修复小学题目计算精度问题：先精确计算再保留小数

src/com/mathlearning/model/BaseQuestionGenerator.java

@@ -36,6 +36,7 @@ public abstract class BaseQuestionGenerator {
         return !(answer < 0 || Double.isNaN(answer) || Double.isInfinite(answer));
     }
 
+    // 修改：使用double进行精确计算，只在最后保留小数
     protected double calculateExpression(double[] values, int[] operations) {
         List<Double> numbers = new ArrayList<>();
         List<Integer> ops = new ArrayList<>();
@@ -94,6 +95,7 @@ public abstract class BaseQuestionGenerator {
             result = performOperation(result, nextNum, op);
         }
 
+        // 修改：只在最后一步进行四舍五入保留2位小数
         return Math.round(result * 100) / 100.0;
     }
 
@@ -104,6 +106,7 @@ public abstract class BaseQuestionGenerator {
             case 2: return left * right;
             case 3:
                 if (right == 0) return Double.NaN;
+                // 修改：直接进行除法，不在这里保留小数
                 return left / right;
             default: return left;
         }
@@ -113,8 +116,9 @@ public abstract class BaseQuestionGenerator {
         String[] options = new String[4];
         Set<String> usedValues = new HashSet<>();
 
-        boolean isIntegerAnswer = (answer == (int) answer);
-        String correctAnswer = formatAnswer(answer);
+        // 修改：判断是否为整数的逻辑
+        boolean isIntegerAnswer = Math.abs(answer - Math.round(answer)) < 1e-10;
+        String correctAnswer = formatAnswer(answer, isIntegerAnswer);
 
         options[0] = correctAnswer;
         usedValues.add(correctAnswer);
@@ -134,7 +138,8 @@ public abstract class BaseQuestionGenerator {
 
             do {
                 double wrongValue = generateWrongValue(answer, isIntegerAnswer);
-                wrongAnswer = formatAnswer(wrongValue);
+                wrongAnswer = formatAnswer(wrongValue,
+                        Math.abs(wrongValue - Math.round(wrongValue)) < 1e-10);
                 attempts++;
             } while (usedValues.contains(wrongAnswer) && attempts < 20);
 
@@ -147,20 +152,26 @@ public abstract class BaseQuestionGenerator {
         double offset = (random.nextDouble() * 5) + 1;
 
         if (isIntegerAnswer) {
-            int intAnswer = (int) answer;
+            int intAnswer = (int) Math.round(answer);
             int intOffset = random.nextInt(10) + 1;
             double wrongValue = random.nextBoolean() ?
                     intAnswer + intOffset : Math.max(1, intAnswer - intOffset);
-            return (int) wrongValue;
+            return wrongValue;
         } else {
             double wrongValue = random.nextBoolean() ? answer + offset : answer - offset;
+            // 修改：错误选项也保留2位小数
             return Math.round(wrongValue * 100) / 100.0;
         }
     }
 
-    private String formatAnswer(double answer) {
-        return (answer == (int) answer) ?
-                String.valueOf((int) answer) : String.format("%.2f", answer);
+    // 修改：格式化答案，只在最后一步处理小数位数
+    private String formatAnswer(double answer, boolean isInteger) {
+        if (isInteger) {
+            return String.valueOf((int) Math.round(answer));
+        } else {
+            // 确保显示2位小数，即使末尾是0
+            return String.format("%.2f", answer);
+        }
     }
 
     private void shuffleArray(String[] array) {