The String class provides a lot of useful methods for manipulating strings. For example, the EndsWith method returns True if a string ends with a particular substring. The following code determines whether a string ends with the substring dog:

Dim str As String = "The quick brown fox jumps over the lazy dog"
MessageBox.Show("Ends with dog: " & str.EndsWith("dog"))

Table 14-1 summarizes the String class's most useful methods.

In addition to all of these methods, the String class provides a very useful Length property. As you can probably guess, Length returns the number of characters in the string.

The String class also provides the useful shared methods Format and Join. A shared method is one that is provided by the class itself rather than an instance of the class. You invoke a static method using the class's name instead of a variable's name.

The Format method formats a series of parameters according to a format string and returns a new string. For example, the following code uses the String class's Format method to display the values in the variables x and y surrounded by parentheses and separated by a comma:

Dim x As Integer = 10
Dim y As Integer = 20
Dim txt As String = String.Format("({0}, {1})", x, y)
MessageBox.Show(txt)

The next section says more about the Format method.

The Join method does the opposite of the Split method: it joins a series of strings, separating them with a delimiter.

The String class's Format method builds a formatted String. Its first parameter is a format string that tells how the method should display its other parameters. The format string can contain literal characters that are displayed as they appear, plus formatting fields.

Each field has the following syntax:

{index[,alignment][:formatString]}

The curly braces are required. The square brackets indicate optional pieces.

The key pieces of the field are:

For example, the following code defines a String and two Decimal values. It then displays the result in a message box.

Dim itemName As String = "Fiendishly Difficult Puzzles"
Dim quantity As Decimal = 2D
Dim price_each As Decimal = 9.99D

MessageBox.Show(
    String.Format("You just bought {1} {0} at {2:C} each.",
    itemName, quantity, price_each))

The format string is "You just bought {1} {0} at {2:C} each."

The first field is {1}. This displays parameter number 1 (the second parameter — remember they're zero-based).

The second field is {0}. This displays the first parameter.

The third field is {2:C}. This displays the third parameter with the format string C, which formats the value as currency.

The result is:

You just bought 2 Fiendishly Difficult Puzzles at $9.99 each.

The following code shows an example that uses field widths to make values line up in columns. Before the code executes, assume that itemName1, quantity1, and the other variables have already been initialized. (The Console.WriteLine statement writes output into the Output window.)

Console.WriteLine(
    String.Format("{0,-20}{1,5}{2,10}{3,10}",
    "Item", "Qty", "Each", "Total")
)
Console.WriteLine(
    String.Format("{0,-20}{1,5}{2,10:C}{3,10:C}",
    itemName1, quantity1, priceEach1, quantity1 * priceEach1)
)
Console.WriteLine(
    String.Format("{0,-20}{1,5}{2,10:C}{3,10:C}",
    itemName2, quantity2, priceEach2, quantity2 * priceEach2)
)
Console.WriteLine(
    String.Format("{0,-20}{1,5}{2,10:C}{3,10:C}",
    itemName3, quantity3, priceEach3, quantity3 * priceEach3)
)

Notice that the code begins with a line that defines the column headers. Its formatting string uses the same indexes and alignment values as the other formatting strings so the headers line up with the values below.

The following shows the result:

Item                  Qty      Each     Total
Pretzels (dozen)        4     $5.95    $23.80
Blue laser pointer      1   $149.99   $149.99
Titanium spork          2     $8.99    $17.98

Every object provides a ToString method that converts the object into a string. For simple data types such as numbers and dates, the result is the value in an easy-to-read string.

The ToString method for some objects can take a format parameter that tells how you want the item formatted. For example, the following statement displays the variable cost formatted as a currency value in the Output window:

Console.WriteLine(cost.ToString("C"))

The following sections describe standard and custom format strings for numbers, dates, and times. You can use these as arguments to the ToString method or as format strings passed to String.Format.

In this Try It, you build a program that displays the current date and time in a Label when it starts, as shown in Figure 14-1.

Figure 14.1. FIGURE 14-1