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| A four-function postfix calculator. |
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#include <iostream>
#include <stack>
#include <string>
#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;
}
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