl; 
	currNode = currNode->next; 
	num++; 
	} 
	cout << "Number of nodes in the list: " << num << endl;
}

int main(void)
{
	//int num;
	//cout<<"how many data  :";
	//cin >>num;
	
	List list; 
	list.InsertNode(7); // successful 
	list.InsertNode(5); // successful 
	list.InsertNode(6); // successful 
	list.InsertNode(4); // successful // print all the elements 
	list.DisplayList(); 
	if(list.FindNode(5) > 0) cout << "5 found" << endl; 
	else 
	cout << "5 not found" << endl; 
	if(list.FindNode(4) > 0) cout << "4 found" << endl; 
	else 
	cout << "4 not found" << endl; 
	list.DeleteNode(7); 
	list.DisplayList(); 
	return 0; 
	}