Can someone how to fix the error of this code the error is [error] expected unqualified-id before '{' token</pre>

#include <iostream>
#include <string>
#include <conio.h>
#include<fstream>
#include<iomanip>
 
using namespace std;

int main ()
{
	char ch;
	start:
    string userName;
    string userPassword;

    
    {
    	cout << "Welcom to Asian Institute of Computer studies\n\n";
        cout << "User name: ";
        cin >> userName;
        cout << "Password: ";
        ch = getch();
 
        while (ch !=13)
        {
		userPassword.push_back(ch);
		cout << '*';
		ch = getch();
		}

        if (userName == "Admin" && userPassword == "pulmano052802")
        {
        	cout << "\n\n";
        	cout << "ACCESS GRANTED\n";
            cout << "Welcome!\n";
            return 0;
        }
        else
        {
        	cout << "\n\n";
            cout << "ACCESS DENIED\n" << '\n';
            cout << "Invalid login attempt. Please try again.\n" << '\n';
            goto start;
        }
    }

    cout << "Thank you for logging in.\n";
    return 0;
}
class student
{
	int idnum;
	char name[50];
	int attendance, quiz, recitation, project, exam;
	double per,avg;
	char grade;
	void calculate();	
public:
	void getdata();		
	void showdata() const;	
	void show_tabular() const;
	int getIDNum() const;
}; 
void student::calculate()
{
	per = (attendance + quiz + recitation + project + exam )/5.0;
	avg = per;
	if(avg>=75.0 && avg <=100.0)
	cout<<"Grade rating: Passed\n\n\n";
	else if(avg>=1.0 && avg<=74.9)
    cout<<"Grade rating: Failed\n\n\n";
    
}
 
 

void student::getdata()
{
	cout<<"\nEnter The ID number of the student ";
	cin>>idnum;
	cout<<"\n\nEnter student's Name: ";
	cin.ignore();
	cin.getline(name,50);
	cout<<"\nEnter attendance grade: ";
	cin>>attendance;
	cout<<"\nEnter quiz grade: ";
	cin>>quiz;
	cout<<"\nEnter recitation grade: ";
	cin>>recitation;
	cout<<"\nEnter project grade: ";
	cin>>project;
	cout<<"\nEnter exam grade: ";
	cin>>exam;
	calculate();
}
 
void student::showdata() const
{
	cout<<"\nID Number: "<<idnum;
	cout<<"\nName: "<<name;
	cout<<"\nattendance: "<<attendance;
	cout<<"\nquiz: "<<quiz;
	cout<<"\nrecitation: "<<recitation;
	cout<<"\nproject: "<<project;
	cout<<"\nexam: "<<exam;
	cout<<"\nPercentage: "<<per;
	cout<<"\nGrade rating: "<<avg;

}
 
void student::show_tabular() const
{
	cout<<idnum<<setw(6)<<" "<<name<<setw(10)<<attendance<<setw(4)<<quiz<<setw(4)<<recitation<<setw(4)
		<<project<<setw(4)<<exam<<setw(8)<<per<<setw(6)<<avg<<endl;
}
 
int  student::getIDNum() const
{
	return idnum;
}
 
 
 
void SaveStudent();	
void displayAll();	
void Searchdisplay(int);	
void modifyStudent(int);	
void deleteStudent(int);	
void DisplayClassResult();	
void DisplayResult();			
	
 
 
 
 
void write_student()
{
	student st;
	ofstream outFile;
	outFile.open("student.dat",ios::binary|ios::app);
	st.getdata();
	outFile.write(reinterpret_cast<char *> (&st), sizeof(student));
	outFile.close();
    	cout<<"\n\nStudent record Has Been Created ";
	cin.ignore();
	cin.get();
}
 
 
 
void display_all()
{
	student st;
	ifstream inFile;
	inFile.open("student.dat",ios::binary);
	if(!inFile)
	{
		cout<<"File could not be open !! Press any Key...";
		cin.ignore();
		cin.get();
		return;
	}
	cout<<"\n\n\n\t\tDISPLAY ALL RECORD !!!\n\n";
	while(inFile.read(reinterpret_cast<char *> (&st), sizeof(student)))
	{
		st.showdata();
		cout<<"\n\n====================================\n";
	}
	inFile.close();
	cin.ignore();
	cin.get();
}
 
