How To Modify Data In a c++ Linked List - c++

Question

I have made a Student record system in c++ using the concept of linked list. The program will take the student id, name and marks for 3 different exams. Then it will calculate the aggregate percentage based on those exams marks and display the relevant message according to the aggregate percentage. The program is running without any errors.
But I want student id to be unique. For example, if a user inputs a student id which has been already assigned to previous student than it will show a message that "please enter a different id."
How would I do that. Any help will be appreciated.
struct student
{
int id;
char name[MAX];
string status;
double aggr;
int matric_marks, inter_marks, entryTest_marks;
};
struct node
{
struct student *data;
struct node *next;
node()
{
data = 0;
next = NULL;
}
};
struct student *readStudent()
{
clearWindow();
struct student *stdnt = new student;
gotoxy(33,8);cout<<"Student ID: ";
while(!(cin >> stdnt->id) || cin.peek() != '\n')
{
char ch;
cin.clear();
cout << "sorry";
while(cin.get(ch) && ch != '\n');
}
cin.ignore();
gotoxy(33,10);cout<<"Student Name: ";
cin.getline(stdnt->name, 50);
gotoxy(33,12);cout<<"Enter Matriculation Marks: ";
cin>>(stdnt->matric_marks);
gotoxy(33,14);cout<<"Enter Intermediate Marks: ";
cin>>(stdnt->inter_marks);
gotoxy(33,16);cout<<"Enter Entry Test Marks: ";
cin>>(stdnt->entryTest_marks);
stdnt->aggr = calculate_aggregiate(stdnt);
gotoxy(33,18);cout<<"Student Aggregate Marks: "<< stdnt->aggr;
if (stdnt->aggr >= 70)
{
gotoxy(33,20);cout<<"Student Registered In Electrical Engg";
}
else if (stdnt->aggr >= 60)
{
gotoxy(33,22);cout<<"Student Registered In Mechanical Engg";
}
else if (stdnt->aggr >=50)
{
gotoxy(33,24);cout<<"Student Registered In Computer Science";
}
else
{
gotoxy(33,20);cout<<"Sorry! The Student Doesnt Qualify";
}
return stdnt;
}
struct node *createDatabase(int size)
{
int i = 0;
struct node *head = NULL;
struct node *last = NULL;
for(i = 0; i < size; i++)
{
struct student *stdnt = readStudent();
struct node * current = new node;
current->data = stdnt;
current->next = NULL;
if(last)
last->next = current;
else
head = current;
last = current;
}
return head;
}
struct node *InsertRecord(struct node *head)
{
struct node *record = new node;
struct student *stdnt = readStudent();
record->data=stdnt;
record->next=head;
return record;
}
double calculate_aggregiate(struct student *stud)
{
student *stdnt = stud;
double aggr;
aggr = stdnt->matric_marks * 10/100 + stdnt->inter_marks * 50/100 +
stdnt->entryTest_marks * 40/100;
return aggr;
}
struct node *DeleteRecord(struct node *head)
{
clearWindow();
struct node *curr,*prev, *temp;
int tdata;
if(head==NULL)
{
gotoxy(33,10);cout<<"NO RECORDS TO DELETE......!";
}
else
{
gotoxy(33,10);cout<<"Enter Student ID To Be Deleted: ";
cin>>tdata;
prev=curr=head;
while((curr!=NULL)&&(curr->data->id!=tdata))
{
prev=curr;
curr=curr->next;
}
if(curr==NULL)
{
gotoxy(33,12);cout<<"The Requested ID Is Not Found...!";
}
else if(curr==head)
{
head=head->next;
gotoxy(33,12);cout<<"DATA DELETED....!";
}
else
{
prev->next=curr->next;
if(curr->next==NULL)
{
temp=prev;
}
gotoxy(33,12);cout<<"DATA DELETED....!"<<tdata;
}
delete(curr);
}
