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New page: In the previous chapter we looked at some basic conditional structures using the ''if ... else'' and ''if .. elsif ...'' mechanisms. These approaches to building conditional logic work wel...
In the previous chapter we looked at some basic conditional structures using the ''if ... else'' and ''if .. elsif ...'' mechanisms. These approaches to building conditional logic work well if you need to check a value against a only few different criteria (for example checking the value of a string against a couple of possible candidates):
<pre>
if customerName == "Fred"
print "Hello Fred!"
elsif customerName == "John"
print "Hello John!"
elsif customername == "Robert"
print "Hello Bob!"
end
</pre>
This can quickly become cumbersome, however, when a need arises to evaluate a large number of conditions. A much easier way to handle such situations is to use the Ruby ''case'' statement, the syntax for which is defined as follows:
''result'' = case ''value''
when ''match1'': ''result1''
when ''match2'': ''result2'
when ''match3'': ''result3'
when ''match4'': ''result4'
when ''match5'': ''result5'
when ''match6'': ''result6'
else ''match7'': ''result7'
end
</pre>
There can be any number of ''when'' statements - basically as many as you need to fully compare the ''value'' in the ''case'' statement against the possible options (represented by ''match1'' through to ''match7'' in the above example) specified by the ''when'' statements. When a match is found the result is assigned to ''result''.
Finally, The ''else'' statement specifies the default result to be returned if no match is found.
This concept is, perhaps, best explained using an example. The following Ruby case statement is designed to match a particular car model with a manufacturer. Once a match is found, the car and associated manufacturer are included in an output string:
<pre>
car = "Patriot"
manufacturer = case car
when "Focus": "Ford"
when "Navigator": "Lincoln"
when "Camry": "Toyota"
when "Civic": "Honda"
when "Patriot": "Jeep"
when "Jetta": "VW"
when "Ceyene": "Porsche"
when "Outback": "Subaru"
when "520i": "BMW"
when "Tundra": "Nissan"
else "Unknown"
end
puts "The " + car + " is made by " + manufacturer
</pre>
When executed, the resulting output will read:
<pre>
The Patriot is made by Jeep
</pre>
If no match was found in the case statement, then the default result, defined by the ''else'' statement would cause the following output to be generated:
<pre>
The Prius is made by Unknown
</pre>
<pre>
if customerName == "Fred"
print "Hello Fred!"
elsif customerName == "John"
print "Hello John!"
elsif customername == "Robert"
print "Hello Bob!"
end
</pre>
This can quickly become cumbersome, however, when a need arises to evaluate a large number of conditions. A much easier way to handle such situations is to use the Ruby ''case'' statement, the syntax for which is defined as follows:
''result'' = case ''value''
when ''match1'': ''result1''
when ''match2'': ''result2'
when ''match3'': ''result3'
when ''match4'': ''result4'
when ''match5'': ''result5'
when ''match6'': ''result6'
else ''match7'': ''result7'
end
</pre>
There can be any number of ''when'' statements - basically as many as you need to fully compare the ''value'' in the ''case'' statement against the possible options (represented by ''match1'' through to ''match7'' in the above example) specified by the ''when'' statements. When a match is found the result is assigned to ''result''.
Finally, The ''else'' statement specifies the default result to be returned if no match is found.
This concept is, perhaps, best explained using an example. The following Ruby case statement is designed to match a particular car model with a manufacturer. Once a match is found, the car and associated manufacturer are included in an output string:
<pre>
car = "Patriot"
manufacturer = case car
when "Focus": "Ford"
when "Navigator": "Lincoln"
when "Camry": "Toyota"
when "Civic": "Honda"
when "Patriot": "Jeep"
when "Jetta": "VW"
when "Ceyene": "Porsche"
when "Outback": "Subaru"
when "520i": "BMW"
when "Tundra": "Nissan"
else "Unknown"
end
puts "The " + car + " is made by " + manufacturer
</pre>
When executed, the resulting output will read:
<pre>
The Patriot is made by Jeep
</pre>
If no match was found in the case statement, then the default result, defined by the ''else'' statement would cause the following output to be generated:
<pre>
The Prius is made by Unknown
</pre>
