215: Working with Strings in C#.NET

Draw PDF 417 in C#.NET 215: Working with Strings
Listing 215: Working with Strings
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class Uppercase { static void Main() { string text, uppercase; SystemConsoleWrite("Enter text: "); text = SystemConsoleReadLine(); // Return a new string in uppercase uppercase = textToUpper(); SystemConsoleWriteLine(uppercase); } }
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null and void
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OUTPUT 213:
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Enter text: This is a test of the emergency broadcast system THIS IS A TEST OF THE EMERGENCY BROADCAST SYSTEM
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If the immutability of a string is ignored, mistakes similar to those shown in Listing 214 can occur with other string methods as well To actually change the value in text, assign the value from ToUpper() back into text, as in the following:
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text = textToUpper();
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SystemTextStringBuilder
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If considerable string modification is needed, such as when constructing a long string in multiple steps, you should use the data type SystemTextStringBuilder rather than string SystemTextStringBuilder includes methods such as Append(), AppendFormat(), Insert(), Remove(), and Replace(), some of which also appear on string The key difference, however, is that on SystemTextStringBuilder, these methods will modify the data in the variable, and will not simply return a new string
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null and void
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Two additional keywords relating to types are null and void null is a literal value used to indicate that the data type (specifically, a reference type) is assigned nothing void is used to indicate the absence of a type or the absence of any value altogether
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null
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null can also be used as a type of string literal null indicates that a vari-
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able is set to nothing Only reference types can be assigned the value null The only reference type covered so far in this book is string; 5 covers the topic of reference types in detail For now, suffice it to say that a reference type contains a pointer, an address, or a reference to a location in memory that is different from where the actual data resides Code that sets
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2: Data Types
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a variable to null explicitly assigns the reference to point at nothing In fact, it is even possible to check whether a reference type points to nothing Listing 216 demonstrates assigning null to a string variable
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Listing 216: Assigning null to a String
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static void Main() { string faxNumber; // // Clear the value of faxNumber faxNumber = null; // }
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It is important to note that assigning the value null to a reference type is distinct from not assigning it at all In other words, a variable that has been assigned null has still been set, and a variable with no assignment has not been set and therefore will likely cause a compile error if used prior to assignment Assigning the value null to a string is distinctly different from assigning an empty string, "" null indicates that the variable has no value "" indicates that there is a value: an empty string This type of distinction can be quite useful For example, the programming logic could interpret a faxNumber of null to mean that the fax number is unknown, whereas a faxNumber value of "" could indicate that there is no fax number
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The void Nontype Sometimes the C# syntax requires a data type to be specified but no data is passed For example, if no return from a method is needed, C# allows the use of void to be specified as the data type instead The declaration of Main within the HelloWorld program is an example Under these circumstances, the data type to specify is void The use of void as the return type indicates that the method is not returning any data and tells the compiler not to expect a value void is not a data type per se, but rather an identification of the fact that there is no data type
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null and void
Language Contrast: C++ void Is a Data Type
In C++, void is a data type commonly used as void** In C#, void is not considered a data type Rather, it is used to identify that a method does not return a value