app crashing when ever i entering negitive value

I am working on a requirement, where i have two text fields when i enter a Celsius value in first text field automatically it converts into Fahrenheit

The problem i'm facing is when ever i entering a negative value app is crashing

Here is my code

My XML file

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://ift.tt/nIICcg"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
android:padding="20dp" >

<TextView
    android:id="@+id/textView1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Celsius" />

<EditText
    android:id="@+id/myTextBox"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:inputType="numberSigned" />

<TextView
    android:id="@+id/textView2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Forenheight" />

<EditText
    android:id="@+id/outputBox"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:inputType="numberSigned" />

<TextView
    android:id="@+id/tv_in_for"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Forenheit" />

<EditText
    android:id="@+id/et_in_for"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:inputType="numberSigned" />

<TextView
    android:id="@+id/tv_out_cel"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Celsius" />

<EditText
    android:id="@+id/et_out_cel"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:inputType="numberSigned" />

</LinearLayout>

This is my java code

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.type2);
    final EditText outputTextBox = (EditText) findViewById(R.id.outputBox);
    final EditText myTextBox = (EditText) findViewById(R.id.myTextBox);
    myTextBox.addTextChangedListener(new TextWatcher() {

        public void afterTextChanged(Editable s) {
        }

        public void beforeTextChanged(CharSequence s, int start, int count,
                int after) {
        }

        public void onTextChanged(CharSequence s, int start, int before,
                int count) {

            String inputs = myTextBox.getText().toString();
            if (TextUtils.isEmpty(inputs)) {
                outputTextBox.setText("0");
            } else {
                float i = Float.parseFloat(inputs);
                i= ((i * 9) / 5) + 32;
                outputTextBox.setText(String.valueOf(i));
            }
        }
    });

    final EditText in_for = (EditText) findViewById(R.id.et_in_for);
    final EditText out_cel = (EditText) findViewById(R.id.et_out_cel);
    in_for.addTextChangedListener(new TextWatcher() {

        @Override
        public void onTextChanged(CharSequence s, int start, int before, int count) {
            // TODO Auto-generated method stub

        }

        @Override
        public void beforeTextChanged(CharSequence s, int start, int count,
                int after) {
            // TODO Auto-generated method stub

        }

        @Override
        public void afterTextChanged(Editable s) {
            // TODO Auto-generated method stub
            String inputs = in_for.getText().toString();
            if (TextUtils.isEmpty(inputs)) {
                in_for.setText("0");
            } else {
                float i = Float.parseFloat(inputs);
                i= ((i - 32) * 5 / 9);
                out_cel.setText(String.valueOf(i));
            }
        }
    });
}

please Help me out in this.