how to generate barcode in c# net with example retrieving Keys in Visual C#

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retrieving Keys
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Sometimes you might not be interested in the values within a hash, but want to get a feel for what the hash contains. A great way to do this is to look at the keys. Ruby gives you an easy way to see the keys in any hash immediately, using the keys method: x = { "a" => 1, "b" => 2, "c" => 3 } p x.keys
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["a", "b", "c"] keys returns an array of all the keys in the hash, and if you re ever in the mood, values will return an array of all the values in the hash, too. Generally, however, you ll look up values based on a key.
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Deleting hash elements is easy with the delete method. All you do is pass in a key as a parameter, and the element is removed: x = { "a" => 1, "b" => 2 } x.delete("a") p x
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{"b"=>2}
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Let s say you want to delete any hash elements whose value is below a certain figure. Here s an example of how to do this: x = { "a" => 100, "b" => 20 } x.delete_if { |key, value| value < 25 } p x
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{"a"=>100}
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It s possible to have hashes (or, indeed, any sort of object) within hashes, and even arrays within hashes, within hashes! Because everything is an object and hashes and arrays can contain any other objects, there exists the ability to create giant tree structures with hashes and arrays. Here s a demonstration:
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C ha p ter 3 r U B Y S B U ILDI NG B LO C K S : D a t a , e X p r e S S I O N S , a N D F LO W C O N t r O L
people = { 'fred' => { 'name' => 'Fred Elliott', 'age' => 63, 'gender' => 'male', 'favorite painters' => ['Monet', 'Constable', 'Da Vinci'] }, 'janet' => { 'name' => 'Janet S Porter', 'age' => 55, 'gender' => 'female' } } puts people['fred']['age'] puts people['janet']['gender'] p people['janet']
63 female {"name"=>"Janet S Porter", "gender"=>"female", "age"=>55} Although the structure of the hash looks a little confusing at first, it becomes reasonably easy when you break it down into sections. The 'fred' and 'janet' sections are simple hashes of their own, but they re wrapped up into another giant hash assigned to people. In the code that queries the giant hash, you simply chain the lookups on top of each other, as with puts people['fred']['age']. First it gets people['fred'], which returns Fred s hash, and then you request ['age'] from that, yielding the result of 63. Even the array embedded within Fred s hash is easy to access: puts people['fred']['favorite painters'].length puts people['fred']['favorite painters'].join(", ")
3 Monet, Constable, Da Vinci These techniques are used more and explained in greater depth in following chapters.
Flow Control
In this chapter, you ve used comparisons, together with if and unless, to perform different operations based upon the circumstances. if and unless work well on single lines of code, but when combined with large sections of code, they become even more powerful. In this section, you ll be looking at how Ruby lets you control the flow of your programs with these and other constructs.
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Ch apt er 3 rUB Y S B U IL DING B L OC K S : Da t a , e X p r e S S I O N S , a N D F LO W C O N t r O L
if and unless
The first use of if within this chapter used this demonstration: age = 10 puts "You're too young to use this system" if age < 18 If the value of age is under 18, the string is printed to the screen. The following code is equivalent: age = 10 if age < 18 puts "You're too young to use this system" end It looks similar, but the code to be executed if the expression is true is contained between the if expression and end, instead of the if expression being added onto the end of a single line of code. This construction makes it possible to put any number of lines of code in between the if statement and the end line: age = 10 if age < 18 puts "You're too young to use this system" puts "So we're going to exit your program now" exit end It s worth noting that unless can work in exactly the same way because unless is just the opposite of if: age = 10 unless age >= 18 puts "You're too young to use this system" puts "So we're going to exit your program now" exit end It s possible to nest logic, too, as in this example: age = 19 if age < 21 puts "You can't drink in most of the United States" if age >= 18 puts "But you can in the United Kingdom!" end end if and unless also supply the else condition, used to delimit lines of code that you want to be executed if the main expression is false:
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