How to check the string entries in vs with database

Question

Hi friends

I have a user table that contains username and password and other properties

For example in the database I have username = JOHN and password = 1234JOHN

When i input in visual studio

Username = john and password = 1234joHn

C # accepts this does not return an error

I hope that I have described my problem well and I will be happy if someone helps me to solve this problem

thank you in advance