CODEWITHSUNDEEP
javaandroidmath
PHaZerous
PHaZerous

Reputation: 59

Why are my Java percentages slightly wrong?

I'm writing a simple Percentage Calculator android app in Android Studio. Here's my psuedo:

    resultView = (TextView) findViewById(R.id.ResultView);
    percentageText = (EditText) findViewById(R.id.PercentageInput);
    numberText = (EditText) findViewById(R.id.NumberInput);

    Button calcButton = (Button) findViewById(R.id.Calculate_btn);
    calcButton.setOnClickListener(new View.OnClickListener() {
         @Override
         public void onClick(View view)
         {
             if(percentageText.length() != 0 && numberText.length() != 0)
             {
                 float percentage = Float.parseFloat(percentageText.getText().toString()) / 100;
                 float result = percentage * Float.parseFloat(numberText.getText().toString());
                 resultView.setText(Float.toString(result));
             }
             else if(percentageText.length() == 0 && numberText.length() == 0)
             {
                 resultView.setText("Don't be dumb...");
             }
         }
      });

so it seemed like everything was working fine. Simple percentages are always right. 50%100=50, 25%50=12.5 ... but then I get to 3 and 6. 3%10= 0.29999998 ... shouldn't it be .3? and 60%100= 60.000004 ... Any help out there?

Upvotes: 1

Views: 92

Answers (1)

Maljam
Maljam

Reputation: 6274

It has to do with the fact that double variables have a limited number of bits. This is like saying 1/3 = 0.33333333 when really is should be equal to 0.33333333... forever!

Read about Floating points and Double precision

Upvotes: 4

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