:v

3.  import android.os.Bundle;
 import android.app.Activity;
 import android.view.Menu;
 import android.view.View;
 import android.widget.EditText;
 import android.widget.RadioButton;
 import android.widget.TextView;

 public class MainActivity extends Activity {
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 }
 @Override
 public boolean onCreateOptionsMenu(Menu menu) {
 // Inflate the menu; this adds items to the action bar if it is present.
 getMenuInflater().inflate(R.menu.main, menu);
 return true;
 }

 public void operar(View view) {

4.  if(radio0.isChecked()==true){
 int suma=nro1+nro2;
 String resultado=String.valueOf(suma);
 tv3.setText(resultado);
 }else
 if(radio1.isChecked()==true){
 int resta=nro1-nro2;
 String resultado=String.valueOf(resta);
 tv3.setText(resultado);
 }
 }
 }