Scalar Data Types and Basic IO

1
Scalar Data Types and Basic I/O
2
Variables in Perl

• You DO NOT have to declare variables in Perl.
• Unless you force it to force you to declare
  variables.
• Three basic types of variables
• Scalar
• Array
• Hashes

3
Scalars

• Scalar variables store single values.
• This single value can be any of the following
  types
• int, float, double, char, string, or references.
• In Perl these various types fall into one of
  three categories
• numbers, strings, and references.
• You dont have to declare a variables type.

4
Scalars Declaration

• All scalar variables begin with a .
• is NOT part of the variable!
• Next character is either a letter or _.
• Remaining characters are a mix of letters,
  numbers, and _.
• Correct x, myvar123, avg_height
• Wrong 2values, avg-height, goodday.

5
Scalars Numbers

• Unlike C/C, all numeric data in Perl are stored
  as double precision floating points.
• Ex 37 3.7 .37 37. 3E7 3e7 3E-7
• Hex 0x2aff, 0xAA3, 0XFFF
• Octal 077 0276
• Underscore 3_212_567 ? 3,212,567.
• Again, you do not need to specify the type.

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Numeric Operators
and have the highest precedence.
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Examples

• 4 2 ? 0
• 5 / 2 ? 2.5 (5 and 2 are coerced from integers to
  reals).
• total 3
• a 2
• b / c / 2
• Important. The order of evaluation of operands of
  operators is unspecified. This is left for the
  compiler to decide.
• Ex x x--

8
Scalars Strings

• Unlike C/C, strings in Perl are not terminated
  by \0.
• They are not represented as an array of
  characters.
• Individual characters cannot be accessed with
  .
• There are two types of strings in Perl
• Single quoted strings ().
• Double quoted strings ().

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Single Quoted Strings

• Strings delimited by (). They are not
  interpolated and cannot contain escape sequence
  characters.
• Examples
• hello
• Don\t do it!
• can\t, won\t, wouldn\t ever!
• apples are good\n

??
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Single Quoted Strings

• Another to say the same thing
• qhello
• qapples are good\t
• qDont do it!
• qcant, wont, wouldnt ever!
• Can also use ( ), , , for better
  readability
• Q(hello)
• Qcant, wont, wouldnt ever!

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Double Quoted Strings.

• Differs from single quoted strings in two ways
• Can include escape sequence characters e.g. \n,
  \t, \r, etc.
• Variables in the string are interpolated.
• Examples
• The man said, \Quantity \t Price \t Total\
  \n\n
• Apples are good for name. ? Apples are
  good for bob.
• Apples are good for \name. ? Apples are
  good for name.
• Today is dayday. ? Today is Monday.
• Can also use qq
• Ex qqNo way!, said the girl.

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When q Meets qq

• What happens when you put () and () together?
• If is embedded within
• The boy said, Today is day
• If is embedded within
• The boy said, Today is day

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String Operators

• String Catenation (.) Append two strings
  together.
• Happy . Birthday ? Happy Birthday.
• str . Holidays ? Happy Holidays.
• The operands are not effected by (.)
• Repetition operator (x)
• Beat OU! x 3 ? Beat OU! Beat OU! Beat OU!
• What about?
• Happy . Birthday! x 2

? Happy Birthday! Birthday!
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String Functions

• Perl provides several useful string manipulation
  functions.
• chop and chomp
• length, lc, uc
• ord, hex, oct
• index, rindex
• substr, join

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Chop and Chomp

• Chop removes the last character in a string.
• chop(apples) ? apple
• If a, b, and c are a, an, and ant, then
  chop(a, b, c) ? a an
• Chomp removes the ending input record separator
  (e.g. newline) in a string.
• If string does not end with an input record
  separator, then chomp does nothing to the string
  and returns 0.

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length, lc, and uc

• length returns the number of chars.
• Ex length(apples) ? 6
• lc converts a string to all lower case.
• Ex lc(ApPlEs) ? apples
• uc converts a string to all upper case.
• Ex uc(apples) ? APPLES

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index and rindex

• index searches for the starting position of a
  substring.
• rindex same as index except search is done from
  right to left.
• Examples
• index(apples, pp) returns 1
• rindex(apples, pp) returns 1
• index(apples, p) returns 1
• rindex(apples, p) returns 2
• index(apples, q) returns -1

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substr

• substr extracts a substring
• The way to call it is
• substr(string, position, length)
• Examples
• substr(fruit juice, 0, 3) returns fru
• substr(fruit juice, 3, 5) returns it ju
• substr(fruit juice, -3, 3) returns

ice
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join

• Like (.) but appends several strings separated by
  a deliminator.
• The way to call it is
• join Expression, List
• Example month 09, day 01, year 05
• join /, month, day, year ? 09/01/05.
• join /, month, day, 2005 ? ??

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Mixed Modes

• What happens when strings and numbers interact?
• The output depends on the context.
• Examples str 32abc
• 7 str
• 7 . str
• What if str abc32
• 7 str
• 7 . str

? 39
? 732abc
? 7
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Assignments

• Simple assignment operators ()
• x 2
• average sum / total
• x y b 2
• result 17 (sum x y)
• chomp(str str1. str1)
• Compound assignment operators ()
• sum new_value
• str . ing
• result 4

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Basic I/O

• reads input from a keyboard
• new_input
• print writes output to screen
• print Hello world!\n
• print (Was summer vacation fun?\n)
• print (The sum is sum, \tThe
  average is average\)

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A Simple Example
circle Input The radius of a circle.
Output The area and circumference of the
circle. pi 3.14 print Please enter the
radius of the circle radius area
pi radius radius circumference pi
2 radius print A circle of radius radius
has an area of area \n, and a
circumference of circumference \n