Precise calculations in Android development, Java?

Question

I'm creating a calculator for Android, Well so far it looks pretty much done... The thing is the answers are not precise, Addition, subtraction, multiplication work fine as decimal is usually not required.. When it comes to division the answer is rounded to the nearest integer rather than showing the answer in decimal... So i changed the TextView type to show decimals and used float instead of int for the variable containing the answer. The result is I end up with a rounded integer with a ".00" in the ending :/ Please help! My code : MainActivity.java :

package in.rohanbojja.basiccalculator;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.EditText;
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 add( View view){

        EditText n1 = (EditText) findViewById(R.id.editText1);
        EditText n2 = (EditText) findViewById(R.id.editText3);
        TextView res = (TextView) findViewById(R.id.textView1);

        String sn1 = n1.getText().toString();
        String sn2 = n2.getText().toString();
        String sres;

        int in1 = Integer.parseInt(sn1);
        int in2 = Integer.parseInt(sn2);
        float ires;

        ires = in1 + in2;
        sres = Float.toString(ires);
        res.setText(sres);
}
public void sub( View view ){

    EditText n1 = (EditText) findViewById(R.id.editText1);
    EditText n2 = (EditText) findViewById(R.id.editText3);
    TextView res = (TextView) findViewById(R.id.textView1);

    String sn1 = n1.getText().toString();
    String sn2 = n2.getText().toString();
    String sres;

    int in1 = Integer.parseInt(sn1);
    int in2 = Integer.parseInt(sn2);
    float ires;

    ires = in1 - in2;
    sres = Float.toString(ires);
    res.setText(sres);
}
public void mul( View view ){

    EditText n1 = (EditText) findViewById(R.id.editText1);
    EditText n2 = (EditText) findViewById(R.id.editText3);
    TextView res = (TextView) findViewById(R.id.textView1);

    String sn1 = n1.getText().toString();
    String sn2 = n2.getText().toString();
    String sres;

    int in1 = Integer.parseInt(sn1);
    int in2 = Integer.parseInt(sn2);
    float ires;

    ires = in1 * in2;
    sres = Float.toString(ires);
    res.setText(sres);

}


public void clr( View view ){

    EditText n1 = (EditText) findViewById(R.id.editText1);
    EditText n2 = (EditText) findViewById(R.id.editText3);
    TextView res = (TextView) findViewById(R.id.textView1);

    n1.setText("");
    n2.setText("");
    res.setText("Result");
}

public void div( View view){
    EditText n1 = (EditText) findViewById(R.id.editText1);
    EditText n2 = (EditText) findViewById(R.id.editText3);
    TextView res = (TextView) findViewById(R.id.textView1);

    String sn1 = n1.getText().toString();
    String sn2 = n2.getText().toString();
    String sres;

    int in1 = Integer.parseInt(sn1);
    int in2 = Integer.parseInt(sn2);
    float ires;

    ires = in1/in2;
    sres = Float.toString(ires);
    res.setText(sres);
}
}

You need to do some reading on number types and math in Java in general. — kabuko, Apr 11 '13 at 19:51

score 6 · Answer 1 · answered Apr 11 '13 at 19:51

6

int in1 = Integer.parseInt(sn1);
int in2 = Integer.parseInt(sn2);
float ires;

ires = in1/in2;

You are still doing integer division, you're just storing the result in a float. To perform floating point division, in1 and in2 must be floats.

answered Apr 11 '13 at 19:51

Aurand

5,487
1
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Not exactly. in2 needs to be a float or double, but in1 is not required. – Igor Rodriguez Apr 11 '13 at 19:52
1

True. I simplified for the benefit of the OP. – Aurand Apr 11 '13 at 19:53

score 4 · Accepted Answer · answered Apr 11 '13 at 19:53

I see that you have tried to force a floating-point result by storing the result in a float, but unfortunately this won't do it. Operators in Java, such as the division operator (/) work like this:

If BOTH operands are floats, the result is a float.
If ONE of the operands is a float, the result is a float.
If NEITHER of the operands are floats (i.e. they are both integers), the result is an int.

Since yours falls into the latter case, you get an integer result. The solution is to force one of your operands to be a float, not just the resulting variable, like so:

ires = ((float) in1) / in2;

score 0 · Answer 3 · answered Apr 11 '13 at 19:51

0

In div : in1 and in2 are ints. You need to parse sn1 and sn2 as Floats.

answered Apr 11 '13 at 19:51

vptheron

7,426
25
34

score 0 · Answer 4 · answered Apr 11 '13 at 19:51

0

your have some little mistake, you should conver in1 and in2 to float, or something like this:

ires = (float)in1/in2;

answered Apr 11 '13 at 19:51

Farnabaz

4,030
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Precise calculations in Android development, Java?

4 Answers4