C++/Data Structure/Stack

A four-function postfix calculator.

<source lang="cpp">

1. include <iostream>
2. include <stack>
3. include <string>
4. include <cmath>

using namespace std; int main() {

 stack<double> stackObject;
 double a, b;
 string s;
 do {
   cout << ": ";
   cin >> s;
   switch( s[ 0 ]) {
     case "q": // quit the calculator
       break;
     case ".": // show top-of-stack
       cout << stackObject.top() << endl;
       break;
     case "+": // add
       if(stackObject.size() < 2) {
         cout << "Operand Missing\n";
         break;
       }
       a = stackObject.top();
       stackObject.pop();
       b = stackObject.top();
       stackObject.pop();
       cout << a + b << endl;
       stackObject.push(a + b);
       break;
     case "-": // subtract
       // see if user entering a negative number
       if(s.size() != 1) {
         // push value onto the stack
         stackObject.push(atof(s.c_str()));        
         break;
       }
       // otherwise, is a subtraction
       if(stackObject.size() < 2) {
         cout << "Operand Missing\n";
         break;
       }
       a = stackObject.top();
       stackObject.pop();
       b = stackObject.top();
       stackObject.pop();
       cout << b - a << endl;
       stackObject.push(b - a);
       break;
     case "*": // multiply
       if(stackObject.size() < 2) {
         cout << "Operand Missing\n";
         break;
       }
       a = stackObject.top();
       stackObject.pop();
       b = stackObject.top();
       stackObject.pop();
       cout << a*b << endl;
       stackObject.push(a*b);
       break;
     case "/": // divide
       if(stackObject.size() < 2) {
         cout << "Operand Missing\n";
         break;
       }
       a = stackObject.top();
       stackObject.pop();
       b = stackObject.top();
       stackObject.pop();
       cout << b/a << endl;
       stackObject.push(b/a);
       break;
     default:      
       // push value onto the stack
       stackObject.push(atof(s.c_str()));        
       break;
   }
 } while(s != "q");
 return 0;

}

      </source>

A simple stack example: push, empty, pop and top

<source lang="cpp">

1. include <iostream>
2. include <stack>

using namespace std; int main() {

 stack<char> stackObject;
 stackObject.push("A");
 stackObject.push("B");
 stackObject.push("C");
 stackObject.push("D");
 while(!stackObject.empty()) {
   cout << "Popping: ";
   cout << stackObject.top() << endl;
   stackObject.pop();
 }
 return 0;

}

      </source>