How to do a validation of authorized users using a loop?

Question

C++ / C#

Write a code to verify that a username and password are entered, which you then need to check with already registered users. If there is a match, then "login completed successfully", otherwise "Login failed! Invalid username or password!"

Answer 1

And what about the cycle? Usually, logins and passwords (more precisely, their hashes) are stored in the database. When entering a login / password, the presence of such a user in the database is checked (by SQL query) and if there is one, then the hash of the entered password is compared with the hash in the database.