Lecture 243:- Let's Code Infix to Postfix Conversion

Below is a C++ implementation of the Infix to Postfix conversion using the stack method:

cppCopy code

#include <iostream> #include <stack> #include <string> #include <cctype> int precedence(char op) {    if (op == '+' || op == '-')        return 1;    else if (op == '*' || op == '/')        return 2;    return 0; } std::string infixToPostfix(const std::string& infix) {    std::stack<char> operatorStack;    std::string postfix;    for (char c : infix) {        if (std::isspace(c)) {            continue; // Skip whitespaces        } else if (std::isalnum(c)) {            postfix += c; // Operand, append to postfix string        } else if (c == '(') {            operatorStack.push(c);        } else if (c == ')') {            while (!operatorStack.empty() && operatorStack.top() != '(') {                postfix += ' '; // Add a space between consecutive operands                postfix += operatorStack.top();                operatorStack.pop();            }            operatorStack.pop(); // Pop and discard the opening parenthesis        } else { // Operator            while (!operatorStack.empty() && operatorStack.top() != '(' &&                   precedence(operatorStack.top()) >= precedence(c)) {                postfix += ' '; // Add a space between consecutive operands                postfix += operatorStack.top();                operatorStack.pop();            }            postfix += ' '; // Add a space between consecutive operands            operatorStack.push(c);        }    }    while (!operatorStack.empty()) {        postfix += ' '; // Add a space between consecutive operands        postfix += operatorStack.top();        operatorStack.pop();    }    return postfix; } int main() {    std::string infix, postfix;    std::cout << "Enter an infix expression: ";    std::getline(std::cin, infix);    postfix = infixToPostfix(infix);    std::cout << "Postfix expression: " << postfix << std::endl;    return 0; }

This implementation follows the same Infix to Postfix conversion algorithm described earlier using the stack method. The precedence function assigns a precedence level to each operator. The infixToPostfix function iterates through each character in the infix expression and performs the necessary operations based on the type of character (operand, operator, parentheses, etc.).

The resulting postfix expression is printed with spaces between consecutive operands and operators for better readability. This is not required for postfix expressions to be valid but can be helpful in understanding the output.

In the main function, the user is prompted to enter an infix expression. The program then calls the infixToPostfix function to convert the infix expression to postfix and prints the resulting postfix expression.