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Linked List Delete won't work

closed account (oj1C54Gy)
I was task to create a linked list and it must be menu driven I already finish the other parts but the delete a record won't work and it just delete the first node and I to add a menu where a node is updated

Here's the code
#include <iostream>
#include <string>
using namespace std;

// Node Class
class Node {
public:
int roll;
string Name;
string Dept;
int Marks;
Node* next;
};

// Stores the head of the Linked List
Node* head = new Node();

// Check Function to check that if
// Record Already Exist or Not
bool check(int x)
{
// Base Case
if (head == NULL)
return false;

Node* t = new Node;
t = head;

// Traverse the Linked List
while (t != NULL) {
if (t->roll == x)
return true;
t = t->next;
}

return false;
}

// Function to insert the record
void Insert_Record(int roll, string Name,
string Dept, int Marks)
{
// if Record Already Exist
if (check(roll)) {
cout << "Student with this "
<< "record Already Exists\n";
return;
}

// Create new Node to Insert Record
Node* t = new Node();
t->roll = roll;
t->Name = Name;
t->Dept = Dept;
t->Marks = Marks;
t->next = NULL;

// Insert at Begin
if (head == NULL
|| (head->roll >= t->roll)) {
t->next = head;
head = t;
}

// Insert at middle or End
else {
Node* c = head;
while (c->next != NULL
&& c->next->roll < t->roll) {
c = c->next;
}
t->next = c->next;
c->next = t;
}

cout << "Record Inserted "
<< "Successfully\n";
}

// Function to search record for any
// students Record with roll number
void Search_Record(int roll)
{
// if head is NULL
if (!head) {
cout << "No such Record "
<< "Available\n";
return;
}

// Otherwise
else {
Node* p = head;
while (p) {
if (p->roll == roll) {
cout << "Roll Nmuber\t"
<< p->roll << endl;
cout << "Name\t\t"
<< p->Name << endl;
cout << "Department\t"
<< p->Dept << endl;
cout << "Marks\t\t"
<< p->Marks << endl;
return;
}
p = p->next;
}

if (p == NULL)
cout << "No such Record "
<< "Available\n";
}
}

// Function to delete record students
// record with given roll number
// if it exist
int Delete_Record(int roll)
{
Node* t = head;
Node* p = NULL;

// Deletion at Begin
if (t != NULL
&& t->roll == roll) {
head = t->next;
delete t;

cout << "Record Deleted "
<< "Successfully\n";
return 0;
}

// Deletion Other than Begin
while (t != NULL && t->roll != roll) {
p = t;
t = t->next;
}
if (t == NULL) {
cout << "Record does not Exist\n";
return -1;
p->next = t->next;

delete t;
cout << "Record Deleted "
<< "Successfully\n";

return 0;
}
}

// Function to display the Student's
// Record
void Show_Record()
{
Node* p = head;
if (p == NULL) {
cout << "No Record "
<< "Available\n";
}
else {
cout << "Index\tName\tCourse"
<< "\tMarks\n";

// Until p is not NULL
while (p != NULL) {
cout << p->roll << " \t"
<< p->Name << "\t"
<< p->Dept << "\t"
<< p->Marks << endl;
p = p->next;
}
}
}

// Driver code
int main()
{
head = NULL;
string Name, Course;
int Roll, Marks;

// Menu-driven program
while (true) {
cout << "\n\t\tWelcome to Student Record "
"Management System\n\n\tPress\n\t1 to "
"create a new Record\n\t2 to delete a "
"student record\n\t3 to Search a Student "
"Record\n\t4 to view all students "
"record\n\t5 to Exit\n";
cout << "\nEnter your Choice\n";
int Choice;

