initialize my label

hello my firends
i have a web page with a label,a button, a textbbox and a  drowpDown .I assign 1 to my lbl control in html code. i want to when i click on my drowpown show selectedvalue in my lbl then when i ckick on button show my lbl value in my textbox. I write bellow  code but when i click on my button my label's value return to that value that i assigned in html code.what 's the problem exactly ? and what is wrong in my code?
plz help me.
page_load(){}
drowpDown_selectedIndexChange(){   lbl.text=drowpdown.selectedValue  ;   }
button_click(){textbox1.Text=lbl.Text}