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Interpolation

Variables occuring within a double quoted string are 'interpolated'. 

$x = 4;
$name = "Joe";

print "I am $name. I am $n years old.\n";
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Very convenient.

Dollar Sign ($) is special.
To get an actual dollar sign: \$
To get an actual backslash: \\

SINGLE quoted strings take their contents literally - no interpolation, no backslash interpretation.
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At Sign (@) is special, too - more on this later.

Concatenation and Replication

There are two simple string operators: '.' and 'x' - dot/period and lower case x. 

$full = $first . " " . $last;       # concatenated
Interpolation often works better than concatenation: 

$full = "$first $last";
The x operator replicates the string n times. It is not used often but is very convenient to have when you need it. 

$divider = "-" x 40;
$greet = "hello ";
$n = 5;
print $greet x $n;
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Reading from the keyboard


print "Name? ";         # note - no newline here
$name = <STDIN>;
STDIN must be capitalized.
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This gets a line from the terminal keyboard up to a newline (Enter or Return). Note that the newline (\n) IS included at the end of the receiving variable. 


print "Your name is $name.  Hello!\n";
This prints (Try it!) the following: 

Your name is Joe
.  Hello!
This is not quite what you expect or want.

Chopping and Chomping

The function 'chop' will remove the last character from $name regardless of what it is. 

chop $name;
The kinder and gentler 'chomp' will remove one newline at the end of $name. If the last character is not a newline it will have no effect at all. 

chomp $name;
Now we can rewrite the reading of the name from the keyboard like so: 

print "Name? ";
$name = <STDIN>;
chomp $name;
print "Your name is $name.  Hello!\n";
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Integer/String Conversion


$n = "34";
print $n*3;           # 102

$n = 34;
print "hello" . $n;   # hello34

print 123 x "3";      # 123123123
Perl will generally do what you want and expect it will do.
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Exercises

  1. Redo the first exercise in the previous section using the new ideas presented here. Ask for the number rather than 'hard-coding' it in your program. Use string interpolation for output. Put a dividing line between the parts of the output.

  2. Quadratic polynomials:
    have two solutions which can be found with the quadratic formula:
    You may remember this from your days in high school algebra.

    For example: 

    
x**2 -5x + 6 = 0
    This polynomial has two solutions: 2 and 3. Can you compute them by hand using the formula above? In this case a = 1, b = -5 and c = 6.

    Perl has a square root function which takes one parameter: 

    
$x = sqrt 144;
print "$x\n";      # 12
    Ask for values for a, b and c. Compute and then print out the two solutions. Note that some quadratic equations will have complex numbers as a solution (when the value (underneath the square root is negative). We'll deal with these soon. For now, just try these values for a, b, and c: 
    
a    1
b    7
c   12

a    6
b   -5
c   -4

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