Program to convert infix to postfix expression in C++

#include <iostream>
#include <stack>
#include <string>

// Function to check if a character is an operator
bool isOperator(char c) {
    return (c == '+' || c == '-' || c == '*' || c == '/');
}

// Function to determine the precedence of an operator
int precedence(char c) {
    if (c == '+' || c == '-')
        return 1;
    if (c == '*' || c == '/')
        return 2;
    return 0; // Assuming '(' has the lowest precedence
}

// Function to convert infix expression to postfix
std::string infixToPostfix(const std::string& infix) {
    std::string postfix = "";
    std::stack<char> operatorStack;

    for (char c : infix) {
        if (isalnum(c)) {
            postfix += c; // If it's an operand, add to the postfix expression
        } else if (c == '(') {
            operatorStack.push(c); // Push '(' onto the stack
        } else if (c == ')') {
            // Pop operators from the stack and add to postfix until '(' is encountered
            while (!operatorStack.empty() && operatorStack.top() != '(') {
                postfix += operatorStack.top();
                operatorStack.pop();
            }
            // Pop '(' from the stack (removing the matching '(')
            if (!operatorStack.empty() && operatorStack.top() == '(') {
                operatorStack.pop();
            }
        } else if (isOperator(c)) {
            // Pop operators with higher or equal precedence from the stack and add to postfix
            while (!operatorStack.empty() && operatorStack.top() != '(' &&
                   precedence(c) <= precedence(operatorStack.top())) {
                postfix += operatorStack.top();
                operatorStack.pop();
            }
            // Push the current operator onto the stack
            operatorStack.push(c);
        }
    }

    // Pop any remaining operators from the stack and add to postfix
    while (!operatorStack.empty()) {
        postfix += operatorStack.top();
        operatorStack.pop();
    }

    return postfix;
}

int main() {
    std::string infixExpression;
    std::cout << "Enter an infix expression: ";
    std::cin >> infixExpression;

    std::string postfixExpression = infixToPostfix(infixExpression);
    std::cout << "Postfix expression: " << postfixExpression << std::endl;

    return 0;
}