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Questions about pointers in the linked list

fatemehsh (4)
I wrote a code using a linked list to store student information and functions add, delete, search and show it. When receiving a pointer to the first node is created first, and remains empty node address is not stored.
I appreciate your help, why is this happening?
The pointer first should not be null . Must store the address of the first node.


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#include<iostream>
#include<stdlib.h>
#include<string>


using namespace std;
class node{ 
int stnum;
float av;
string name;
public:
friend class linkedlist;
node *next;
};
class linkedlist{
public:
linkedlist(){first=NULL;}
void add();
void del(int);
void show();
void search(int);
private:
node *first;
node *last;
};
void linkedlist::add()
{
	if (first==NULL)
	{
		node *temp=new node;
		temp->next=NULL;
		first =temp;
		cout<<"please enter name , ave, student number:"<<"\n";
		cin>>temp->name>>temp->av>>temp->stnum;
		cout<<"\n";
		last=temp;
	}
	else
	{
        node *ptr=new node;
		cout<<"please enter name , ave, student number:"<<"\n";
		cin>>ptr->name>>ptr->av>>ptr->stnum;
		cout<<"\n";
		ptr->next=NULL;
		last->next=ptr;
		last=ptr;
	}
}
void linkedlist::del(int x)
{
	node *temp,*temp1;
	int sw=0;
	temp=temp1=first;
	if (first->stnum==x)
	{
		temp=first;
		first->next=first;
		delete temp;
		sw=1;
	}
	else
	{
		while (temp!=last)
		{
			temp=temp1->next;
			if(temp->stnum==x)
			{
			if (temp==last)
			{
				temp1->next=NULL;
				delete temp;
				last=temp1;
				sw=1;
				break;
			}
			else
			{
				temp1->next=temp->next;
				delete temp;
				sw=1;
				break;
			}
			}
		}
		temp1=temp1->next;
	}
	if(sw==0)
	{
		cout<<"No student with student number"<<" "<<x<<" "<<" \n";
	}
}
void linkedlist::show()
{
	if (first==NULL)
	{
		cout<<"No student\n";
	}
	else
	{
		node *temp;
		temp=first;
		while (temp!=NULL)
		{
			cout<<temp->name<<temp->stnum<<temp->av<<"\n";
			temp=temp->next;
		}
	}
}
void linkedlist::search(int x)
{
	node *temp,*temp1;
	temp=temp1=first;
	int sw=0;
	while (temp!=last)
	{
		temp=temp1->next;
		if (temp->stnum==x)
		{
			cout<<temp->name<<temp->av<<"\n";
			sw=1;
		}
	}
	temp1=temp1->next;
	if (sw==0)
		{
			cout<<"No student with student number"<<" "<<x<<" "<<" \n";
		}
}
int main(int argc, char* argv[])
{
	int a=0
        while(a==0){
		int s,h,m;
		class linkedlist l;
		cout<<"menu:\n";
		cout<<"add.................1\n";
		cout<<"delete..............2\n";
		cout<<"show................3\n";
		cout<<"search..............4\n";
		cin>>m;
		switch (m)
		{
		case 1:
			{
			    l.add();
			    break;
			}
		case 2:
			{
				cout<<"enter student number : \n";
				cin>>h;
				l.del(h);
				break;
			}
		case 3:
			{
				l.show();
				break;
			}
		case 4:
			{
				cout<<"enter student number : \n";
				cin>>s;
				l.search(s);
					break;
			}

		default:
			break;
		}
}
	
	
	system("PAUSE");
	return 0;
}
Last edited on
cire (8284)
I appreciate your help, why is this happening?
The pointer first should not be null . Must store the address of the first node.

You don't do anything but one operation with the list. What makes you think that operation isn't working?
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