// Enter Choice
cin >> Choice;
if (Choice == 1) {
cout << "Enter Name of Student\n";
cin >> Name;
cout << "Enter Roll Number of Student\n";
cin >> Roll;
cout << "Enter Course of Student \n";
cin >> Course;
cout << "Enter Total Marks of Student\n";
cin >> Marks;
Insert_Record(Roll, Name, Course, Marks);
}
else if (Choice == 2) {
cout << "Enter Roll Number of Student whose "
"record is to be deleted\n";
cin >> Roll;
Delete_Record(Roll);
}
else if (Choice == 3) {
cout << "Enter Roll Number of Student whose "
"record you want to Search\n";
cin >> Roll;
Search_Record(Roll);
}
else if (Choice == 4) {
Show_Record();
}
else if (Choice == 5) {
exit(0);
}
else {
cout << "Invalid Choice "
<< "Try Again\n";
}
}
return 0;
}
Last edited on
kbw (9488)
You really should format your code. I've done that so I can see it, so I may as well post it.
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#include <iostream>
#include <string>
using namespace std;

// Node Class
class Node {
public:
    int roll;
    string Name;
    string Dept;
    int Marks;
    Node* next;
};

// Stores the head of the Linked List
Node* head = new Node();

// Check Function to check that if
// Record Already Exist or Not
bool check(int x)
{
    // Base Case
    if (head == NULL)
        return false;

    Node* t = new Node;
    t = head;

    // Traverse the Linked List
    while (t != NULL) {
        if (t->roll == x)
            return true;
        t = t->next;
    }

    return false;
}

// Function to insert the record
void Insert_Record(int roll, string Name, string Dept, int Marks)
{
    // if Record Already Exist
    if (check(roll)) {
        cout << "Student with this "
        << "record Already Exists\n";
        return;
    }

    // Create new Node to Insert Record
    Node* t = new Node();
    t->roll = roll;
    t->Name = Name;
    t->Dept = Dept;
    t->Marks = Marks;
    t->next = NULL;

    // Insert at Begin
    if (head == NULL || (head->roll >= t->roll)) {
        t->next = head;
        head = t;
    }

    // Insert at middle or End
    else {
        Node* c = head;
        while (c->next != NULL && c->next->roll < t->roll) {
            c = c->next;
        }
        t->next = c->next;
        c->next = t;
    }

    cout << "Record Inserted " << "Successfully\n";
}

// Function to search record for any
// students Record with roll number
void Search_Record(int roll)
{
    // if head is NULL
    if (!head) {
        cout << "No such Record " << "Available\n";
        return;
    }

    // Otherwise
    else {
        Node* p = head;
        while (p) {
            if (p->roll == roll) {
                cout << "Roll Nmuber\t" << p->roll << endl;
                cout << "Name\t\t" << p->Name << endl;
                cout << "Department\t" << p->Dept << endl;
                cout << "Marks\t\t" << p->Marks << endl;
                return;
            }
            p = p->next;
        }

        if (p == NULL)
            cout << "No such Record " << "Available\n";
    }
}

// Function to delete record students
// record with given roll number
// if it exist
int Delete_Record(int roll)
{
    Node* t = head;
    Node* p = NULL;

    // Deletion at Begin
    if (t != NULL && t->roll == roll) {
        head = t->next;
        delete t;

        cout << "Record Deleted " << "Successfully\n";
        return 0;
    }

    // Deletion Other than Begin
    while (t != NULL && t->roll != roll) {
        p = t;
        t = t->next;
    }
    if (t == NULL) {
        cout << "Record does not Exist\n";
        return -1;
        p->next = t->next;

        delete t;
        cout << "Record Deleted " << "Successfully\n";

        return 0;
    }
}

// Function to display the Student's
// Record
void Show_Record()
{
    Node* p = head;
    if (p == NULL) {
        cout << "No Record " << "Available\n";
    }
    else {
        cout << "Index\tName\tCourse" << "\tMarks\n";

        // Until p is not NULL
        while (p != NULL) {
            cout << p->roll << " \t"  p->Name << "\t" << p->Dept << "\t" << p->Marks << endl;
            p = p->next;
        }
    }
}

