Login from txt file with attempt limits - c++

Question

i'm totally new to C++ and this forum. I tried searching the codes and found a piece of code but it doesn't work as what I wanted. I want a login that check every line of the txt file and grant access to the system if the username and password is correct.
string line = " ";
ifstream readfile("Login.txt");
string username, password, adminname, adminpass;
cout << "\nEnter Username: ";
cin >> username;
cout << "\nEnter Password: ";
cin >> password;
while (getline(readfile, line))
{
stringstream iss(line);
iss >> adminname >> adminpass;
//Login Success Function
if (username == adminname && password == adminpass)
{
cout << "\nLOGIN SUCCESSFUL!";
}
}
//Login Fail Function
{
int fail = 5;
while (fail > 0)
{
cout << "Error! Invalid Username and Password. Please reenter.\n";
cout << "You have " << fail << " tries left.\n";
cout << "\nEnter Username: ";
cin >> username;
cout << "\nEnter Password: ";
cin >> password;
fail--;
}
cout << "\nACCESS DENIED!";
}
The txt file consists of 1st line (admin123 password123), 2nd line (admin admin).
The login worked fine if I entered correctly however, if I enter wrong username or password I just stuck in the while loop until it shows access denied even if I enter correct username and password for the second try.
Can anyone help me to fix this? If possible please include the comments(the //) so that I am able to learn from it. Thanks in advance.

Answer 1

Since you mention in the comments that this is an assignment, I'm going to keep this pretty general.
In your program, you prompt once for username and password, then read through the file to see if there is a match.
If there is no match, you then prompt for username and password again in a loop, but do not check to see if they are valid. This is what the problem is. Each time you get a new username and password, check to see if they are valid.
There are (at least) two possible approaches:
Include the "fail" and re-prompt logic around the code that reads the file. So you get a username and password, then read the file checking for a match. If no match, do it again. In this case, you would be reading the file each time. For a large data-set, this could get slow. For this problem, it should be fine.
Read the file once and save the values (Have you studied arrays, vectors, or other data structures? You need at least some of those things to do this). I would use a std::map here because it is direct access and would be the smallest amount of code, but there are many other ways to do this as well.
Here is a possible way to do it with re-reading the file. Note that this mostly just re-organizing the code you already have:
bool success = false; //use this as part of our loop condition
int fail = 5;
while (!success && fail > 0) //loop until we succeed or failed too much
{
//get the username and password
cout << "\nEnter Username: ";
cin >> username;
cout << "\nEnter Password: ";
cin >> password;
//open the file and see if we have a match
ifstream readfile("Login.txt");
while (getline(readfile, line))
{
stringstream iss(line);
iss >> adminname >> adminpass;
//Login Success Function
if (username == adminname && password == adminpass)
{
//we have a match, so set success to true so we exit the loop
success = true;
}
}
if (!success) //we did not find a match in the file
{
//so we output the message
cout << "Error! Invalid Username and Password. Please reenter.\n";
cout << "You have " << fail << " tries left.\n";
fail--;
}
}
//now we know if we had success or not, so report it
if (success)
{
cout << "\nLOGIN SUCCESSFUL!";
}
else
{
cout << "\nACCESS DENIED!";
}