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Workshop

 
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Workshop

Quiz

Examine the following block of code:


sub bar {

    ($a,$b)=@_;

    $b=100;

    $a=$a+1;

}

sub foo {

    my($a)=67;

    local($b)=@_;

    bar($a, $b);

}

foo(5,10)


1:

After you run bar($a, $b), what is the value in $b?

  1. 5

  2. 100

  3. 68

2:

What is the return value from foo()?

  1. 67

  2. 68

  3. undef

3:

Inside foo(), how is $b scoped?

  1. Lexically

  2. Dynamically

  3. Globally

Answers

A1:

b. $b is declared with local in foo() so that every called subroutine shares the same value for $b (unless they later declare $b again with local or my). After calling bar(), where $b is modified, $b is set to 100.

A2:

b. Surprised? The last statement in foo() is bar($a, $b). bar() returns 68 because the value of $a is passed to bar(), and it's incremented. foo() returns the value of the last expression, which is 68.

A3:

b. Variables declared with local are called dynamically scoped variables.

Activities

  • Use the functions from the statistics exercise in this hour and the word-counting code from Hour 7, "Hashes," to examine the length of the words in a document. Compute their mean, median, and standard deviation.

  • Write a function to print part of the Fibonacci series. This series begins 0, 1, 1, 2, 3, 5, 8 and continues forever. The Fibonacci series is a recurring pattern in mathematics and nature. Each successive number is the sum of the previous two (except 0 and 1). These numbers can be computed iteratively or recursively.

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