Creating an Array in .NET

Creating QR Code in .NET Creating an Array

Creating an Array
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What you need is a way of working through a list of scores using your program. In C#, a variable that holds a list of values is called an array. The type of values that you want your array to hold are integers, and it is one-dimensional, in that it has only one list of values. Arrays can be declared and initialized just like any other C# variable:
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int[] scores = new int[4];
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This declares an array variable called scores that can refer to one-dimensional integer arrays and makes it refer to a new 4-element array instance. This would let the array hold the score values for the four buttons on gamepad 1. You can think of an array as a row of numbered boxes, each of which can hold a single value. A single box in an array is called an element. Figure 8-2 shows how this works. The size of the array is set when you create it. In the previous code, you made an array with four elements. If you want a different size, you simply change the 4 to a different number.
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8 Creating a Timer 0 scores[ ] 0 1 0 2 0 3 0
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FIGURE 8-2 An array reference and an array nstance
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Note You may have not ced that I m ta k ng about array nstances and that arrays are created
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us ng the key word new I have used these terms before when I was ta k ng about objects Th s means that arrays are mp emented n C# as objects, and you can ask them to do th ngs for you Later n th s chapter, you see how you can use array propert es and methods to make your fe eas er
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Using Data in an Array
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Now that you have your array, you need to be able to get a hold of individual elements. If you take a look at Figure 8-2 again, you see that each element has a number above it. This is called the subscript or index of that element in the array. You can regard a subscript as telling the computer how far down an array to go to get to the element that is required. In this respect, array elements are similar to house numbers on a street (except that no houses have the number zero). To use a particular element in an array, you simply give the subscript of the element that you want. The following code shows how this works. The value of the subscript is enclosed in square brackets:
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if (oldpad1.Buttons.A == ButtonState.Released && pad1.Buttons.A == ButtonState.Pressed && scores[0] == 0) { scores[0] = timer; }
This C# code works in the same way as the original code, except that it uses the first element in the array, scores[0], instead of a variable called ascore1. You can use scores[1] as bscore1, the score for the B button on gamepad 1 and so on. At this point, it doesn t seem that creating an array has made life much easier; you ve only found a quick way of declaring more than one variable. However, the real power comes when you use variables in your array subscripts, as follows:
for ( int i = 0; i < 4 ; i++ ) { scores[i] = 0; }
This is a for loop construction that takes the value of i from 0 to 3 (remember that when the value of i reaches 4, the test i less than 4 fails and the loop stops). The value of i is used as a subscript for the array access. This means that the first time around the loop, the statement
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will set scores[0] to zero. The next time around the loop, the assignment statement works on scores[1], and so on, up until the end of the array. This is how you d set the scores array elements to zero at the start of a game. Note The prev ous code uses an add t ona C# feature of the for oop that ets you dec are the
counter var ab e ( n th s case, a var ab e ca ed i) n the oop tse f Th s var ab e ex sts on y for the durat on of the oop, be ng oca to the for oop b ock The Great Programmer th nks th s s the r ght th ng to do here, as you need the var ab e on y for the durat on of the oop b ock
In this case, you want to work with only four elements, so the code doesn t look that much shorter than your original. However, if you needed to set 1,000 values, the code would contain the same statements, except that you d change the limit value so that i goes up to 999. Note If you have a m nd ke your younger brother, at th s po nt you be wonder ng what
wou d happen f you tr ed to use s y subscr pt va ues ke scores[101] Your younger brother wou d no doubt be hop ng that th s wou d cause the computer to crash or, better yet, a ow access to secret memory ocat ons The bor ng answer s that f you step outs de what are ca ed the bounds of an array, your program s stopped n ts tracks by an except on because th s s just not a owed to happen n a proper anguage ke C# Th s form of naught ness was not a ways detected n o der computers, however, and was once one of the standard ways that a v rus program cou d attack a system
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