// Driver code
int main()
{
    head = NULL;
    string Name, Course;
    int Roll, Marks;

    // Menu-driven program
    while (true) {
        cout << "\n\t\tWelcome to Student Record "
            "Management System\n\n\tPress\n\t1 to "
            "create a new Record\n\t2 to delete a "
            "student record\n\t3 to Search a Student "
            "Record\n\t4 to view all students "
            "record\n\t5 to Exit\n";
        cout << "\nEnter your Choice\n";
        int Choice;

        // Enter Choice
        cin >> Choice;
        if (Choice == 1) {
            cout << "Enter Name of Student\n";
            cin >> Name;
            cout << "Enter Roll Number of Student\n";
            cin >> Roll;
            cout << "Enter Course of Student \n";
            cin >> Course;
            cout << "Enter Total Marks of Student\n";
            cin >> Marks;
            Insert_Record(Roll, Name, Course, Marks);
        }
        else if (Choice == 2) {
            cout << "Enter Roll Number of Student whose " "record is to be deleted\n";
            cin >> Roll;
            Delete_Record(Roll);
        }
        else if (Choice == 3) {
            cout << "Enter Roll Number of Student whose " "record you want to Search\n";
            cin >> Roll;
            Search_Record(Roll);
        }
        else if (Choice == 4) {
            Show_Record();
        }
        else if (Choice == 5) {
            exit(0);
        }
        else {
            cout << "Invalid Choice " << "Try Again\n";
        }
    }
    return 0;
}

Your code:
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Node* head = new Node();
//
int main() {
    head = NULL;
leaks that memory. It should just be:
 
 
Node* head = nullptr;

Your Delete_Record seems to be missing a few lines. I've highlighted the missing lines in bold on lines 23/24. I haven't checked if it's correct, but looks right at first sight:
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int Delete_Record(int roll)
{
    Node* t = head;
    Node* p = NULL;

    // Deletion at Begin
    if (t != NULL && t->roll == roll) {
        head = t->next;
        delete t;

        cout << "Record Deleted " << "Successfully\n";
        return 0;
    }

    // Deletion Other than Begin
    while (t != NULL && t->roll != roll) {
        p = t;
        t = t->next;
    }
    if (t == NULL) {
        cout << "Record does not Exist\n";
        return -1;
    }
    else {
        p->next = t->next;

        delete t;
        cout << "Record Deleted " << "Successfully\n";

        return 0;
    }
}
Last edited on
seeplus (6599)
Consider:

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#include <iostream>
#include <string>
using namespace std;

// Node Class
class Node {
public:
	int roll {};
	string Name;
	string Dept;
	int Marks {};
	Node* next {};

	Node() {}
	Node(int r, const std::string& n, const std::string& d, int m) : roll(r), Name(n), Dept(d), Marks(m) {}
};

// Stores the head of the Linked List
Node* head {};

// Check Function to check that if
// Record Already Exist or Not
bool check(int x) {
	// Traverse the Linked List
	for (auto t {head}; t; t = t->next)
		if (t->roll == x)
			return true;

	return false;
}

// Function to insert the record
void Insert_Record(int roll, const string& Name, const string& Dept, int Marks) {
	// if Record Already Exist
	if (check(roll)) {
		cout << "Student with this record already exists\n";
		return;
	}

	// Create new Node to Insert Record
	auto t {new Node(roll, Name, Dept, Marks)};

	if (!head || (head->roll >= t->roll)) {
		// Insert at Begin
		t->next = head;
		head = t;
	} else {
		// Insert at middle or End
		auto c {head};

		for (; c->next && c->next->roll < t->roll; c = c->next);

		t->next = c->next;
		c->next = t;
	}

	cout << "Record Inserted Successfully\n";
}

// Function to search record for any
// students Record with roll number
void Search_Record(int roll)
{
	for (auto p {head}; p; p = p->next)
		if (p->roll == roll) {
			cout << "Roll Nmuber\t" << p->roll << '\n';
			cout << "Name\t\t" << p->Name << '\n';
			cout << "Department\t" << p->Dept << '\n';
			cout << "Marks\t\t" << p->Marks << '\n';
			return;
		}

	cout << "No such Record Available\n";
	return;
}

// Function to delete record students
// record with given roll number
// if it exist
bool Delete_Record(int roll)
{
	auto t {head};

