.net - Combo Box Drop down list to change a variable -

i creating program drop down-list combo box contain items: a,b,cand d.

what want is, when select item in combobox , click button, x variable change. example when select b in combobox, x value change 2.

i need variable function. how can change x variable?

if combobox1.selecteditem.tostring = "a"     x = 1 elseif combobox1.selecteditem.tostring = "b"     x = 2 elseif combobox1.selecteditem.tostring = "c"     x = 3 elseif combobox1.selecteditem.tostring = "d"     x = 4 end if 

assuming x integer