to close a application

Question

hi friends.. my query is in windows apllication.. i enter a particular text into textbox first time during run time it will give a warning message... ex.textbox1.text=hi second time i enter the same text to that textbox (hi)means it will give a message and the system will be logoff ( if i enter the same text during second time...) i need coding for that in vb or c#.. regards gopal