Thread: Adding Students to a database

Im trying to add users to a student database.

When i try to add it lets me enter 4 of 5 items then crashes.

Any ideas?

Code below:

Code:

#include <iostream.h>
#include <conio.h>
#include <ctype.h>
#include <stdio.h>
#include <string.h>

#define NO_OF_STUDENTS 20

struct student_type
{
		 char  reg[20];
		 char  surname[25];
		 char  firstname[25];
		 char  phone;
		 int  credit;
};

void     initialise_data(student_type[]);
void             add_car(student_type[]);
void       show_all_cars(student_type[]);
void           save_data(student_type[]);
void            show_car(student_type[], int);


void main()
{
	student_type  cars[NO_OF_STUDENTS];
	char choice;
    	                                // Load car file into database
	initialise_data(cars);
                                      // Display menu and get user choice
	do
	{
		cout << "\n\n"
			  << "\nAdd a Student \t\t\tA"
			  << "\nShow all Students \t\tS"
			  << "\nFind a Student \t\t\tF"
           << "\n	Quit \t\t\tQ"
           << "\n\nChoice:- ";
		cin  >>  choice;
      choice = toupper(choice);

		switch (choice)
		{
			case 'A':
						add_car(cars);
						break;
      	case 'S':
						show_all_cars(cars);
						break;
		}
	} while (choice != 'Q');
}


void initialise_data(student_type cars[])
                                      // Loads car database from file
{
	int i, count = 0;
	FILE *in_file;

	for (i = 0; i < NO_OF_STUDENTS; i++)
		cars[i].phone = 0;

	in_file = fopen("cars.dat", "rb");

	if (in_file == NULL)
   	 cout << "Starting a new data file\n";
	else
		                               // If the file did open - read the data
		                               // After this 'count' will contain the
                                     // number of car records read.
		 count = fread(cars, sizeof(student_type), NO_OF_STUDENTS, in_file);

	fclose(in_file);

	cout << "\nNo of Students on file is " << count;
}

void add_car(student_type cars[])
											// Create a new car record in the database
{
	int next;


                                  // Count how many cars already in database
	for (next = 0; next < NO_OF_STUDENTS && cars[next].phone > 0; next++);

	if (next < NO_OF_STUDENTS)         // If database is not full, add a car
	{
		cout << "\nRegistration Number:   ";
		cin  >> cars[next].reg;
		cout <<   "Surname: ";
		cin  >> cars[next].surname;
		cout <<   "First Name:    ";
		cin  >> cars[next].firstname;
		cout <<   "Phone:   ";
		cin  >> cars[next].phone;
		cout <<	  "Credits:   ";
		cin  >> cars[next].credit;
	}
	else                           // If database is full, give message
		cout << "No room for any more Students\a\n";
	                               // Database has changed so save it
	save_data(cars);
}

void show_car(student_type cars[], int position)
                                  // Display any car knowing its array position
{
	cout << "\n\nRegistration Number:-  " << cars[position].reg;
	cout <<   "\nSurname:- " << cars[position].surname;
	cout <<   "\nFirst Name:-   " << cars[position].firstname;
    cout <<   "\nPhone:-  " << cars[position].phone;
	cout <<	  "\nCredits:-  " << cars[position].credit;
}

void show_all_cars(student_type cars[])
                                  // Display all cars by calls to show_car()
{
   for (int i = 0; i < NO_OF_STUDENTS && cars[i].phone > 0; i++)
		show_car(cars, i);
}

void save_data(student_type cars[])
                                  // Save database to disk after each change
{
	FILE *out_file;
	int i;

	out_file = fopen("cars.dat", "wb");

	for (i = 0; i < NO_OF_STUDENTS && cars[i].phone > 0; i++)
		fwrite(&cars[i], sizeof(student_type), 1, out_file);

	fclose(out_file);
}

Well step 1 is read the forum anouncements and use [code][/code]Tags

I didn't have any problems adding students. However, when you save, be sure to save your count first since you're expecting this when you load the file.

Code:

void save_data(student_type cars[])
                                  // Save database to disk after each change
{
	FILE *out_file;
	int i;

	out_file = fopen("cars.dat", "wb");

	// Write out the number of students

	for (i = 0; i < NO_OF_STUDENTS && cars[i].phone > 0; i++)
		fwrite(&cars[i], sizeof(student_type), 1, out_file);

	fclose(out_file);
}

In addition, you probably want to change the void main to an int main, since you'll be bugged about that 'til kingdom come. Also, you may want to change this:

Code:

#include <iostream.h>
#include <conio.h>
#include <ctype.h>
#include <stdio.h>
#include <string.h>

to this:

Code:

#include <iostream>
#include <stdio.h>
/*
#include <conio.h> //nothing used from this one
#include <ctype.h> //or this one
#include <string.h> //or this one
*/

using std::cout;
using std::cin;

<iostream.h> is a deprecated header file. <iostream> is the same thing except everything is in the std namespace instead of the global namespace.

You could also consider using a struct to hold the count and your array, since you don't really need to compute the count.

Code:

struct student_db_type
{
	student_type cars[NO_OF_STUDENTS];
	int count;
};

Load the count from the file, and then just increment the count when you add a record, and your count will be up-to-date.