function call during onclick of button in page

function call during onclick of button in page

Hi,


<button class="w3-btn w3-round-large w3-black w3-xlarge" style="width:500px;margin:5px 130px 5px 130px;"><a class="zc-formbutton" href=<%=thisapp.sendMailAccept(idnum)%> style="background-color:#000000"><font face="Arial, Helvetica, sans-serif" size="3 px" color="#FFFEFE">I fully understood the terms & conditions.</font></a></button>
 



I am getting an issue while executing the above code.

This code instead of executed during onclick of button , it is getting executed during onload of the page.

Please let me know the solution. to call function during the onclick of the button

Thanks 
ITKES