@Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.second); setTitle("Second Activity"); Intent inIntent = getIntent(); String calc = inIntent.getStringExtra("calc"); final double first = inIntent.getDoubleExtra("first", 0); final double second = inIntent.getDoubleExtra("second", 0); final double result; Button ret = (Button) findViewById(R.id.ret); if (calc.equals("plus")) result = Double.parseDouble(String.format("%.3f", first + second)); else if (calc.equals("minus")) result = Double.parseDouble(String.format("%.3f", first - second)); else if (calc.equals("multiply")) result = Double.parseDouble(String.format("%.3f", first * second)); else if (calc.equals("divider")) result = Double.parseDouble(String.format("%.3f", first / second)); else result = 0; ret.setOnClickListener( new View.OnClickListener() { @Override public void onClick(View v) { Intent outIntent = new Intent(getApplicationContext(), MainActivity.class); outIntent.putExtra("result", result); setResult(RESULT_OK, outIntent); finish(); } }); }