Evaluation of a Prefix Expression Multiple Choice Questions and Answers (MCQs)

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This set of Data Structures & Algorithms Multiple Choice Questions & Answers (MCQs) focuses on “Evaluation of a Prefix Expression”.

1. How many stacks are required for evaluation of prefix expression?
a) one
b) two
c) three
d) four
View Answer

Answer: b
Explanation: 2 stacks are required for evaluation of prefix expression, one for integers and one for characters.
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2. While evaluating a prefix expression, the string is read from?
a) left to right
b) right to left
c) center to right
d) center to left to right
View Answer

Answer: b
Explanation: The string is read from right to left because a prefix string has operands to its right side.

3. The associativity of an exponentiation operator ^ is right side.
a) True
b) False
View Answer

Answer: a
Explanation: The associativity of ^ is right side while the rest of the operators like +,-,*,/ has its associativity to its left.
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4. How many types of input characters are accepted by this algorithm?
a) one
b) two
c) three
d) four
View Answer

Answer: c
Explanation: Three kinds of input are accepted by this algorithm- numbers, operators and new line characters.

5. What determines the order of evaluation of a prefix expression?
a) precedence and associativity
b) precedence only
c) associativity only
d) depends on the parser
View Answer

Answer: a
Explanation: Precedence is a very important factor in determining the order of evaluation. If two operators have the same precedence, associativity comes into action.
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6. Find the output of the following prefix expression.

*+2-2 1/-4 2+-5 3 1

a) 2
b) 12
c) 10
d) 4
View Answer

Answer: a
Explanation: The given prefix expression is evaluated using two stacks and the value is given by (2+2-1)*(4-2)/(5-3+1)= 2.
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7. An error is thrown if the character ‘\n’ is pushed in to the character stack.
a) true
b) false
View Answer

Answer: b
Explanation: The input character ‘\n’ is accepted as a character by the evaluation of prefix expression algorithm.

8. Using the evaluation of prefix algorithm, evaluate +-9 2 7.
a) 10
b) 4
c) 17
d) 14
View Answer

Answer: d
Explanation: Using the evaluation of prefix algorithm, +-9 2 7 is evaluated as 9-2+7=14.
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9. If -*+abcd = 11, find a, b, c, d using evaluation of prefix algorithm.
a) a=2, b=3, c=5, d=4
b) a=1, b=2, c=5, d=4
c) a=5, b=4, c=7,d=5
d) a=1, b=2, c=3, d=4
View Answer

Answer: b
Explanation: The given prefix expression is evaluated as ((1+2)*5)-4 = 11 while a=1, b=2, c=5, d=4.

10. In the given C snippet, find the statement number that has error.

//C code to push an element into a stack
1. void push( struct stack *s, int x) 
2. {
3.     if(s->top==MAX-1)
4.     {
5.         printf(“stack overflow”);
6.     }
7.     else
8.     {
9.         s->items[++s->top]=x;
10.        s++;
11.    }   
12. }

a) 1
b) 9
c) 10
d) 11
View Answer

Answer: c
Explanation: If the stack is not full then we are correctly incrementing the top of the stack by doing “++s->top” and storing the value of x in it. However, in the next statement “s++”, we are un-necessarily incrementing the stack base pointer which will lead to memory corruption during the next push() operation.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn | Youtube | Instagram | Facebook | Twitter