infixToPrefix.cpp

#include <bits/stdc++.h>
#include "MYSTACK.h"

using namespace std;

int precisionCalc(char c)
{
    if (c == '^')
    {
        return 3;
    }
    else if (c == '/' || c == '*')
    {
        return 2;
    }
    else if (c == '+' || c == '-')
    {
        return 1;
    }
    else
        return -1;
}

string infixToPrefix(string chk)
{

    reverse(chk.begin(), chk.end()); // ) --> Opening AND ( --> Closing
    Stack<char> st;
    string result;

    for (int i = 0; i < chk.length(); i++)
    {

        if ((chk[i] >= 'a' && chk[i] <= 'z') || (chk[i] >= 'A' &&  chk[i] <= 'Z'))//(chk[i] >= '0' && chk[i] <= '9') // 
        {
            result += chk[i];
        }
        else if (chk[i] == ')')
        {
            st.push(chk[i]);
        }
        else if (chk[i] == '(')
        {
            while (!st.empty() && st.Top() != ')')
            {
                result += st.pop();
            }
            if (!st.empty())
                st.pop();
        }
        else
        {
            while (!st.empty() && precisionCalc(st.Top()) >= precisionCalc(chk[i]))
            {
                result += st.pop();
            }
            st.push(chk[i]);
        }
    }

    while(!st.empty()){
        result+=st.pop();
    }

    reverse(result.begin(),result.end());
    return result;

}

int prefixEvaluation(string chk)
{

    Stack<int> st;

    for (int i = chk.length() - 1; i >= 0; i--)
    {
        if (chk[i] >= '0' && chk[i] <= '9') // chk[i] 0 to 9 --> Operand
        {
            st.push(chk[i] - '0');
        }
        else // chk[i] ---> Operator
        {
            int a = st.pop();
            int b = st.pop();

            switch (chk[i])
            {
            case '+':
                st.push(a + b);
                break;
            case '-':
                st.push(a - b);
                break;
            case '*':
                st.push(a * b);
                break;
            case '/':
                st.push(a / b);
                break;
            case '^':
                st.push(pow(a, b));
                break;
            default:
                break;
            }
        }
    }
    return st.Top();
}

/*
+*423
-+7*45+20
(7+(4*5))-(2+0)
((A^B*C)-D)+((E/F)/(G+H))
*/

int main()
{
    string infix = "((A^B*C)-D)+((E/F)/(G+H))";
    string prefix;
    prefix = infixToPrefix(infix);
    cout << endl << prefix << endl;
        //  << prefixEvaluation(prefix) << endl
        //  << endl;
}