評價後綴函數

Question

下面我試圖編寫一個評估後綴表達式的程序。但是，我注意到，我設置的兩個要素未被設置爲正確的值。我仍然在學習C++庫中的堆棧特性，所以如果有人能解釋爲什麼會發生這種情況，我將不勝感激！

/*Sample output: 
Enter an infix or prefix expression:3+4-1 
Postfix is: 34+1- 
postFix[i]: 3 
postFix[i]: 4 
element1: 52 
element2: 51 
val is: 103 
postFix[i]: 1 
element1: 49 
element2: 103 
val is: 54 
Value is 54*/ 

int evaluatePostfix (string postFix) 
{ 
    stack<int> operands; 

     int length = postFix.length(); 
     int val = 0; 
     for (int i = 0; i < length; i++) 
     { 
       //if the char is a digit push the digit onto the stack 
       if(isdigit(postFix[i])) 
       { 
         operands.push(postFix[i]); 
         cout << "postFix[i]: " << postFix[i] << endl; 
       } 
       else if (isOperator(postFix[i])) 
       { 
         // 
         //element 1 and element 2 will be the element on the top of the stack 
         // 
         int element1 = operands.top(); 
         cout << "element1: " << element1 << endl; 
         operands.pop(); 
         int element2 = operands.top(); 
         cout << "element2: " << element2 << endl; 
         operands.pop(); 
         // 
         //create a switch statement that evaluates the elements based on the operator 
         // 
         switch(postFix[i]) 
         { 
           case '+': 
             val = element2 + element1; 
             cout << "val is: " << val << endl; 
             operands.push(val); 
             break; 
           case '-': 
             val = element2 - element1; 
             cout << "val is: " << val << endl; 
             operands.push(val); 
             break; 
           case '*': 
             val = element2 * element1; 
             operands.push(val); 
             break; 
           case '/': 
             val = element2/element1; 
             operands.push(val); 
             break; 
           default: 
             return 0; 
         } 

                       } 

     } 
     return val; 
} 

Answer 1

的問題是你的後綴是一個字符串，當你把這些字符（這是有效的整數），你得到的ascii值回（例如51，52）。那些對應於正確的數字（例如3,4）

你最終得到的是一個偏移48的值，它對應於0符號。