asp.net barcode scanning TEACHING YOUR SCRIPT TO MAKE DECISIONS in Objective-C

Make QR Code JIS X 0510 in Objective-C TEACHING YOUR SCRIPT TO MAKE DECISIONS

CHAPTER 10 TEACHING YOUR SCRIPT TO MAKE DECISIONS
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Let s examine the preceding script. Lines 2, 3, and 4 set the inventory. Each type of drink is represented by a variable that indicates how many single servings are left in the bottle. Later, lines 6 through 17 contain the conditional statement block that determines your drink, or what the script calls my_drink. By the end of that conditional statement, the inventory has been updated to compensate for the drink you got. Lines 19 through 30 do the same thing, but this time the result assigns a drink value to the friend_drink variable.
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What instantly irritates me about the preceding script is that the two main chunks, lines 6 17 and lines 19 30, are nearly identical. This is wasteful coding and will simply not do! When you encounter two parts of your script that are similar, you usually can condense them and make one block take care of both tasks. The two main forms of doing this are subroutines and repeat loops (or a combination of both). I know we are getting slightly sidetracked here, but I just can t leave the poor script looking like that. So what I ll do is put the conditional statement into a subroutine and call it twice, as shown in Figure 10-4.
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Figure 10-4. The conditional statement appears only once but can be called multiple times.
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CHAPTER 10 TEACHING YOUR SCRIPT TO MAKE DECISIONS
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With a bit more thought, you can make the script handle parties of any size by creating a list of people you want to get drinks for and then looping through that list. Each loop will determine the drink for the next person in the list: property sodas_left : 4 property beers_left : 1 property vodkas_left : 5 set partygoers_names to {"Sue", "Jane", "Sarah", "Steve", "Hanaan", "Jon"} repeat with name_ref in partygoers_names display dialog name_ref & " is drinking " & get_drink() end repeat on get_drink() ... In a real-world situation, I would start by loading the inventory from a database (or user input) and then outputting the final inventory (in other words, after the drinks have been taken) at the end of the script.
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Clarifying Your Conditionals
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What s important to remember when working with conditional statements is that when the script runs, the expression that lies between the word if and the word then will be evaluated and reduced to one thing: a value that is either true or false. Although the Boolean result may be simple, the logic used to arrive at it may be complex. Until now you have seen a simple Boolean expression, sodas_left > 0, which simply evaluates one number. Figure 10-5 shows a complex Boolean expression used in the conditional statement.
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Figure 10-5. A conditional statement using a complex Boolean expression To make this situation a bit easier to swallow, what I usually do is start by assigning the result of the complex Boolean expression to a well-named variable. I can then use that variable in the conditional statement instead of the monstrous expression itself. Figure 10-6 shows an example of this.
CHAPTER 10 TEACHING YOUR SCRIPT TO MAKE DECISIONS
Figure 10-6. The same complex Boolean expression assigned to a variable before being used in a conditional statement
Nesting Conditional Statements
Another way to organize complex conditional code is by nesting several simple conditional blocks one inside another. You put forth one condition if it evaluates to true, the next condition is tested, and so on. Figure 10-7 shows a simple nested conditional statement.
Figure 10-7. A simple nested conditional statement By the nature of their functionality, some scripts will contain more conditional statements than others. Some scripts contain so many that their entire structure is one huge conditional statement. Another way to form complex conditional statements is to use small conditional statements and nest them in other conditional statements. It does make the script longer, but as the script as a whole becomes larger and more difficult to handle, you may see the benefits of this style of writing. Let s look at an example say you re in the market for a car. You travel from dealership to dealership and present your requirements in two different formats. The first format is this single statement: If you have a car that is yellow or green, gets more than 30 miles per gallon, can fit five, is less than three years old, and costs less than $10,000, I ll take it!
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