	// Deletion at Begin
	if (t && t->roll == roll) {
		head = t->next;
		delete t;
		return (cout << "Record Deleted Successfully\n"), true;
	}

	// Deletion Other than Begin
	Node* p {};

	for (; t && t->roll != roll; t = t->next)
		p = t;

	if (!t)
		return (cout << "Record does not Exist\n"), false;

	p->next = t->next;
	delete t;
	return (cout << "Record Deleted Successfully\n"), true;
}

// Function to display the Student's
// Record
void Show_Record()
{
	auto p {head};

	if (!p)
		cout << "No Record Available\n";
	else {
		cout << "Index\tName\tCourse" << "\tMarks\n";

		// Until p is not NULL
		for (; p; p = p->next)
			cout << p->roll << " \t" << p->Name << "\t" << p->Dept << "\t" << p->Marks << '\n';
	}
}

// Driver code
int main()
{
	// Menu-driven program

	for (bool quit {false}; !quit; ) {
		cout << "\n\t\tWelcome to Student Record "
			"Management System\n\n\tPress\n\t1 to "
			"create a new Record\n\t2 to delete a "
			"student record\n\t3 to Search a Student "
			"Record\n\t4 to view all students "
			"record\n\t5 to Exit\n";

		cout << "\nEnter your Choice: ";
		int Choice {};

		// Enter Choice
		cin >> Choice;

		switch (Choice) {
			case 1:
			{
				std::string Name, Course;
				int Roll {}, Marks {};

				cout << "Enter Name of Student: ";
				cin >> Name;

				cout << "Enter Roll Number of Student: ";
				cin >> Roll;

				cout << "Enter Course of Student: ";
				cin >> Course;

				cout << "Enter Total Marks of Student: ";
				cin >> Marks;

				Insert_Record(Roll, Name, Course, Marks);
			}
			break;

			case 2:
			{
				int Roll {};

				cout << "Enter Roll Number of Student whose record is to be deleted: ";
				cin >> Roll;

				Delete_Record(Roll);
			}
			break;

			case 3:
			{
				int Roll {};

				cout << "Enter Roll Number of Student whose record you want to Search: ";
				cin >> Roll;

				Search_Record(Roll);
			}
			break;

			case 4:
				Show_Record();
				break;

			case 5:
				quit = true;
				break;

			default:
				cout << "Invalid Choice Try Again\n";
				break;
		}
	}
}

The Grey Wolf (171)
The OP has already closed his account. 🤷‍♂️
seeplus (6599)
Well someone else might get some benefit from the code......
kbw (9488)
... at least he didn't delete his post. I was half expecting it, that's why I copied it.
dhayden (5798)
In case anyone in the same class is following along...

Notice that check(), Insert_Record(), Delete_Record(), and Search_Record() all look for the record. Let's factor out that code into:
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// Find the node whose roll is the given one.
// Return a reference to the pointer to the node,
// or a reference to the pointer to where the node should
// go.
Node * &find(int roll)

This returns a reference to to node pointer: either head, or some node's next pointer. It has the advantage of stopping when it knows it knows it has passed where the record should be. Building on seeplus's code:

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#include <iostream>
#include <string>
using namespace std;

// Node Class
class Node {
  public:
    int roll {};
    string Name;
    string Dept;
    int Marks {};
    Node *next {};

    Node() {}
    Node(int r, const std::string & n, const std::string & d, int m):roll(r), Name(n),
	Dept(d), Marks(m) {}
};

