Four-function postfix calculator. - C++ STL

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Description

Four-function postfix calculator.

Demo Code

#include <iostream>
#include <stack>
#include <string>
#include <cmath>
using namespace std;
int main()/*from  www  .  j  a v  a2  s  .com*/
{
   stack<double> stck;
   double a, b;
   string s;
   do {
      cout << ": ";
      cin >> s;
      switch(s[0]) {
         case 'q': // quit the calculator
         break;
         case '.': // show top-of-stack
         cout << stck.top() << "\n";
         break;
         case '+': // add
         if(stck.size() < 2) {
            cout << "Operand Missing\n";
            break;
         }
         a = stck.top();
         stck.pop();
         b = stck.top();
         stck.pop();
         cout << a+b << "\n";
         stck.push(a+b);
         break;
         case '-': // subtract
         // See if user entered a negative number.
         if(s.size() != 1) {
            // Push value onto the stack.
            stck.push(atof(s.c_str()));
            break;
         }
         // otherwise, is a subtraction
         if(stck.size() < 2) {
            cout << "Operand Missing\n";
            break;
         }
         a = stck.top();
         stck.pop();
         b = stck.top();
         stck.pop();
         cout << b-a << "\n";
         stck.push(b-a);
         break;
         case '*': // multiply
         if(stck.size() < 2) {
            cout << "Operand Missing\n";
            break;
         }
         a = stck.top();
         stck.pop();
         b = stck.top();
         stck.pop();
         cout << a*b << "\n";
         stck.push(a*b);
         break;
         case '/': // divide
         if(stck.size() < 2) {
            cout << "Operand Missing\n";
            break;
         }
         a = stck.top();
         stck.pop();
         b = stck.top();
         stck.pop();
         cout << b/a << "\n";
         stck.push(b/a);
         break;
         default:
         // push value onto the stack
         stck.push(atof(s.c_str()));
         break;
      }
   } while(s != "q");
   return 0;
}

Result


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