how can we give case sensitive for user login text and data base value in C# .net windows form application

Using collations
eg:

if ('a'='A' Collate Latin1_General_CI_AI) 
    print'same 1'
else
    print 'different 1'

if ('a'='A' Collate Latin1_General_CS_AI) 
    print'same 2'
else
    print 'different 2' 

The CS in the collation name indicates Case Sensitive (and CI, Case Insensitive). The AI/AS relates to accent sensitivity.

And If you want to check in C# code then you can Use

IsUpper()

Or

IsLower()

Methods.