Student Management System C++ - c++

Question

I have this program in C++ for Student Management System , Everything is working fine , except one place where i try to delete a student based on his roll number .
What it should do : After asking the roll number search the record and delete it
What is it doing : It deletes all the other records which do not match that roll number
Here is my code :
#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <conio.h>
#include <iomanip>
using namespace std;
int main() {
FILE *fp, *ft;
char another, choice;
struct student {
char first_name[50], last_name[50];
int roll_num; //new code added
char course[100];
int section;
};
struct student e;
char xfirst_name[50], xlast_name[50];
int xroll_num ; // new code added
long int recsize;
fp=fopen("users.txt","rb+");
if (fp == NULL) {
fp = fopen("users.txt","wb+");
if (fp==NULL)
{
puts("Cannot open file");
return 0;
}
}
recsize = sizeof(e);
while(1) {
system("cls");
cout << "\t\t====== STUDENT INFORMATION SYSTEM ======";
cout <<"\n\n ";
cout << "\n\n";
cout<<" \n\t\t\t======================";
cout << "\n \t\t\t 1. Add Records";
cout << "\n \t\t\t 2. List Records";
cout << "\n \t\t\t 3. Modify Records";
cout << "\n \t\t\t 4. Delete Records";
cout << "\n \t\t\t 5. Exit Program";
cout<<" \n\t\t\t======================";
cout << "\n\n";
cout << "\t\t\t Select Your Choice ::";
fflush(stdin);
choice = _getche();
switch(choice)
{
case '1' :
fseek(fp,0,SEEK_END);
another ='Y';
while(another == 'Y' || another == 'y')
{
system("cls");
cout << "Enter the First Name : ";
cin >> e.first_name;
cout << "Enter the Last Name : ";
cin >> e.last_name;
cout << "Enter the Course : ";
cin >> e.course;
cout << "Enter the Section : ";
cin >> e.section;
cout << "Enter the roll number :";
cin >> e.roll_num;
fwrite(&e,recsize,1,fp);
cout << "\n Add Another Record (Y/N) ";
fflush(stdin);
another = getchar();
}
break;
case '2':
system("cls");
rewind(fp);
cout << "=== View the Records in the Database ===";
cout << "\n";
while (fread(&e,recsize,1,fp) == 1){
cout << "\n";
cout <<"\nName :: " <<e.first_name <<" "<<e.last_name;
//cout << "\n";
cout <<"\nRoll Number :: " << e.roll_num ;
cout <<"\nCourse :: " <<e.course ;
cout <<"\nSection :: "<<e.section;
}
cout << "\n\n";
system("pause");
break;
case '3' :
system("cls");
another = 'Y';
while (another == 'Y'|| another == 'y')
{
// cout << "\n Enter the last name of the student : ";
cout << "\n Enter the Roll number of the student : ";
cin >> xroll_num;
rewind(fp);
while (fread(&e,recsize,1,fp) == 1)
{
//if (strcmp(e.last_name,xlast_name) == 0)
if(e.roll_num == xroll_num )
{
cout << "Enter the new Firt Name : ";
cin >> e.first_name;
cout << "Enter the new Last Name : ";
cin >> e.last_name;
cout << "Enter the new Roll Number : ";
cin >> e.roll_num;
cout << "Enter the new Course : ";
cin >> e.course;
cout << "Enter the new Section : ";
cin >> e.section;
fseek(fp, - recsize, SEEK_CUR);
fwrite(&e,recsize,1,fp);
break;
}
else
cout<<"record not found";
}
cout << "\n Modify Another Record (Y/N) ";
fflush(stdin);
another = getchar();
}
break;
case '4':
system("cls");
another = 'Y';
while (another == 'Y'|| another == 'y')
{
// cout << "\n Enter the last name of the student to delete : ";
cout <<"\n Enter the roll number of the student to delete : ";
cin >> xroll_num;
ft = fopen("temp.dat", "wb");
rewind(fp);
while (fread (&e, recsize,1,fp) == 1)
// if (strcmp(e.last_name,xlast_name) != 0)
if(e.roll_num == xroll_num )
{
fwrite(&e,recsize,1,ft);
}
fclose(fp);
fclose(ft);
remove("users.txt");
rename("temp.dat","users.txt");
fp=fopen("users.txt","rb+");
cout << "\n Delete Another Record (Y/N) ";
fflush(stdin);
another = getchar();
}
break;
case '5':
fclose(fp);
cout << "\n\n";
cout << "\t\t THANK YOU FOR USING THIS SOFTWARE";
cout << "\n\n";
exit(0);
}
}
system("pause");
return 0;
}

Answer 1

It deletes all the other records which do not match that roll number
Well you're only writing the records that match the roll number to the temp file, and then using that file to overwrite the users.txt file
if (e.roll_num == xroll_num) {
fwrite(&e, recsize, 1, ft);
}
I suppose what you really wanted to do is
if (e.roll_num != xroll_num) {
fwrite(&e, recsize, 1, ft);
}
You should probably read a good C++ i/o tutorial, as your code is mostly C. Consider writing your student struct as simple text instead of writing it wholesale to the file.