Part I Getting Started in VS .NET

Make QR Code 2d barcode in VS .NET Part I Getting Started

Part I Getting Started
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Condition Statement
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if (
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redCountingUP
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) redIntensity++;
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FIGURE 2-9 The if cond t on n act on
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If the condition is true (that is, the variable redCountingUp holds the value true in this case), the statement following the condition is performed. The result is that when this statement is obeyed, the value of redIntensity gets bigger if the program is counting up. The condition can be any value that gives a Boolean result, including this rather stupid code:
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if (true) redIntensity++;
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The preceding code is completely legal C# code and compiles with no problem. When the program runs, the condition is true, and the statement increases the red intensity value. This is very stupid code, though, as the test might as well not be there. You could also write the following:
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if (false) redIntensity++;
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In this code, the statement following the condition is never obeyed because the condition is always false. This C# code compiles all right, but if you look very closely at the Microsoft Visual Studio display, you might notice that it is trying to tell you something, as shown in Figure 2-10.
FIGURE 2-10 Comp er warn ngs.
If the error window in Figure 2-10 is not displayed, you can open it by selecting the View menu and clicking Error List in that menu. Alternatively you can use the key combination Ctrl+W+E. When the compiler has finished trying to convert your C# source code into a program that can be run on the computer, it tells you how many mistakes that it thinks it has found. There are two kinds of mistakes. An error is a mistake that prevents what you have written from being made into a program. Errors are really bad things like spelling identifiers wrong, using the wrong kind of brackets, and the like.
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The other kind of mistake is called a warning. This is where the compiler thinks you might have done something wrong, but it does not prevent your program from running. Figure 2-10 shows the warning message for a program with a test for (false) in it. What the compiler is telling you is that it has managed to work out that the statement after the test will never be reached. This is because it is impossible for the value false to be true. The compiler is warning you that although the code is legal C# code, what it does might actually not be what you want. The Great Programmer Speaks: Warnings Should Always Be Heeded Our Great
Programmer has very strong op n ons on comp er warn ngs; she reckons that your code shou d comp e w th no warn ngs at a Warn ngs usua y mean that your so ut on s mperfect n some way, and you shou d a ways take steps to nvest gate and reso ve them
Adding an Else Part
The condition you have created is only half correct. If the program is not counting up, it must make the value of redIntensity smaller. You can use the -- operator to do this, but we need to add extra code to the condition. You need to add an else part. Figure 2-11 shows another form of the if condition, with the else part added.
Condition Statement Performed if true Statement Performed if false
(redCountingUP)
redIntensity++;
else
redIntensity-- ;
FIGURE 2-11 The if cond t on w th an else part
The two statements are separated by a new key word, else. The new code means that if the program is counting up (that is, redCountingUp is true), the value gets bigger, but if the program is counting down (that is, redCountingUp is false), the value gets smaller. The else part is optional; you must add one only if you need it.
Testing Values
The program must also manage the value in redCountingUp so that when it reaches the upper limit, it starts to count down, and when it reaches the lower limit, it starts to count up again. In other words: 1. When redIntensity reaches 255, set redCountingUp to false. 2. When redIntensity reaches 0, set redCountingUp to true.
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