StacksINFIX_POSTFIX.cpp

#include<iostream>
#include<stack>
#include <bits/stdc++.h>
using namespace std;
// 
// Function to return precedence of operators
int prec(char c) {
	if (c == '^')
		return 3;
	else if (c == '/' || c == '*')
		return 2;
	else if (c == '+' || c == '-')
		return 1;
	else
		return -1;
}
// 
// Function to return associativity of operators
char associativity(char c) {
	if (c == '^')
		return 'R';
	return 'L'; // Default to left-associative
}
// 
// The main function to convert infix expression
// to postfix expression
void infixToPostfix(string s) {
	stack<char> st;
	string result;

	for (int i = 0; i < s.length(); i++) {
		char c = s[i];
// 
		// If the scanned character is
		// an operand, add it to the output string.
		if ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9'))
			result += c;
// 
		// If the scanned character is an
		// ‘(‘, push it to the stack.
		else if (c == '(')
			st.push('(');
// 
		// If the scanned character is an ‘)’,
		// pop and add to the output string from the stack
		// until an ‘(‘ is encountered.
		else if (c == ')') {
			while (st.top() != '(') {
				result += st.top();
				st.pop();
			}
			st.pop(); // Pop '('
		}
		// If an operator is scanned
		else {
			while (!st.empty() && prec(s[i]) < prec(st.top()) ||
				!st.empty() && prec(s[i]) == prec(st.top()) &&
				associativity(s[i]) == 'L') {
				result += st.top();
				st.pop();
			}
			st.push(c);
		}
	}
// 
	// Pop all the remaining elements from the stack
	while (!st.empty()) {
		result += st.top();
		st.pop();
	}
// 
	cout << result << endl;
}
// 
// Driver code
int main() {
	string exp = "a+b*(c^d-e)^(f+g*h)-i";
// 
	// Function call
	infixToPostfix(exp);
// 
	return 0;
}
// 
// 
// .....................Postfix evaluation.........................
// 
// 
#include <iostream>
#include <stack>
#include <string>
#include <cmath>
using namespace std;

bool isOperator(char c) {
    return c == '+' || c == '-' || c == '*' || c == '/' || c == '^';
}

int performOperation(char operation, int operand1, int operand2) {
    switch (operation) {
        case '+': return operand1 + operand2;
        case '-': return operand1 - operand2;
        case '*': return operand1 * operand2;
        case '/': return operand1 / operand2;
        case '^': return pow(operand1, operand2);
        default: return 0;
    }
}

int evaluatePostfix(const string& expression) {
    stack<int> operands;

    for (char c : expression) {
        if (isdigit(c)) {
            operands.push(c - '0');
        } else if (isOperator(c)) {
            int operand2 = operands.top();
            operands.pop();
            int operand1 = operands.top();
            operands.pop();
            operands.push(performOperation(c, operand1, operand2));
        }
    }
    return operands.top();
}

int main() {
    string postfixExpression;
    cout << "Enter a postfix expression: ";
    getline(cin, postfixExpression);

    int result = evaluatePostfix(postfixExpression);
    cout << "Result: " << result << endl;

    return 0;
}