Evaluate postfix (Reverse Polish notation) is a notation in which every operator follows all of its operands. Program to evaluate postfix notation using stack and print the value.

Infix and postfix are the notations to write the expressions. The infix notation put operators in between the operands. The postfix notation put operators after their operands. Write a program convert from infix notation to postfix notation.

Write a program to read the symbol string from the user. The program should validate the symbols using the stack. Stack uses push and pop operations for validating the symbol.

A stack is a basic data structure that insert and remove the items using last in first out (LIFO) strategy. The stack is a very powerful data structure. The stack can used when add or remove the element using last in first out order.