when enter text in textbox. that text count is display in label?

Question

hi! sir
i place one textbox and label. i take textboxbox properties is multiline:True and Maxlength:150
and bottom of the text i take lable. and label text is 150. (Characters Left: 150)
my aim is when i enter text in text box , in the label value is decreased. and cut,paste,delete operations are also performed.
means if i cut the text that time label value is increase and if i paste the text label value is decrease.
if label value is reach '0' if i  try to enter text in textbox, text is not entered.
plrase give a code for this.(This is web application)
one doubt i set maxlength is 150 to the textbox control and take multiline is true. if i reach 150 characters and type text also it is print.
why print the text in textbox i reach the maxlength?
please give a solution.
Thanks.