for build calculate and make errors : <p>in my project for build calculate has error like this :</p>

<pre><code>void findView(){

        btn_0=(Button)findViewById(R.id.btn_0);
           btn_1=(Button)findViewById(R.id.btn_1);
</code></pre>

<p>and cannot resolve symbol for anythings have R ,what should i do ?</p>