return head;
}
void ModifyRecord(struct node *head)
{
clearWindow();
int ch, sid;
struct node *current;
struct student *stdnt;
if (head==NULL)
{
gotoxy(33,8);cout<<"NO RECORD TO MODIFY..!";
}
else
{
gotoxy(33,8);cout<<"Enter Student ID To Modify: ";
cin>>sid;
current=head;
while((current!=NULL) && (current->data->id!=sid))
{
current=current->next;
}
if (current==NULL)
{
gotoxy(33,10);cout<<"The Requested ID is Not Found";
}
else if(current->data->id==sid)
{
gotoxy(33,10);cout<<"What Do You Want To Modify";
gotoxy(33,12);cout<<"1. Student's Name";
gotoxy(33,14);cout<<"2. Student's Matric Marks";
gotoxy(33,16);cout<<"3. Student's Intermediate Marks";
gotoxy(33,18);cout<<"4. Student's Entry Test Marks";
gotoxy(33,20);cout<<"Enter Your Choice: ";
cin>>ch;
switch(ch)
{
case 1 : gotoxy(33,22);cout<<"Enter New Name: ";
cin.getline(current->data->name, 50);break;
case 2 : gotoxy(33,22);cout<<"Enter New Matric Marks: ";
cin>>(current->data->matric_marks);break;
case 3 : gotoxy(33,22);cout<<"Enter New Intermediate Marks: ";
cin>>(current->data->inter_marks);break;
case 4 : gotoxy(33,22);cout<<"Enter New Entry Test Marks: ";
cin>>(current->data->entryTest_marks);break;
current->data->aggr = current->data->matric_marks * 10/100 + current->data- >inter_marks * 50/100 +
current->data->entryTest_marks * 40/100;
}
gotoxy(33,24);cout<<"RECORD MODIFIED....!";
}
}
}
void SearchRecord(struct node *head)
{
clearWindow();
int s_id;
struct node *current;
if (head==NULL)
{
gotoxy(33,8);cout<<"NO RECORD TO SEARCH..!";
}
else
{
gotoxy(33,8);cout<<"Enter Student ID To Be Searched: ";
cin>>s_id;
current=head;
while ((current!=NULL) && (current->data->id!=s_id))
{
current=current->next;
}
if (current==NULL)
{
gotoxy(33,10);cout<<"The Requested ID is Not Found";
}
else if (current->data->id==s_id)
{
gotoxy(33,10);cout<<"Student ID: "<<current->data->id;
gotoxy(33,12);cout<<"Student Name: "<<current->data->name;
gotoxy(33,14);cout<<"Student Matric Marks: "<<current->data->matric_marks;
gotoxy(33,16);cout<<"Student Intermediate Marks: "<<current->data - >inter_marks;
gotoxy(33,18);cout<<"Student Entry Test Marks: "<<current->data- >entryTest_marks;
gotoxy(33,20);cout<<"Student Aggregate Marks: "<<current->data->aggr;
if (current->data->aggr >= 70)
{
gotoxy(33,22);cout<<"Student Registered In Electrical Engg";
}
else if (current->data->aggr >= 60)
{
gotoxy(33,22);cout<<"Student Registered In Mechanical Engg";
}
else if (current->data->aggr >=50)
{
gotoxy(33,22);cout<<"Student Registered In Computer Science";
}
else
{
gotoxy(33,22);cout<<"Sorry! The Student Doesnt Qualify";
}
}
}
}
void print(struct node *head)
{
clearWindow_p();
struct node *current = head;
if (head == NULL)
{
gotoxy(33,8);cout<<"No Student Registered Yet......!";
}
else
{
cout<<"\n\t\t\t\t\tSTUDENTS STATISTICS";
while(current)
{
struct student *stdnt = current->data;
cout<<"\n\t\t\t\t\t-------------------------------- ";
cout<<"\n\t\t\t\t\tStudent ID :"<<stdnt->id;
cout<<"\n\t\t\t\t\tStudent Name :"<<stdnt->name;
cout<<"\n\t\t\t\t\tMatric Marks :"<<stdnt->matric_marks;
cout<<"\n\t\t\t\t\tIntermediate Marks :"<<stdnt->inter_marks;
cout<<"\n\t\t\t\t\tEntry Test Marks: "<<stdnt->entryTest_marks;
cout<<"\n\t\t\t\t\tAggregate: "<<stdnt->aggr;
