Handle errors: division by 0, tan, logarithms, square root

Author: gruszm

app/src/main/java/com/example/kalkulator/activities/AdvancedCalculatorActivity.java

@@ -5,6 +5,7 @@
 import android.os.Vibrator;
 import android.view.View;
 import android.widget.Button;
+import android.widget.Toast;
 import androidx.appcompat.app.AppCompatActivity;
 import com.example.kalkulator.R;
 import com.example.kalkulator.listeners.DigitOnClickListener;
@@ -128,7 +129,11 @@ public void percentOnClick(View v)
 
             String formattedOutput = DECIMAL_FORMAT.format(result).replace('.', ',');
 
-            if (!isOutputTooLong(formattedOutput))
+            if (formattedOutput.equals(INFINITY_SYMBOL))
+            {
+                Toast.makeText(this, "Cannot divide by 0", Toast.LENGTH_SHORT).show();
+            }
+            else if (!isOutputTooLong(formattedOutput))
             {
                 prevValueTextView.setText("");
                 operationTextView.setText("");
@@ -147,9 +152,16 @@ private void logOnClick(View view)
 
         Double currValue = Double.parseDouble(valueText.replace(',', '.'));
 
-        currValue = Math.log10(currValue);
+        if (currValue > 0.0D)
+        {
+            currValue = Math.log10(currValue);
 
-        valueTextView.setText(DECIMAL_FORMAT.format(currValue).replace('.', ','));
+            valueTextView.setText(DECIMAL_FORMAT.format(currValue).replace('.', ','));
+        }
+        else
+        {
+            Toast.makeText(this, "The number must not be negative", Toast.LENGTH_SHORT).show();
+        }
 
         makeStandardVibration();
     }
@@ -160,9 +172,16 @@ private void sqrtOnClick(View view)
 
         Double currValue = Double.parseDouble(valueText.replace(',', '.'));
 
-        currValue = Math.sqrt(currValue);
+        if (currValue >= 0.0D)
+        {
+            currValue = Math.sqrt(currValue);
 
-        valueTextView.setText(DECIMAL_FORMAT.format(currValue).replace('.', ','));
+            valueTextView.setText(DECIMAL_FORMAT.format(currValue).replace('.', ','));
+        }
+        else
+        {
+            Toast.makeText(this, "The number must not be negative", Toast.LENGTH_SHORT).show();
+        }
 
         makeStandardVibration();
     }
@@ -173,9 +192,16 @@ private void lnOnClick(View view)
 
         Double currValue = Double.parseDouble(valueText.replace(',', '.'));
 
-        currValue = Math.log(currValue);
+        if (currValue > 0.0D)
+        {
+            currValue = Math.log(currValue);
 
-        valueTextView.setText(DECIMAL_FORMAT.format(currValue).replace('.', ','));
+            valueTextView.setText(DECIMAL_FORMAT.format(currValue).replace('.', ','));
+        }
+        else
+        {
+            Toast.makeText(this, "The number must not be negative", Toast.LENGTH_SHORT).show();
+        }
 
         makeStandardVibration();
     }
@@ -211,10 +237,25 @@ private void tanOnClick(View view)
         String valueText = valueTextView.getText().toString();
 
         Double currValue = Double.parseDouble(valueText.replace(',', '.'));
+        double delta = 1E-3;
 
-        currValue = Math.tan(currValue);
+        // find k
+        int k = (int) Math.round((currValue - Math.PI / 2) / Math.PI);
 
-        valueTextView.setText(DECIMAL_FORMAT.format(currValue).replace('.', ','));
+        // calculate the difference
+        double diff = Math.abs(currValue - (Math.PI / 2 + k * Math.PI));
+
+        // check if the input is very close to PI/2 + kPI
+        if (diff < delta)
+        {
+            Toast.makeText(this, "The input is very close or equal to PI/2 + kPI, so the result does not exist", Toast.LENGTH_LONG).show();
+        }
+        else
+        {
+            currValue = Math.tan(currValue);
+
+            valueTextView.setText(DECIMAL_FORMAT.format(currValue).replace('.', ','));
+        }
 
         makeStandardVibration();
     }
@@ -292,7 +333,11 @@ public void equalsOnClick(View v)
 
             String formattedOutput = DECIMAL_FORMAT.format(result).replace('.', ',');
 
-            if (!isOutputTooLong(formattedOutput))
+            if (formattedOutput.equals(INFINITY_SYMBOL))
+            {
+                Toast.makeText(this, "Cannot divide by 0", Toast.LENGTH_SHORT).show();
+            }
+            else if (!isOutputTooLong(formattedOutput))
             {
                 prevValueTextView.setText("");
                 operationTextView.setText("");

app/src/main/java/com/example/kalkulator/activities/SimpleCalculatorActivity.java

@@ -5,6 +5,7 @@
 import android.os.Vibrator;
 import android.view.View;
 import android.widget.Button;
+import android.widget.Toast;
 import androidx.appcompat.app.AppCompatActivity;
 import com.example.kalkulator.R;
 import com.example.kalkulator.listeners.DigitOnClickListener;
@@ -148,7 +149,11 @@ public void equalsOnClick(View v)
 
             String formattedOutput = DECIMAL_FORMAT.format(result).replace('.', ',');
 
-            if (!isOutputTooLong(formattedOutput))
+            if (formattedOutput.equals(INFINITY_SYMBOL))
+            {
+                Toast.makeText(this, "Cannot divide by 0", Toast.LENGTH_SHORT).show();
+            }
+            else if (!isOutputTooLong(formattedOutput))
             {
                 prevValueTextView.setText("");
                 operationTextView.setText("");

app/src/main/java/com/example/kalkulator/utils/CalculatorHandler.java

@@ -15,6 +15,7 @@ public class CalculatorHandler
     public static final char CHAR_MULTIPLY = '⨯';
     public static final char CHAR_DIVIDE = '÷';
     public static final char CHAR_POWER = '^';
+    public static final String INFINITY_SYMBOL = "\u221E"; // infinity symbol (dividing by zero)
     public static final int VALUE_TEXT_VIEW_MAX_SIZE = 10;
     public static final int OUTPUT_MAX_SIZE = 20;
     public static final DecimalFormat DECIMAL_FORMAT = new DecimalFormat("#.##########");