infix to prefix conversion

#include<bits/stdc++.h>
using namespace std;

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

//--------------------------------------------------
/*
Algorithm -
* Suppose your expression is 
  -> ( a - b/c )*( a/k - l )
  -> reverse this expression
  -> ) l - k/a (*) c/b - a (
  -> reverse the brackets
  -> ( l - k/a )*( c/b - a )

* If operand
   -> print
* If '('
   -> push to stack
* If ')'
   -> pop from stack and print until '(' is found
* If operator
   -> pop from stack and print until an operator 
   -> with less or equal(major change here) precedence is found
*/

string infixToPrefix(string s) {
    stack<char> st;
    string res;

    reverse(s.begin(), s.end());
    for (int i = 0; i < s.length(); i++)
    {
        if(s[i] == '(')
          s[i] = ')';
        else if(s[i] == ')')
          s[i] = '(';
    }
    

    for (int i = 0; i < s.length(); i++)
    {
        if(s[i] == ' ') {
            continue;
        }
        else if((s[i] >= 'a' && s[i] <= 'z') || (s[i] >= 'A' && s[i] <= 'Z')) {
            res += s[i];
        }
        else if(s[i] == '(') {
            st.push(s[i]);
        }
        else if(s[i] == ')') {
            while (!st.empty() && st.top() != '(')
            {
                res += st.top();
                st.pop();
            }
            if(!st.empty()) {
                st.pop(); // Popping '(' here
            }
        }
        else {
            while (!st.empty() && prec(st.top()) > prec(s[i]))
            {
                res += st.top();
                st.pop();
            }
            st.push(s[i]);
        }
    }
    
    while (!st.empty())
    {
       res += st.top();
       st.pop();
    }
    
    reverse(res.begin(), res.end());
    return res;
}

int main() {
    string exp = "a*(b-c+d)/e";
    cout<<infixToPrefix(exp);
    return 0;
}