calculator: add implementation

calculator.cc

@@ -2,8 +2,69 @@
 
 namespace dev {
 
-double Calculator::evaluate(std::string expression) {
-    return 0;
+bool Calculator::IsOperator(char c){
+    switch (c){
+        case '+':
+        case '-':
+        case '*':
+        case '/':
+            return true;
+        default:
+            return false;
+    }
 }
 
-}  // namespace calculator
+double Calculator::evaluate(std::string expression) 
+{
+    double ret =0.0;
+    float v1,v2;
+    v1=v2=0;
+    for(int i=0;i < expression.length();i++)
+    {
+        if (isspace(expression[i])){
+            continue;
+        }
+
+        if(isdigit(expression[i]))
+        {
+            std::string str(1,expression[i]);
+            mStack.push(std::stof(str));
+        }
+        else if (IsOperator(expression[i])){
+            if (expression[i] == '+'){
+                v1 = mStack.top();
+                mStack.pop();
+                v2 = mStack.top();
+                mStack.pop();
+                ret = v1+v2;
+            }
+            if (expression[i] == '-'){
+                v1 = mStack.top();
+                mStack.pop();
+                v2 = mStack.top();
+                mStack.pop();
+                ret = v1-v2;
+            }
+            if (expression[i] == '*'){
+                v1 = mStack.top();
+                mStack.pop();
+                v2 = mStack.top();
+                mStack.pop();
+                ret = v1*v2;
+            }
+            if (expression[i] == '/'){
+                v1 = mStack.top();
+                mStack.pop();
+                v2 = mStack.top();
+                mStack.pop();
+                ret = v2/v1;
+            }
+
+            mStack.push(ret);
+        }
+        }
+    //Return answer
+    return mStack.top();
+}
+
+}  // namespace dev

calculator.h

@@ -1,5 +1,5 @@
 #include<string>
-
+#include<stack>
 namespace dev {
 
 class Calculator {
@@ -8,7 +8,10 @@ class Calculator {
     ~Calculator() = default;
 
     double evaluate(std::string expression);
-
+
+private:
+    std::stack<float> mStack;
+    bool IsOperator(char c);   
 };
 
 }  // namespace calculator

project.cc

@@ -1,10 +1,15 @@
+#include<iostream>
 #include "project.h"
 #include "calculator.h"
 namespace dev {
 
 int Project::run() {
   Calculator calc;
-  calc.evaluate("2 3 +");
+  std::string s;
+  std::cout<<"enter the string: ";
+  std::getline(std::cin,s);
+
+  std::cout<<"Result:"<<calc.evaluate(s)<<std::endl;
   return 0;
 }
 }  // namespace dev