## 1. What is the other name for a postfix expression?

**a) Normal polish Notation****b) Reverse polish Notation****c) Warsaw notation****d) Infix notation**

**Answer: b**

**Explanation: **

**Reverse polish Notation is the other name for a postfix expression whereas Polish Notation, Warsaw notation are the other names for a prefix expression.**

## 2. Which of the following is an example for a postfix expression?

**a) a*b(c+d)****b) abc*+de-+****c) +ab****d) a+b-c**

**Answer: b**

**Explanation: **

**abc*+de-+ is a postfix expression. +ab is a prefix expression and others are infix expressions.**

## 3. Reverse Polish Notation is the reverse of a Polish Notation.

**a) True****b) False**

**Answer: b**

**Explanation:**

**Reverse Polish Notation is not the reverse of a polish notation. Though both NPN and RPN read the expression from left to right, they follow different strategies.**

## 4. What is the time complexity of evaluation of postfix expression algorithm?

**a) O (N)****b) O (N log N)****c) O (N2)****d) O (M log N)**

**Answer: a**

**Explanation: **

**The time complexity of evaluation of infix, prefix and postfix expressions is O (N).**

## 5. In Postfix expressions, the operators come after the operands.

**a) True****b) False**

**Answer: a**

**Explanation:**

** In postfix expressions, the operators follow operands. In prefix expressions, the operands follow operators.**

## 6. Which of these operators have the highest order of precedence?

**a) ‘(‘ and ‘)’****b) ‘*’ and ‘/’****c) ‘~’ and ‘^’****d) ‘+’ and ‘-‘**

**Answer: c**

**Explanation:**

** The highest order of precedence is ~ and ^ followed by ‘*’ ,’ /’, ‘+’ ,’-‘ and then braces ‘(‘ ‘)’.**

## 7. Which of the following is not an application of stack?

**a) evaluation of postfix expression****b) conversion of infix to postfix expression****c) balancing symbols****d) line at ticket counter**

**Answer: d**

**Explanation:**

**Line at ticket counter is an application of queue whereas conversion of infix to postfix expression, balancing symbols, line at ticket counter are stack applications.**

## 8. While evaluating a postfix expression, when an operator is encountered, what is the correct operation to be performed?

**a) push it directly on to the stack****b) pop 2 operands, evaluate them and push the result on to the stack****c) pop the entire stack****d) ignore the operator**

**Answer: b**

**Explanation:**

**When an operator is encountered, the first two operands are popped from the stack, they are evaluated and the result is pushed into the stack.**

** **

## 9. Which of the following statement is incorrect?

**a) Postfix operators use value to their right****b) Postfix operators use value to their left****c) Prefix operators use value to their right****d) In postfix expression, operands are followed by operators**

**Answer: a**

**Explanation:**

**All prefix operators use values to their right and all postfix operators use values to their left.**

## 10. What is the result of the given postfix expression? abc*+ where a=1, b=2, c=3.

**a) 4****b) 5****c) 6****d) 7**

**Answer: d**

**Explanation:**

**The infix expression is a+b*c. Evaluating it, we get 1+2*3=7.**

## 11. What is the result of the following postfix expression? ab*cd*+ where a=2,b=2,c=3,d=4.

**a) 16****b) 12****c) 14****d) 10**

**Answer: a**

**Explanation:**

**The infix expression is a*b+c*d. Evaluating it, we get, 2*2+3*4=16.**

##
12. Consider the stack
| 5 |
| 4 |
| 3 |
| 2 |.
At this point, ‘*’ is encountered. What has to be done?

**a) 5*4=20 is pushed into the stack****b) * is pushed into the stack****c) 2*3=6 is pushed into the stack****d) * is ignored**

**Answer: a**

**Explanation:**

**When an operator is encountered, the first two operands of the stack are popped, evaluated and the result is pushed into the stack.**

## 13. Evaluate the postfix expression ab + cd/- where a=5, b=4, c=9, d=3.

**a) 23****b) 15****c) 6****d) 10**

**Answer: c**

**Explanation:**

**The infix expression is (a+b)-c/d. Evaluating it, (5+4)-9/3 gives 6.**

## 14. Evaluate and write the result for the following postfix expression abc*+de*f+g*+ where a=1, b=2, c=3, d=4, e=5, f=6, g=2.

**a) 61****b) 59****c) 60****d) 55**

**Answer: b**

**Explanation:**

**The infix expression is a+b*c+(d*e+f)*g. Evaluating it, 1+2*3+(4*5+6)*2 gives 59.**

## 15. For the given expression tree, write the correct postfix expression. The given expression tree gives the infix expression a+b*c

**a) abc*+****b) abc+*****c) ab+c*****d) a+bc***

**Answer: a**

**Explanation:**

**Evaluating the given expression tree gives the infix expression a+b*c. Converting it to postfix, we get, abc*+.**

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