From 83e92859aa10f20b9b42053516a1fe667e12e5c6 Mon Sep 17 00:00:00 2001
From: NorbiPeti <szatmari.norbert.peter@gmail.com>
Date: Wed, 20 Jul 2016 09:55:24 +0200
Subject: [PATCH] Improved error messages

---
 src/calculator/Calc.java | 12 ++++--------
 src/calculator/Gui.java  | 19 +++++++++++++------
 2 files changed, 17 insertions(+), 14 deletions(-)

diff --git a/src/calculator/Calc.java b/src/calculator/Calc.java
index abbeff0..ea4c4ad 100644
--- a/src/calculator/Calc.java
+++ b/src/calculator/Calc.java
@@ -14,18 +14,14 @@ public class Calc {
 
 	private static final Pattern PARENTHESIS = Pattern.compile("\\(([^()]+)\\)");
 
-	public static Double calculate(String text) {
+	public static String calculate(String text) {
 		StringBuffer buf = new StringBuffer(text);
 		replace(buf, PARENTHESIS, (a) -> calculate(a));
 		replace(buf, MULTIPLY, (a, b) -> a * b);
 		replace(buf, DIVIDE, (a, b) -> a / b);
 		replace(buf, ADD, (a, b) -> a + b);
 		replace(buf, SUBTRACT, (a, b) -> a - b);
-		try {
-			return Double.parseDouble(buf.toString());
-		} catch (Exception e) {
-			return null;
-		}
+		return buf.toString();
 	}
 
 	private static void replace(StringBuffer buf, Pattern pattern, BiFunction<Double, Double, Double> doit) {
@@ -38,12 +34,12 @@ public class Calc {
 		}
 	}
 
-	private static void replace(StringBuffer buf, Pattern pattern, Function<String, Double> doit) {
+	private static void replace(StringBuffer buf, Pattern pattern, Function<String, String> doit) {
 		while (true) {
 			Matcher matcher = pattern.matcher(buf.toString());
 			if (!matcher.find())
 				break;
-			buf.replace(matcher.start(), matcher.end(), Double.toString(doit.apply(matcher.group(1))));
+			buf.replace(matcher.start(), matcher.end(), doit.apply(matcher.group(1)));
 		}
 	}
 }
diff --git a/src/calculator/Gui.java b/src/calculator/Gui.java
index 93b2119..c4af8b0 100644
--- a/src/calculator/Gui.java
+++ b/src/calculator/Gui.java
@@ -118,13 +118,20 @@ public class Gui {
 				tf.setText("0.0");
 				return;
 			}
-			Double ret = Calc.calculate(tf.getText());
-			if (ret == null)
-				JOptionPane.showMessageDialog(frame,
-						"Unable to convert result to number!\nThis is usually caused by a mistype, like \"5++5\"",
-						"Error!", JOptionPane.WARNING_MESSAGE);
+			String result = Calc.calculate(tf.getText());
+			String errormsg = "Unbalanced parenthesis: ";
+			int openc = result.length() - result.replace("(", "").length();
+			int closec = result.length() - result.replace(")", "").length();
+			if (openc - closec > 0)
+				errormsg += "There is " + (openc - closec) + " more of ( than )";
+			else if (openc - closec < 0) {
+				errormsg += "There is " + (closec - openc) + " more of ) than (";
+			} else
+				errormsg = "";
+			if (errormsg.length() == 0)
+				tf.setText(Double.toString(Double.parseDouble(result)));
 			else
-				tf.setText(Double.toString(ret));
+				JOptionPane.showMessageDialog(frame, errormsg, "Error!", JOptionPane.WARNING_MESSAGE);
 		} catch (ArithmeticException e) {
 			JOptionPane.showMessageDialog(frame, "Arithmetic error: " + e.getMessage(), "Error!",
 					JOptionPane.WARNING_MESSAGE);