String Processing
Conditionals
In this lesson the student will learn how to:
- Use if-elsif-else constructs
- Use unless construct
- Use if after statement
- Use or construct
By the end of this lesson the student will be able to:
Write a simple quiz script for the amino acid
names and symbols.
Amino Acid Symbols
Here are the amino acid symbols:
@symbols = ('S', 'F', 'L', 'Y', 'C', 'W',
'P', 'H', 'Q', 'R', 'I', 'M',
'T', 'N', 'K', 'V', 'A', 'D',
'E', 'G' );
Here are the corresponding names:
@names = ("serine", "phenylalanine", "leucine", "tyrosine", "cysteine",
"tryptophan", "proline", "histidine", "glutamine", "arginine",
"isoleucine", "methionine", "threonine", "asparagine", "lysine",
"valine", "alanine", "aspartic acid", "glutamic acid", "glycine");
You will notice that most of the symbols and names start with the same
letter. However, since, for instance, there are three amino acid names which
begin with t (tyrosine, tryptophan, threonine), it is necessary to use other
letters. Why tryptophan got W as it's symbol is not immediately obvious. The
letters Q for glutamine and K for lysine also seem sort of arbitrary, but if
you inspect the symbols and names carefully you may discover how the symbols
were paired with the names.
There are other amino acids other than these which are coded for by the
genetic code. For instance, you may have heard of creatine,
carnitine or taurine which
are sometimes used as dietary supplements. Most of the 20 amino acids used
in the genetic code are also available as dietary supplements. One notable
exception is tryptophan which was available as a dietary supplement until a
food poisoning problem occured in the late 1980's.
<![CDATA[
#!/usr/bin/perl
@things = ( 5, "CA", 1, 10, "thing", 2, 7);
foreach $x (@things){
print "$x: ";
if($x =~ /\D+/){
print "not a number\n";
}
elsif($x>5) {
print "number greater than five\n";
}
elsif($x==5){
print "number equal to five\n";
}
elsif($x<5){
print "number less than five\n";
}
else{
print "unknown thing\n";
}
}
]]>
The following program shows examples of how to use the unless, if, and or
constructs.
<![CDATA[
#!/usr/bin/perl
@a = (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16);
print "UNLESS:\n";
foreach $item (@a){
print "$item is EVEN\n" unless ($item%2==1);
}
print "IF:\n";
foreach $item (@a){
print "$item is EVEN\n" if ($item%2==0);
}
sub check_item{
($i) = @_;
if($i%2==0){
return 0;
}
else{
return 1;
}
}
print "OR:\n";
foreach $item (@a){
check_item($item) or print "$item is EVEN\n";
}
]]>
Inspect the or example carefully. Notice that the check_item subroutine
returns either 0 or 1.
ASSIGNMENT:
Modify the following code according to the specifications which follow:
<![CDATA[
#!/usr/bin/perl
@symbols = ('S', 'F', 'L', 'Y', 'C', 'W',
'P', 'H', 'Q', 'R', 'I', 'M',
'T', 'N', 'K', 'V', 'A', 'D',
'E', 'G' );
@names = ("serine", "phenylalanine", "leucine", "tyrosine", "cysteine",
"tryptophan", "proline", "histidine", "glutamine", "arginine",
"isoleucine", "methionine", "threonine", "asparagine", "lysine",
"valine", "alanine", "aspartic acid", "glutamic acid", "glycine");
$cnt = 0;
$right = 0;
foreach $item (@symbols){
print "Symbol: $item\n";
print "Name: ";
$user = <STDIN>;
chomp($user);
if($user eq $names[$cnt]){
print "correct\n";
$right++;
}
else{
print "wrong\n";
}
$cnt++;
}
print "RESULTS: $right correct out of 20\n";
]]>
- figure out a way to use an or construct in place of the if-else
construct used in the foreach loop
- figure out a way to present the symbols in random order and still have
the checking mechanism work correctly
- report to the user a list of the symbol and name of the items missed during the
quiz