refactory the code

Author: haoel

algorithms/cpp/evaluateReversePolishNotation/evaluateReversePolishNotation.cpp

@@ -26,61 +26,56 @@ using namespace std;
 
 
 class Solution {
-#define ERROR  err=false;continue
 public:
     int evalRPN(vector<string> &tokens) {
         int i =0;
         bool err = false;
         vector<int> exp;
         for (int i=0; i<tokens.size() && !err; i++ ){
-            if( isOp(tokens[i])==true ) {
-                if (exp.size() >= 2) {
-                    int lhs, rhs;
-                    rhs = exp.back();
-                    exp.pop_back();
-                    lhs = exp.back();
-                    exp.pop_back();
-
-                    int evlValue;
-                    if (tokens[i]=="+"){
-                        evlValue = lhs + rhs;    
-                    }else if (tokens[i]=="-"){
-                        evlValue = lhs - rhs;
-                    }else if (tokens[i]=="*"){
-                        evlValue = lhs * rhs;
-                    }else if (tokens[i]=="/"){
-                        evlValue = lhs / rhs;
-                    }
-                    
-                    exp.push_back(evlValue);
-                        
-                }else{
-                    ERROR;
-                }
-            }else if (isNum(tokens[i])) {
+            if (isNum(tokens[i])) {
                 exp.push_back(value);
+            } else if( isOp(tokens[i])==true ) {
+                if (exp.size() < 2) {
+                    return 0; //ERROR
+                }
+                int lhs, rhs;
+                rhs = exp.back();
+                exp.pop_back();
+                lhs = exp.back();
+                exp.pop_back();
+
+                int evlValue;
+                if (tokens[i]=="+"){
+                    evlValue = lhs + rhs;    
+                }else if (tokens[i]=="-"){
+                    evlValue = lhs - rhs;
+                }else if (tokens[i]=="*"){
+                    evlValue = lhs * rhs;
+                }else if (tokens[i]=="/"){
+                    evlValue = lhs / rhs;
+                }
+
+                exp.push_back(evlValue);
+
             }else {
-                ERROR;
+                return 0; //ERROR 
             }
         }
-        if (err==true){
-            return 0;
-        }
-        
+
         if (exp.size()==1){
             return exp.back();
         }
         return 0;        
-                
+
     }
-    
+
 private:
     long value;
-    
+
     bool isOp(string &op) {
         return (op=="+" || op=="-" || op=="*" || op=="/");
     }
-    
+
     bool isNum(string &num) {
         char *end;
         value = strtol(num.c_str(), &end, 10); 
@@ -97,7 +92,7 @@ int main()
     Solution s;
     char exps[5][3] = {"42", "9", "6", "-", "+"};
     vector<string> expression;
-    
+
     cout << "Expression: \n    ";
     for (int i=0; i<5; i++){
         expression.push_back(exps[i]);