// Stores the head of the Linked List
Node *head {};

// Find the node whose roll is the given one.
// Return a reference to the pointer to the node,
// or a reference to the pointer to where the node should
// go.
Node * &
find(int roll)
{
    Node **pp, *p;
    for (pp = &head; (p = *pp); pp = &(p->next)) {
	if (p->roll >= roll) break;
    }
    return *pp;
}

// Check Function to check that if
// Record Already Exist or Not
bool
check(int x)
{
    // Traverse the Linked List
    Node *p = find(x);
    return p && p->roll == x;
}

// Function to insert the record
void
Insert_Record(int roll, const string & Name, const string & Dept, int Marks)
{
    // if Record Already Exist
    Node * &p {find(roll)};
    if (p && p->roll == roll) {
	cout << "Student with this record already exists\n";
	return;
    }
    // Create new Node to Insert Record
    auto t {new Node(roll, Name, Dept, Marks)};

    // Link it in
    t->next = p;
    p = t;
    cout << "Record Inserted Successfully\n";
}

// Function to search record for any
// students Record with roll number
void
Search_Record(int roll)
{
    Node *p = find(roll);
    if (p && p->roll == roll) {
	cout << "Roll Nmuber\t" << p->roll << '\n';
	cout << "Name\t\t" << p->Name << '\n';
	cout << "Department\t" << p->Dept << '\n';
	cout << "Marks\t\t" << p->Marks << '\n';
	return;
    }

    cout << "No such Record Available\n";
}

// Function to delete record students
// record with given roll number
// if it exist
bool
Delete_Record(int roll)
{
    Node * &p = find(roll);
    if (p && p->roll == roll) {
	Node *old = p;
	p = p->next;
	delete old;
	cout << "Record Deleted Successfully\n";
	return true;
    }
    
    cout << "Record does not Exist\n";
    return  false;
}

// Function to display the Student's
// Record
void
Show_Record()
{
    auto p {head};

    if (!p)
	cout << "No Record Available\n";
    else {
	cout << "Index\tName\tCourse" << "\tMarks\n";

	// Until p is not NULL
	for (; p; p = p->next)
	    cout << p->roll << " \t" << p->Name << "\t" << p->Dept
		 << "\t" << p->Marks << '\n';
    }
}

// Driver code
int
main()
{
    // Menu-driven program

    for (bool quit {false}; !quit;) {
	cout << "\n\t\tWelcome to Student Record "
	    "Management System\n\n\tPress\n\t1 to "
	    "create a new Record\n\t2 to delete a "
	    "student record\n\t3 to Search a Student "
	    "Record\n\t4 to view all students " "record\n\t5 to Exit\n";

	cout << "\nEnter your Choice: ";
	int Choice {};

	// Enter Choice
	cin >> Choice;

	switch (Choice) {
	case 1:
	    {
		std::string Name, Course;
		int Roll {}, Marks {};

		cout << "Enter Name of Student: ";
		cin >> Name;

		cout << "Enter Roll Number of Student: ";
		cin >> Roll;

		cout << "Enter Course of Student: ";
		cin >> Course;

		cout << "Enter Total Marks of Student: ";
		cin >> Marks;

		Insert_Record(Roll, Name, Course, Marks);
	    }
	    break;

	case 2:
	    {
		int Roll {};

		cout << "Enter Roll Number of Student whose record is to be deleted: ";
		cin >> Roll;

		Delete_Record(Roll);
	    }
	    break;

	case 3:
	    {
		int Roll {};

		cout << "Enter Roll Number of Student whose record you want to Search: ";
		cin >> Roll;

		Search_Record(Roll);
	    }
	    break;

	case 4:
	    Show_Record();
	    break;

	case 5:
	    quit = true;
	    break;

	default:
	    cout << "Invalid Choice Try Again\n";
	    break;
	}
    }
}

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