Implementation of algorithm to convert infix expressions to postfix and prefix expressions.

infixconversion.cpp

#include "lib/stack.hpp"
#include <iostream>
#include <string>
#include <cstring>
#include <algorithm>
#include <cctype>

using std::string;
using std::cin;
using std::cout;

class ArithmeticExpression{
    char operators[6] = {'/', '*', '+', '-', '^'};
    Stack<char> operatorstack;
    string expression;
    int precedence(char ops){
        int weight;
        switch(ops){
            case '(':
                weight = 5;
                break;
            case '^':
                weight = 4;
                break;
            case '/':
            case '*':
                weight = 3;
                break;
            case '+':
            case '-':
                weight = 2;
                break;
            default:
                weight = 1;
                break;
        }
        return weight;
        }
    public:
        ArithmeticExpression(string expression):expression(expression){ }
        string infixToPostfix(){
          int index = 0;
          string postfixexpr;
          while(index <= expression.length()){
            char token = expression[index];
            if(token == ' ' || token == '\t') { }
            else if(std::isalpha(token)){
                postfixexpr += token;
            }
            else if(std::strchr(operators,token)!=NULL){
               while(
                   !operatorstack.empty()
                   && (precedence(token) <= precedence(operatorstack.top()))
                   && operatorstack.top()!='(' 
                    ) {
                        postfixexpr += operatorstack.top();
                        operatorstack.pop();
                    }
               operatorstack.push(token);
            }
            else if(token == '('){
                operatorstack.push(token);
            }
            else if(token == ')'){
                while(!operatorstack.empty() && operatorstack.top()!='('){
                    postfixexpr += operatorstack.top();
                    operatorstack.pop();
                }
                operatorstack.pop();
            }
            index++;
          }
          while(!operatorstack.empty()){
                postfixexpr += operatorstack.top();
                operatorstack.pop();
          }
        return postfixexpr;
        }

        string infixToPrefix(){
            std::reverse(expression.begin(), expression.end());
            cout << expression << '\n';
            for(char& c:expression){
                if(c =='('){
                    c = ')';
                }
                else if( c== ')'){
                    c = '(';
                }
            }
            cout << expression << '\n';
            string prefixexpr = infixToPostfix();
            cout << prefixexpr << '\n';
            std::reverse(prefixexpr.begin(), prefixexpr.end());
            cout << prefixexpr << '\n';
            std::reverse(expression.begin(), expression.end());
            for(char& c:expression){
                if(c =='('){
                    c = ')';
                }
                else if( c== ')'){
                    c = '(';
                }
            }
            return prefixexpr;
        }
};


int main(int argc, char* argv[]){
             string expression; //"a+(b*c-(d/e-f)*g)*h";
             cout << "Enter expression: "; std::cin >> expression;
             ArithmeticExpression abcd(expression);
             cout << abcd.infixToPrefix();
             return 0;
}