if (stdnt->aggr >= 70)
{
cout<<"\n\t\t\t\t\tStudent Registered In Electrical Engg";
}
else if (stdnt->aggr >= 60)
{
cout<<"\n\t\t\t\t\tStudent Registered In Mechanical Engg";
}
else if (stdnt->aggr >=50)
{
cout<<"\n\t\t\t\t\tStudent Registered In Computer Science";
}
else
{
cout<<"\n\t\t\t\t\tSorry! The Student Doesnt Qualify";
}
current=current->next;
}
cout<<"\n\t\t\t\t\t--------------------------------";
}
}
int compareStudents(struct student *left, struct student *right)
{
return strcmp(left->name, right->name);
}
struct node *sort(struct node *head)
{
//using bubble sort
int swapped = 0;
do
{
swapped = 0;
struct node *current = head;
struct node *previous = NULL;
while(current && current->next)
{
if(compareStudents(current->data, current->next->data) > 0)
{
//swap here
struct node *next = current->next;
if(previous)
{
previous->next = next;
}
else
{
head = next;
}
current->next = next->next;
previous = next;
previous->next = current;
swapped = 1;
}
else
{
previous = current;
current = current->next;
}
}
} while(swapped);
return head;
}
int main()
{
system("color f0");
window();
SetColor(28);
int total,i,choice;
int x = 2;
struct node *head;
head=NULL;
do
{
menu:
gotoxy(x, 8);cout<<"1.Create a Record File";
gotoxy(x, 10);cout<<"2.Insert Student's Record";
gotoxy(x, 12);cout<<"3.Modify Student's Record";
gotoxy(x, 14);cout<<"4.Delete Student's Record";
gotoxy(x, 16);cout<<"5.Search Student's Record";
gotoxy(x, 18);cout<<"6.Print All Records";
gotoxy(x, 20);cout<<"7.Sort According To Names";
gotoxy(x, 22);cout<<"8.Clear The Screen";
gotoxy(x, 24);cout<<"9.Exit";
gotoxy(x, 26);cout<<"Enter your choice";
cout<<" [ ]\b\b";
cin>>choice;
switch(choice)
{
case 1:
clearWindow();
gotoxy(33, 8);cout<<"How Many Students Do You Want To Register: ";
cin>>total;
head=createDatabase(total);
break;
case 2:
head=InsertRecord(head);
break;
case 3:
ModifyRecord(head);
break;
case 4:
DeleteRecord(head);
break;
case 5:
SearchRecord(head);
break;
case 6:
print(head);
break;
case 7:
sort(head);
print(head);
break;
case 8:
main();
break;
default: gotoxy(33,8);cout<<"INVALID OPTION";
}
}while(choice!=9);
getch();
return 0;
}

Answer 1

Since you are using C++, you should take advantage of the built-in types. If there is only one student with a given ID, use the std::map<> template. For example:
struct student
{
char name[MAX];
string status;
double aggr;
int matric_marks, inter_marks, entryTest_marks;
};
map<int, student> students;
then, to traverse students:
for (auto i = students.begin(); i != students.end(); ++i) {
int studentId = i->first;
student& student = i->second;
student.aggr = ...
}
(auto is C++11, not all compilers enable it by default IIRC. See here.)

Answer 2

If You know the range of student ids , and it is within a feasible range of memory , you can use a UsedId[] array.
If the range is too big too be held , use a Hashmap ,(MAP in c++) .

Answer 3

I would probably implement something called FindRecordByID.
struct student *FindRecordByID(struct node *head, int id) {
for(; head != NULL; head = head->next)
if (head->data->id == id)
return head->data;
return NULL;
}
Then when you do your create_new_student routine, you could use that to verify that the given ID is not already used.