 
 
void display_sp(int n)
{
	student st;
	ifstream inFile;
	inFile.open("student.dat",ios::binary);
	if(!inFile)
	{
		cout<<"File could not be open !! Press any Key...";
		cin.ignore();
		cin.get();
		return;
	}
	bool flag=false;
	while(inFile.read(reinterpret_cast<char *> (&st), sizeof(student)))
	{
		if(st.getIDNum()==n)
		{
	  		 st.showdata();
			 flag=true;
		}
	}
	inFile.close();
	if(flag==false)
		cout<<"\n\nrecord not exist";
	cin.ignore();
	cin.get();
}
 
 
void modify_student(int n)
{
	bool found=false;
	student st;
	fstream File;
	File.open("student.dat",ios::binary|ios::in|ios::out);
	if(!File)
	{
		cout<<"File could not be open !! Press any Key...";
		cin.ignore();
		cin.get();
		return;
	}
    	while(!File.eof() && found==false)
	{
 
		File.read(reinterpret_cast<char *> (&st), sizeof(student));
		if(st.getIDNum()==n)
		{
			st.showdata();
			cout<<"\n\nPlease Enter The New Details of student"<<endl;
			st.getdata();
		    	int pos=(-1)*static_cast<int>(sizeof(st));
		    	File.seekp(pos,ios::cur);
		    	File.write(reinterpret_cast<char *> (&st), sizeof(student));
		    	cout<<"\n\n\t Record Updated";
		    	found=true;
		}
	}
	File.close();
	if(found==false)
		cout<<"\n\n Record Not Found ";
	cin.ignore();
	cin.get();
}
 
 
 
void delete_student(int n)
{
	student st;
	ifstream inFile;
	inFile.open("student.dat",ios::binary);
	if(!inFile)
	{
		cout<<"File could not be open !! Press any Key...";
		cin.ignore();
		cin.get();
		return;
	}
	ofstream outFile;
	outFile.open("Temp.dat",ios::out);
	inFile.seekg(0,ios::beg);
	while(inFile.read(reinterpret_cast<char *> (&st), sizeof(student)))
	{
		if(st.getIDNum()!=n)
		{
			outFile.write(reinterpret_cast<char *> (&st), sizeof(student));
		}
	}
	outFile.close();
	inFile.close();
	remove("student.dat");
	rename("Temp.dat","student.dat");
	cout<<"\n\n\tRecord Deleted ..";
	cin.ignore();
	cin.get();
}
 
 
void class_result()
{
	student st;
	ifstream inFile;
	inFile.open("student.dat",ios::binary);
	if(!inFile)
	{
		cout<<"File could not be open !! Press any Key...";
		cin.ignore();
		cin.get();
		return;
	}
	cout<<"\n\n\t\tALL STUDENTS RESULT \n\n";
	cout<<"==========================================================\n";
	cout<<"R.No       Name        P   C   M   E   CS   avg% "<<endl;
	cout<<"==========================================================\n";
	while(inFile.read(reinterpret_cast<char *> (&st), sizeof(student)))
	{
		st.show_tabular();
	}
	cin.ignore();
	cin.get();
	inFile.close();
}

{
	{
	char ch;
	int num;
	cout.setf(ios::fixed|ios::showpoint);
	cout<<setprecision(2); 
	do
	{
	system("cls");
	cout<<"\t**********************************************";
	cout<<"\n\n\t1.CREATE STUDENT RECORD";
	cout<<"\n\n\t2.DISPLAY ALL STUDENTS RECORDS";
	cout<<"\n\n\t3.SEARCH STUDENT RECORD ";
	cout<<"\n\n\t4.MODIFY STUDENT RECORD";
	cout<<"\n\n\t5.DELETE STUDENT RECORD";
	cout<<"\n\n\t6. DISPLAY CLASS RESULT";
	cout<<"\n\n\t7. EXIT";
	cout<<"\n\n\t*****************************************";
	cout<<"\n\n\tPlease Enter Your Choice (1-7): ";
	cin>>ch;
	system("cls");
	switch(ch)
	{
	case '1':	write_student(); break;
	case '2':	display_all(); break;
	case '3':	cout<<"\n\n\tPlease Enter Student's ID number: "; cin>>num;
				display_sp(num); break;
	case '4':	cout<<"\n\n\tPlease Enter Student's ID number: "; cin>>num;
			modify_student(num);break;
	case '5':	cout<<"\n\n\tPlease Enter Student's ID number: "; cin>>num;
			delete_student(num);break;
	case '6' :	class_result(); break;
	case '7':	exit(0);;
	default:	cout<<"\a"; 
		
    }
	}while(ch!='7');
 
	return 0;
}
}