请问这段程序有问题吗?运行后说运行期错误
<%@ Language=VBScript %>
<%
sub show()
username.value=""
end sub
sub clearall()
username.value=""
end sub
%>
<html>
<body>
<input name="username" maxlength="20" class="textbox" size="20" style="font-size: 10pt">
<br>
<INPUT onclick=vbscript:show() type=submit value="登陆">
<INPUT onclick=vbscript:clearall() type=submit value="清除">
</body>
</html>