Support for negative numbers, PI and E can be used directly.

README.md

@@ -34,7 +34,7 @@ Result: 7.000000
 ```
 
 ```shell
-sin(PI()/2)*6-tan(atan(6))
+sin(PI/2)*6-tan(atan(6))
 
 Result: -0.000000
 ```
@@ -49,6 +49,12 @@ fuck(6)+7
 [Function Not Found]: fuck.
 ```
 
+```shell
+-10-(2*(-PI))+E
+
+Result: -0.998533
+```
+
 ### 在`example/xCalc.cpp`中
 
 使用`addFunc`接口添加`if`、`fib`、`hello`等指令。

src/expression_calc.cpp

@@ -253,7 +253,44 @@ double eXpressionCalc::evalNotation(const Notation_t& notation) {
 }
 
 void eXpressionCalc::setExpression(Expression_t expression) {
-    Expr = std::move(expression);
+    std::string modified_expr = expression;
+
+    // 1. If the first character is '-', prepend '0' for negative number
+    if (!modified_expr.empty() && modified_expr[0] == '-') {
+        modified_expr = "0" + modified_expr;  // Change "-2" to "0-2"
+    }
+
+    // 2. Replace all "(-" with "(0-" to handle negative numbers in parentheses
+    size_t pos = 0;
+    while ((pos = modified_expr.find("(-", pos)) != std::string::npos) {
+        modified_expr.replace(pos, 2, "(0-");
+        pos += 3;  // Skip past "(0-"
+    }
+
+    // 3. Append "()" to "PI" if not followed by '('
+    pos = 0;
+    while ((pos = modified_expr.find("PI", pos)) != std::string::npos) {
+        if (pos + 2 >= modified_expr.size() || modified_expr[pos + 2] != '(') {
+            modified_expr.insert(pos + 2, "()");
+            pos += 4;  // Skip over "PI()"
+        } else {
+            pos += 3;  // Skip over "PI("
+        }
+    }
+
+    // 4. Append "()" to "E" if not followed by '('
+    pos = 0;
+    while ((pos = modified_expr.find("E", pos)) != std::string::npos) {
+        if (pos + 1 >= modified_expr.size() || modified_expr[pos + 1] != '(') {
+            modified_expr.insert(pos + 1, "()");
+            pos += 3;  // Skip over "E()"
+        } else {
+            pos += 2;  // Skip over "E("
+        }
+    }
+
+    // 5. Assign the processed expression to internal member
+    Expr = std::move(modified_expr);
 }
 
 const Error_t& eXpressionCalc::getError() {

test.sh

@@ -7,13 +7,15 @@ popd
 calc_bin=./build/xCalc
 
 echo '
-if(sin(20)
-  (cos(20) + PI())
-  (sin(PI()) - 20)
+if(sin(-20)
+  (cos(20) + PI)
+  (sin(-PI) - 20)
 ) + 30;
 hello()
 ' | $calc_bin
 
 for i in {1..100}; do
   echo "fib(1, 1, $i) / fib(1, 1, $i - 1)" | $calc_bin
 done
+
+echo '-10-(2*(-PI))+E' | $calc_bin