I have written the below program for a homework and am really stuggling to find out how to do the email verification. Could anyone please help? (I have looked online and in the text book).

Thanks so much.

program DataInput;



uses
  Classes,
  SysUtils,
  crt;

var

  sname:  string[15];
  fname:  string[15];
  Height: real;
  salary: currency;
  gender: char;
  tel:    string;
  email:  string;
  veg:    char;




begin
  writeln('This is a verification software');
  sleep(1000);
  clrscr;
  writeln('Please enter your surname');
  writeln;
  readln(sname);
  sleep(500);
  clrscr;
  writeln('  Surname:  ', sname);
  writeln('---------------------------------------------------------------------');
  writeln;
  writeln('Please enter your First name');
  writeln;
  readln(fname);
  sleep(500);
  clrscr;
  writeln;
  writeln('  First Name: ', fname);
  writeln('  Surname:    ', sname);
  writeln('---------------------------------------------------------------------');
  writeln;
  writeln('Please enter your height in cm');
  writeln;
  readln(Height);
  sleep(500);
  clrscr;
  writeln('  First Name: ', fname);
  writeln('  Surname:    ', sname);
  writeln('  Height:     ', Height: 0: 2, 'cm');
  writeln('---------------------------------------------------------------------');
  writeln;
  writeln('Please enter your salary (in GBP per annum) - please do not use symbols');
  writeln;
  readln(Salary);
  sleep(500);
  clrscr;
  writeln(' First Name: ', fname, '');
  writeln(' Surname:    ', sname, '');
  writeln(' Height:     ', Height: 0: 2, 'cm');
  writeln(' Salary:     ', chr(156), Salary: 0: 2);
  writeln('---------------------------------------------------------------------');
  writeln;
  writeln('Please enter your gender, either ''m''(male) or ''f''(female) ');
  writeln;
  readln(gender);
  sleep(500);
  clrscr;
  writeln(' First Name: ', fname, '');
  writeln(' Surname:    ', sname, '');
  writeln(' Height:     ', Height: 0: 2, 'cm');
  writeln(' Salary:     ', chr(156), Salary: 0: 2);

  if upcase(gender) = 'M' then
    writeln(' Gender:     Male')
  else
    writeln(' Gender:     Female');

  writeln('---------------------------------------------------------------------');
  sleep(500);

  repeat
    writeln('Please enter your home phone number - no spaces please i.e. 01234567890');
    writeln;
    readln(tel);
  until (Length(tel) = 11) or (Length(tel) = 14);

  sleep(500);
  clrscr;
  writeln(' First Name: ', fname, '');
  writeln(' Surname:    ', sname, '');
  writeln(' Height:     ', Height: 0: 2, 'cm');
  writeln(' Salary:     ', chr(156), Salary: 0: 2);

  if upcase(gender) = 'M' then
    writeln(' Gender:     Male')
  else
    writeln(' Gender:     Female');

  writeln(' Telephone:  ', tel);
  writeln('---------------------------------------------------------------------');
  sleep(500);
  clrscr;
  writeln('Please enter your email address. It must contain an @ symbol and not contain:');
  writeln(' /');
  sleep(400);
  writeln(' <');
  sleep(400);
  writeln(' >');
  writeln(' \');
  sleep(400);
  writeln(' ,');
  sleep(400);
  writeln(' ;');
  readln(email);

  //Require a method to validate the email address.

  sleep(500);
  clrscr;
  writeln(' First Name: ', fname, '');
  writeln(' Surname:    ', sname, '');
  writeln(' Height:     ', Height: 0: 2, 'cm');
  writeln(' Salary:     ', chr(156), Salary: 0: 2);

  if upcase(gender) = 'M' then
    writeln(' Gender:     Male')
  else
    writeln(' Gender:     Female');

  writeln(' Telephone:  ', tel);
  writeln(' Email:      ', email);
  writeln('---------------------------------------------------------------------');
  sleep(500);

  writeln;
  writeln('Are you a vegetarian? Enter y/n (yes/no) ');
  writeln;
  readln(veg);
  sleep(500);
  clrscr;
  writeln(' First Name: ', fname, '');
  writeln(' Surname:    ', sname, '');
  writeln(' Height:     ', Height: 0: 2, 'cm');
  writeln(' Salary:     ', chr(156), Salary: 0: 2);


  if upcase(gender) = 'M' then
    writeln(' Gender:     Male')
  else
    writeln(' Gender:     Female');

  writeln(' Telephone:  ', tel);
  writeln(' Email:      ', email);

  if upcase(veg) = 'Y' then
    writeln(' Vegetarian: Yes')
  else
    writeln(' Vegetarian: No');

  writeln('---------------------------------------------------------------------');
  sleep(500);
  readln;

end.

Basically, you have to find if your string has one of the invalid characters and has one "@" symbol:

if (Pos('/', email) > 0) or (Pos('\', email) > 0) or (Pos('>', email) > 0) or (Pos('<', email) > 0) or (Pos(',', email) > 0) or (Pos(';', email) > 0) or (Pos('@', email) = 0)
then writeln('Invalid email address!');

the method above check if it is at least one "@" symbol. If you want to verify that in the email address contains exactly 1 "@" character, loop through the "email" string and count the appearances:

iCount :=0;
for i := 1 to Length(email) do 
    if email[i] = '@' then iCount := iCount + 1;
if iCount <> 1 then writeln('invalid email address');
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