qr code generator with c# A Closer Look at Methods and Classes in Visual C#

Print QR-Code in Visual C# A Closer Look at Methods and Classes

A Closer Look at Methods and Classes
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int a = 15, b = 20; ConsoleWriteLine("a and b before call: " + a + " " + b); obNoChange(a, b); ConsoleWriteLine("a and b after call: " + a + " " + b); } }
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The output from this program is shown here:
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a and b before call: 15 20 a and b after call: 15 20
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As you can see, the operations that occur inside NoChange( ) have no effect on the values of a and b used in the call Again, this is because copies of the value of a and b have been given to parameters i and j, but a and b are otherwise completely independent of i and j Thus, assigning i a new value will not affect a When you pass a reference to a method, the situation is a bit more complicated In this case, the reference, itself, is still passed by value Thus, a copy of the reference is made and changes to the parameter will not affect the argument (For example, making the parameter refer to a new object will not change the object to which the argument refers) However and this is a big however changes made to the object being referred to by the parameter will affect the object referred to by the argument Let s see why Recall that when you create a variable of a class type, you are only creating a reference to an object Thus, when you pass this reference to a method, the parameter that receives it will refer to the same object as that referred to by the argument Therefore, the argument and the parameter will both refer to the same object This means that objects are passed to methods by what is effectively call-by-reference Thus, changes to the object inside the method do affect the object used as an argument For example, consider the following program:
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// Objects are passed by reference using System; class Test { public int a, b; public Test(int i, int j) { a = i; b = j; } /* Pass an object Now, oba and obb in object used in the call will be changed */ public void Change(Test ob) { oba = oba + obb; obb = -obb; } }
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Part I:
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class CallByRef { static void Main() { Test ob = new Test(15, 20); ConsoleWriteLine("oba and obb before call: " + oba + " " + obb); obChange(ob); ConsoleWriteLine("oba and obb after call: " + oba + " " + obb); } }
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This program generates the following output:
oba and obb before call: 15 20 oba and obb after call: 35 -20
As you can see, in this case, the actions inside Change( ) have affected the object used as an argument To review: When a reference is passed to a method, the reference itself is passed by use of call-by-value Thus, a copy of that reference is made However, the copy of that reference will still refer to the same object as its corresponding argument This means that objects are implicitly passed using call-by-reference
Use ref and out Parameters
As just explained, value types, such as int or char, are passed by value to a method This means that changes to the parameter that receives a value type will not affect the actual argument used in the call You can, however, alter this behavior Through the use of the ref and out keywords, it is possible to pass any of the value types by reference Doing so allows a method to alter the argument used in the call Before going into the mechanics of using ref and out, it is useful to understand why you might want to pass a value type by reference In general, there are two reasons: to allow a method to alter the contents of its arguments or to allow a method to return more than one value Let s look at each reason in detail Often you will want a method to be able to operate on the actual arguments that are passed to it The quintessential example of this is a Swap( ) method that exchanges the values of its two arguments Since value types are passed by value, it is not possible to write a method that swaps the value of two ints, for example, using C# s default call-by-value parameter passing mechanism The ref modifier solves this problem As you know, a return statement enables a method to return a value to its caller However, a method can return only one value each time it is called What if you need to return two or more pieces of information For example, what if you want to create a method that decomposes a floating-point number into its integer and fractional parts To do this requires that two pieces of information be returned: the integer portion and the fractional component This method cannot be written using only a single return value The out modifier solves this problem
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