c# 2d data matrix Other Topics in Visual C#.NET

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Miscellaneous Topics Strings Parsing Strings to Data Values Nullable Types Method Main Documentation Comments Nested Types
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In this chapter, you will look at a number of other topics that are important in using C#, but that don t fit neatly into one of the other chapters. These include string handling, nullable types, the Main method, documentation comments, and nested types.
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Strings
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Zeros and ones are fine for internal computation, but for human readable input and output, we need strings of characters. The BCL provides a number of classes that make string handling easy. The C# predefined type string represents the .NET class System.String. The most important things to know about strings are the following: strings are arrays of Unicode characters. strings are immutable they cannot be changed. The string type has many useful string manipulation members. These allow you to determine the length of a string, concatenate strings, change the case of a string, and many other useful tasks. Some of the most useful members are listed in Table 23-1. Table 23-1. Useful Members of the string Type
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Length Concat Contains Format Insert Remove Replace SubString ToUpper ToLower
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Property Static method Method Static method Method Method Method Method Method Method
Meaning
Returns the length of the string Returns a string that is the concatenation of its argument strings Returns a bool value indicating whether the argument is a substring of the object string Returns a formatted string Inserts a string at a specific point in the object string Removes a set of characters from the object string Replaces a character or string in the object string Retrieves a substring from the object string Returns a copy of the object string where the alphabetic characters are all uppercase Returns a copy of the object string where the alphabetic characters are all lowercase
The names of many of the methods in Table 23-1 sound as if they are changing the string object. Actually, they are not changing the strings but returning new copies. For a string, any change allocates a new immutable string.
CHAPTER 23 OTHER TOPICS
For example, the following code declares and initializes a string called s. The first WriteLine statement calls the ToUpper method on s, which returns a copy of the string that is in all uppercase. The last line prints out the value of s, showing that it is unchanged. string s = "Hi there."; Console.WriteLine("{0}", s.ToUpper()); Console.WriteLine("{0}", s); This code produces the following output: HI THERE. Hi there. // Print uppercase copy. // String is unchanged.
Using Class StringBuilder
The StringBuilder class produces strings that can be changed. The StringBuilder class is a member of the BCL, in namespace System.Text. A StringBuilder object is a mutable array of Unicode characters. For example, the following code declares and initializes a string of type StringBuilder and prints its value. The fourth line changes the actual object by replacing part of the string. Now, when you print the value of the string, you can see that, unlike an object of type string, the StringBuilder object has actually been changed. using System.Text; StringBuilder sb = new StringBuilder("Hi there."); Console.WriteLine("{0}", sb); // Print string. sb.Replace("Hi", "Hello"); // Replace a substring. Console.WriteLine("{0}", sb); // Print changed string. This code produces the following output: Hi there. Hello there. When a StringBuilder object is created, the class allocates a buffer longer than the actual current string length. As long as the changes made to the string can fit in the buffer, no new memory is allocated. If changes to the string require more space than is available in the buffer, a new, larger buffer is allocated, and the string is copied to it. Like the original buffer, this new buffer also has extra space.
CHAPTER 23 OTHER TOPICS
Formatting Numeric Strings
Throughout the text, I have used the WriteLine method to display values. Each time, I used the simple substitution marker consisting of curly braces surrounding an integer. Many times, however, you will want to present the output of a text string in a format more appropriate than just a plain number. For example, you might want to display a value as currency, or as a fixedpoint value with a certain number of decimal places. You can do this by using format strings. For example, the following code consists of two statements that print out the value 500. The first line prints out the number without any additional formatting. In the second line, the format string specifies that the number should be formatted as currency. Console.WriteLine("The value: {0}." , 500); Console.WriteLine("The value: {0:C}.", 500); Format as currency. This code produces the following output. The value: 500. The value: $500.00. The difference between the two statements is that the format item includes additional information in the form of a format specifier. The syntax for a format specifier consists of three fields inside the set of curly braces: the index, the alignment specifier, and the format specifier. The syntax is shown in Figure 23-1. // Print out number. // Format as currency.
Figure 23-1. Syntax for a format item The first thing in the format item is the index. As you well know by now, the index specifies which item from the list, following the format string, should be formatted. The index is required, and numbering of the list items starts at 0.
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