A: Find the number of ways of putting 5 letters in the envelope in such a way that no letter is being put in the right envelope. B. In a holiday party, each 6 attendants brings in a gift and exchanges it with someone

else in the party. Find the number of ways of exchanging so that no one gets his/her gift back.

C. If you have 7 pairs of parentheses then how many valid groups of them one can make?

D. The number of ways one can triangulate a regular polygon with 5 sides is…?

Microsoft introduced active directory with windows 2000. in server 2012, it is in now version 4. what are some new features in the new ad that were not present in windows 2000 ad?

To hide gridline when you display or print a worksheet

We as humans write math expression in infix notation, e.g. 5 + 2 (the operators are written in-between the operands). in a computer’s language, however, it is preferred to have the operators on the right side of the operands, i.e. 5 2 +. for more complex expressions that include parenthesis and multiple operators, a compiler has to convert the expression into postfix first and then evaluate the resulting postfix.write a program that takes an “infix” expression as input, uses stacks to convert it into postfix expression, and finally evaluates it. it must support the following operations: + - / * ^ % (example infix expression: (7 - 3) / (2 + 2)postfix expression: 7 3 - 2 2 + /result: 1guidelines: 1. you will need to use stacks in three placesa. one for the parenthesis check [char stack]b. one during infix to postfix [char stack]c. one during evaluation [int stack]for a and b above, you can use same array and same push, pop method as both ofthem are char. but for evaluation you have int stack and you might consider to createanother push pop method to handle it. maybe push_int, pop_int, etc. or find otherstrategy to utilize existing push pop method2. you can create a function for obtaining operator priority. that function should take anoperator as input and return its priority as an integer. this function will you a lot andreduce repeated code3. during evaluation you will need to convert char into integer. example for single digit: char c = '5'; int x = c - '0';