Whenever I try to press a radio button on my emulator, it just force closes!

public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        Button b = (Button)this.findViewById(R.id.btn_confirm);
        b.setOnClickListener(this);
        RadioButton radio_ctf = (RadioButton) findViewById(R.id.radio_ctf);
        RadioButton radio_ftc = (RadioButton) findViewById(R.id.radio_ftc);
        radio_ctf.setOnClickListener(this);
        radio_ftc.setOnClickListener(this);
    }
    @Override
    public void onClick(View v)
    {
     TextView tv = (TextView)this.findViewById(R.id.tv_result);
     EditText et = (EditText)this.findViewById(R.id.et_name);
     RadioButton radio_ctf = (RadioButton) findViewById(R.id.radio_ctf);
        RadioButton radio_ftc = (RadioButton) findViewById(R.id.radio_ftc);
     double y = 0;
     int x = Integer.parseInt(et.getText().toString());
     if(radio_ctf.isChecked())
     {
      y = ((double)x * 1.8) + 32;
     }
     if(radio_ftc.isChecked())
     {
      y = ((double)x - 32) * 0.555;
     }
     String text = "Result:" + y;
     tv.setText(text);