🐛 Fix case like y=80%*x painting wrongly

lib/parser.dart

@@ -43,22 +43,26 @@ class Parser {
   Expr parseMul() {
     var expr = parsePow();
     skipSpaces();
-    while (!isEnd && (current == '*' || current == '/')) {
+    while (!isEnd &&
+        (current == '*' ||
+            current == '/' ||
+            current == '%' ||
+            RegExp(r'[a-zA-Z\d]').hasMatch(current) ||
+            current == '(')) {
+      if (current == '*' || current == '/') {
         var op = current;
         eat();
         var right = parsePow();
-      if (op == '*') {
-        expr = MulExpr(expr, right);
-      } else {
-        expr = DivExpr(expr, right);
-      }
-      skipSpaces();
-    }
-    // Handle percentage operator
-    skipSpaces();
-    if (!isEnd && current == '%') {
+        expr = op == '*' ? MulExpr(expr, right) : DivExpr(expr, right);
+      } else if (current == '%') {
         eat();
         expr = PercentExpr(expr);
+      } else {
+        // implicit multiplication
+        var right = parsePow();
+        expr = MulExpr(expr, right);
+      }
+      skipSpaces();
     }
     return expr;
   }

lib/screens/calculator_home_page.dart

@@ -48,7 +48,30 @@ class _CalculatorHomePageState extends State<CalculatorHomePage> {
     final input = _controller.text.trim();
     final normalizedInput = input.replaceAll(' ', '');
 
-    // 使用solver检查是否为可绘制的函数表达式
+    // 如果当前已经是函数模式，保持函数模式
+    if (_isFunctionMode) {
+      // 重新检查表达式是否仍然可绘制（以防用户修改了表达式）
+      if (_solverService.isGraphableExpression(normalizedInput)) {
+        // 保持在函数模式，不做任何改变
+        return;
+      } else {
+        // 表达式不再可绘制，切换回普通模式
+        setState(() {
+          _isFunctionMode = false;
+        });
+      }
+    }
+
+    // 检查是否为函数表达式（优先使用简单y=检测）
+    if (normalizedInput.toLowerCase().startsWith('y=')) {
+      setState(() {
+        _isFunctionMode = true;
+        _result = null;
+      });
+      return;
+    }
+
+    // 备用检查：使用solver进行更复杂的表达式检测
     if (_solverService.isGraphableExpression(normalizedInput)) {
       setState(() {
         _isFunctionMode = true;
@@ -57,6 +80,7 @@ class _CalculatorHomePageState extends State<CalculatorHomePage> {
       return;
     }
 
+    // 普通表达式求解
     setState(() {
       _isFunctionMode = false;
       _isLoading = true;

lib/widgets/graph_card.dart

@@ -54,6 +54,12 @@ class _GraphCardState extends State<GraphCard> {
         (match) => '${match.group(1)}*${match.group(2)}',
       );
 
+      // 在 % 和变量或数字之间插入乘号 (如 80%x -> 80%*x)
+      functionExpr = functionExpr.replaceAllMapped(
+        RegExp(r'%([a-zA-Z\d])'),
+        (match) => '%*${match.group(1)}',
+      );
+
       // 解析表达式
       final parser = Parser(functionExpr);
       final expr = parser.parse();

test/solver_test.dart

@@ -130,6 +130,10 @@ void main() {
       // 测试无y=前缀的表达式
       final noPrefix = solver.prepareFunctionForGraphing('(x-1)(x+3)');
       expect(noPrefix, 'x^2+2x-3');
+
+      // 测试百分比表达式
+      final percentExpr = solver.prepareFunctionForGraphing('y=80%x');
+      expect(percentExpr, '80%x');
     });
   });
 }