How to write a complex average equation in android?

Question

Just replace the [] and {} with () in the equation, you can only use () because [] and {} have special meaning in Java.

EDIT 1:

The logcat output tells you pretty much exactly what the problem is:

java.lang.ArithmeticException: divide by zero

You are diving by zero and since the only variable you are diving by is numarValori and numarValori2 one of these has to be 0.

What I think is happening is this: When You click the calculate button you are performing both calculations. When nothing has been entered for the second calculation every input variable defaults back to 0 and when all variables are 0 so is numarValori2. When the calculation is then performed it will divide by zero.

I can suggest a few changes to your code to improve it, give me a few minutes and I will edit my answer.

EDIT 2:

Here is my improved source code. I didn't test it (I will if I find the time in about half an hour) but it should work:

import android.app.Activity;
import android.os.Bundle;
import android.text.Editable;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class Medii extends Activity {

    private EditText txtNum1;
    private EditText txtNum2;
    private EditText txtNum3;
    private EditText txtNum4;
    private EditText txtNum5;
    private EditText txtNum6;
    private EditText txtNum7;
    private EditText txtNum8;
    private EditText txtTotal;
    private EditText txtNum10;
    private EditText txtNum11;
    private EditText txtNum12;
    private EditText txtNum13;
    private EditText txtNum14;
    private EditText txtNum15;
    private EditText txtNum16;
    private EditText txtNum17;
    private EditText txtNum18;
    private EditText txtNum19;
    private EditText txtNum20;
    private EditText txtTotal2;
    private Button btnCal;
    private Button btnCal2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.medii);

        txtNum1 = (EditText) findViewById(R.id.editText1);
        txtNum2 = (EditText) findViewById(R.id.editText2);
        txtNum3 = (EditText) findViewById(R.id.editText3);
        txtNum4 = (EditText) findViewById(R.id.editText4);
        txtNum5 = (EditText) findViewById(R.id.editText5);
        txtNum6 = (EditText) findViewById(R.id.editText6);
        txtNum7 = (EditText) findViewById(R.id.editText7);
        txtNum8 = (EditText) findViewById(R.id.editText8);
        txtTotal = (EditText) findViewById(R.id.editText9);
        btnCal = (Button) findViewById(R.id.bmedii);
        txtNum10 = (EditText) findViewById(R.id.editText10);
        txtNum11 = (EditText) findViewById(R.id.editText11);
        txtNum12 = (EditText) findViewById(R.id.editText12);
        txtNum13 = (EditText) findViewById(R.id.editText13);
        txtNum14 = (EditText) findViewById(R.id.editText14);
        txtNum15 = (EditText) findViewById(R.id.editText15);
        txtNum16 = (EditText) findViewById(R.id.editText16);
        txtNum17 = (EditText) findViewById(R.id.editText17);
        txtNum18 = (EditText) findViewById(R.id.editText18);
        txtNum19 = (EditText) findViewById(R.id.editText19);
        txtTotal2 = (EditText) findViewById(R.id.editText20);
        btnCal2 = (Button) findViewById(R.id.bmedii12);

        btnCal.setOnClickListener(new SimpleAverageClickListener());
        btnCal2.setOnClickListener(new ComplexAverageClickListener());

    }

    private double getNumberFromEditText(EditText editText, double defaultValue) throws NumberFormatException {
        if (editText != null) {
            Editable editable = editText.getText();
            if (editable != null) {
                return Double.parseDouble(editable.toString());
            }
        }
        return defaultValue;
    }

    private boolean isEditTextEmpty(EditText editText) {
        if (editText != null) {
            Editable editable = editText.getText();
            if (editable != null) {
                return editable.toString().isEmpty();
            }

        }
        return true;
    }

    private double getAverageOfEditTexts(EditText... editTexts) throws NumberFormatException{
        double divider = 0.0;
        double sum = 0.0;
        for (EditText editText : editTexts) {
            if (!isEditTextEmpty(editText)) {
                divider++;
                sum += getNumberFromEditText(editText, 0.0);
            }
        }
        return sum / divider;
    }


    private class SimpleAverageClickListener implements Button.OnClickListener {

        @Override
        public void onClick(View v) {

            try {
                double average = getAverageOfEditTexts(txtNum1, txtNum2, txtNum3, txtNum4, txtNum5, txtNum6, txtNum7, txtNum8);
                txtTotal.setText(String.valueOf(average));
            } catch (NumberFormatException e) {
                // Exception occurred because of illegal input, do nothing.
            }
        }
    }

    private class ComplexAverageClickListener implements Button.OnClickListener {

        @Override
        public void onClick(View v) {

            try {
                double average = getAverageOfEditTexts(txtNum10, txtNum11, txtNum12, txtNum13, txtNum14, txtNum15, txtNum16, txtNum17, txtNum18);
                double total = (average * 3 + getNumberFromEditText(txtNum19, 0.0)) / 4.0;
                txtTotal2.setText(String.valueOf(total));
            } catch (NumberFormatException e) {
                // Exception occurred because of illegal input, do nothing.
            }
        }
    }
}