In a textfile, How to express if ( Line 1's answer = Line 2's answer ) then - delphi

Question

I just started Delphi.
I'm making a simple login form, and the text file (UserInfo.txt) is set up like this
I just want Delphi to run through the TextFile to look for the string, then if that string equals edtUseranme.Text then it must check if that string is equal to the string on the second line.
If it equals then it can continue to the next Form
Here is my code:
for I := 0 to Eof(tFile) do
begin
Readln(tFile, sLine);
Inc(I);
if ReadLn(tFile) = edtUsername.Text then
begin
if edtUsername.Text = then
begin
frmMain.Show;
frmLogin.Hide;
end
else
begin
ShowMessage('INPUT INVALID (Try again)');
end;
end;
end;
At that second if statement, I don't know what to put after =.

Answer 1

Like Ken White suggested, you could redesign your text file and then use a TStringList to parse it. That would certainly make it easier to work with the data. However, if you want to stick with the code you already have, then you could do something more like this instead:
var
tFile: TextFile;
//Declare variables for temporally storing read username and password
sUser, sPass, sDivider: string;
Valid: Boolean;
...
Valid := False;
//use while loop to read every line till the end of file
while not Eof(tFile) do
begin
//Read username into sUser variable
Readln(tFile, sUser);
//Read password into sPass variable
Readln(tFile, sPass);
//Read divider into sDivider variable
Readln(tFile, sDivider);
//Use if clause to perform multiconditional logical comparison to see if
//read username and password equals to those specified in suitable edit
//boxes
//NOTE: Each separate logical condition must be in its own brackets
if (sUser = edtUsername.Text) and (sPass = edtPassword.Text) then
begin
//If conditions are met we set local variable Valid to true
Valid := True;
//and then break the loop
Break;
end;
end;
//If local variable valid was set to True show the main form
if Valid then
begin
frmMain.Show;
frmLogin.Hide;
end else
//else we show message about invalid input entered
ShowMessage('INPUT INVALID (Try again)');

Answer 2

Your file format is poorly designed for what you're wanting to do, I'm afraid.
You'd be better off using a more standard format (realizing, of course, that it's totally insecure to store names and passwords as plain text). Delphi makes it easy to work with name/value pairs using TStringList with text like this:
Name=Value
This would mean your text file would contain the username=password type lines:
Bob=Password
Sue=Bambi
You then use TStringList to load the file and read the value associated with the name, like this:
var
SL: TStringList;
UserName, Password: string;
begin
UserName := Edit1.Text; // Your username control
Password := Edit2.Text;
// You should check to make sure that both the username and password
// were entered here before proceeding. I'll leave that to you to do.
SL := TStringList.Create;
try
SL.LoadFromFile('C:\Temp\UserInfo.txt'); // Replace with your filename
// The next line looks for a name in the stringlist equal to the
// entered username, and if it's found compares its value to the
// password that was provided.
//
// You'll need to handle making sure that you do a case-sensitive
// (or non-sensitive, depending on your needs) comparison is done
// if needed.
if SL.Values[UserName] = Password then
// Login succeeded
else
// Login failed.
finally
SL.Free;
end;
end;