init commit

archive/design pattern/interpreter_calculator.cpp

@@ -0,0 +1,102 @@
+#include <iostream>
+#include <string.h>
+#include <stack>
+using namespace std;
+
+class AbstractExpression
+{
+public:
+    virtual int value() = 0;
+};
+
+class ValueExpression : public AbstractExpression
+{
+    int val;
+
+public:
+    ValueExpression(string val)
+    {
+        this->val = atoi(val.c_str());
+    }
+    int value()
+    {
+        return this->val;
+    }
+};
+
+class SymbolExpression : public AbstractExpression
+{
+    AbstractExpression *left, *right;
+    string symbol;
+
+public:
+    SymbolExpression(string symbol, AbstractExpression *left, AbstractExpression *right)
+    {
+        this->symbol = symbol;
+        this->left = left;
+        this->right = right;
+    }
+
+    int value()
+    {
+        // 非加即减
+        if (symbol == "+")
+        {
+            return left->value() + right->value();
+        }
+        else
+        {
+            return left->value() - right->value();
+        }
+    }
+};
+//expression=value|operator
+//value=number
+//operator='+'|'-'
+int main()
+{
+    char str[] = "1+4+5+6-7";
+    AbstractExpression *exp = new SymbolExpression("+", new ValueExpression("1"), new SymbolExpression("+", new ValueExpression("4"), new SymbolExpression("+", new ValueExpression("5"), new SymbolExpression("-", new ValueExpression("6"), new ValueExpression("7"))))); //反了
+    cout << "手动构建:" << exp->value() << endl;
+    stack<AbstractExpression *> stack;
+    AbstractExpression *expression;
+    for (int i = 0; i < strlen(str); i++)
+    {
+        if (str[i] >= '0')
+        {
+            string val;
+            for (; i < strlen(str); i++)
+            {
+                if (str[i] < '0')
+                {
+                    break;
+                }
+                val += str[i];
+            }
+            i--;
+            stack.push(new ValueExpression(val));
+        }
+        else
+        {
+            string symbol;
+            symbol += str[i++];
+            AbstractExpression *exp = stack.top();
+            stack.pop();
+            string val;
+            for (; i < strlen(str); i++)
+            {
+                if (str[i] < '0')
+                {
+                    break;
+                }
+                val += str[i];
+            }
+            i--;
+            stack.push(new SymbolExpression(symbol, exp, new ValueExpression(val)));
+        }
+    }
+    expression = stack.top();
+    cout << "value:" << expression->value() << endl;
+
+    return 0;
+}