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Objective Type Set
Online MCQ Assignment
Question Solution
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1. Which of the following code skips the first 20 iterations ?
a)

for(i in 1:100) {
             if(i <= 20) {
                next
      }
}

b)

for(i in 1:100) {
           if(i <= 19) {
           next
       }
}

c)

for(i in 1:100) {
         if(i <= 21) {
         next
      }
}

d) All of the mentioned

View Answer

Answer: a [Reason:] next is used to skip an iteration of a loop.

2. Point out the correct statement :
a) The only way to exit a repeat loop is to call break
b) Infinite loops should generally be avoided
c) Control structures like if, while, and for allow you to control the flow of an R program
d) All of the mentioned

View Answer

Answer: d [Reason:] Control structures are primarily useful for writing programs; for commandline interactive work.

3. _________ initiates an infinite loop right from the start.
a) never
b) repeat
c) break
d) set

View Answer

Answer: b [Reason:] These are not commonly used in statistical or data analysis applications but they do have their uses.

4. Which of the following code snippet stops loop after 20 iterations ?
a)

for(i in 1:100) {
      print(i)
              if(i > 20) {
               break 
       } 
}

b)

for(i in 1:100) {
      print(i)
              if(i > 19) {
               break 
       } 
}

c)

for(i in 1:100) {
      print(i)
              if(i < 20) {
               break 
       } 
}

d) All of the mentioned

View Answer

Answer: a [Reason:] break is used to exit a loop immediately, regardless of what iteration the loop may be on.

5. Point out the wrong statement :
a) Statements cannot be grouped together using braces ‘{’ and ‘}’
b) Computation in R consists of sequentially evaluating statements
c) Single statements are evaluated when a new line is typed at the end of the syntactically complete statement
d) None of the mentioned

View Answer

Answer: a [Reason:] Blocks are not evaluated until a new line is entered after the closing brace.

6. _______ is used to skip an iteration of a loop.
a) next
b) skip
c) group
d) all of the mentioned

View Answer

Answer: a [Reason:] No statement below next in the current loop is evaluated.

7. Which of the following code can be used to avoid numeric problems such as taking the logarithm of a negative number ?
a)

 if( any(x < 0) ) y <- log(1+x) else y <- log(x)

b)

 if( any(x <= 0) ) y <- log(1+x) else y <- log(x)

c)

 if( any(x >= 0) ) y <- log(1+x) else y <- log(x)

d) All of the mentioned

View Answer

Answer: b [Reason:] The else clause is optional. The statement if(any(x <= 0)) x <- x[x <= 0] is valid.

8. R has ________ statements that provide explicit looping.
a) two
b) three
c) four
d) all of the mentioned

View Answer

Answer: b [Reason:] They are for, while and repeat.

9. The syntax of the repeat loop is :
a) rep statement
b) repeat statement
c) repeat else
d) none of the mentioned

View Answer

Answer: b [Reason:] The repeat statement causes repeated evaluation of the body until a break is specifically requested.

10. Which will be the output of following code ?

> x <- 3
> switch(x, 2+2, mean(1:10), rnorm(5))

a) 2.2903605 2.3271663 -0.7060073 1.3622045 -0.2892720
b) 5.5
c) NULL
d) All of the mentioned

View Answer

Answer: a [Reason:] Conditions are always evaluated from left to right.

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