PrefixEval.cpp

#include <bits/stdc++.h> 
using namespace std; 
  
bool isOperand(char c) 
{ 
    return isdigit(c); 
} 
  
double evalPrefix(string exprsn) 
{ 
    stack<double> Stack; 
  
    for (int j = exprsn.size() - 1; j >= 0; j--) { 
  
        
        if (isOperand(exprsn[j])) 
            Stack.push(exprsn[j] - '0'); 
  
        else {
            double o1 = Stack.top(); 
            Stack.pop(); 
            double o2 = Stack.top(); 
            Stack.pop(); 
  
            switch (exprsn[j]) { 
            case '+': 
                Stack.push(o1 + o2); 
                break; 
            case '-': 
                Stack.push(o1 - o2); 
                break; 
            case '*': 
                Stack.push(o1 * o2); 
                break; 
            case '/': 
                Stack.push(o1 / o2); 
                break; 
            } 
        } 
    } 
  
    return Stack.top(); 
} 

int main() 
{ 
    string exprsn = "+9*26"; 
    cout << evalPrefix(exprsn) << endl; 
    return 0; 
}