Strings in C#
In this part of the C# tutorial, we will work with string data in more detail.Strings are the most important data types in computer languages. That is why we dedicate a whole chapter to working with strings in C#.
A string is a sequence of characters. In C#, a string is a sequence of unicode characters. It is a data type which stores a sequence of data values, usually bytes, in which elements usually stand for characters according to a character encoding. When a string appears literally in source code, it is known as a string literal.
First example
In C# string literals are enclosed by double quotes.using System;In the preceding example, we create two string variables. Then we add them and compute the length of the first string.
public class CSharpApp
{
static void Main()
{
string str1 = "There are 10";
string str2 = " apples";
Console.WriteLine(str1 + str2);
Console.WriteLine("The length of the first string is "
+ str1.Length.ToString() + " characters");
}
}
string str1 = "There are 10";A string variable is declared and initiated.
Console.WriteLine(str1 + str2);Two strings are concatenated. We use the + operator to add two strings.
Console.WriteLine("The length of the first string is "
+ str1.Length.ToString() + " characters");
The Length property is used to determine the length of the string. $ ./basics.exeRunning the example gives this result.
There are 10 apples
The length of the first string is 12 characters
Using quotes
What if we wanted to display quotes, for example in a direct speech? In such a case, inner quotes must be escaped.using System;We use the (\) character to escape additional quotes.
public class CSharpApp
{
static void Main()
{
Console.WriteLine("There are many stars.");
Console.WriteLine("He said, \"Which one is your favourite?\"");
}
}
$ ./quotes.exeOutput.
There are many stars.
He said, "Which one is your favourite?"
Multiline strings
It is possible to create a multiline string in C#.using System;A multiline string can be created easily by using the (@) character at the beginning of the string.
public class CSharpApp
{
static void Main()
{
string multiString = @"I cheated myself
like I knew I would
I told ya, I was trouble
you know that I'm no good";
Console.WriteLine(multiString);
}
}
$ ./multiline.exe
I cheated myself
like I knew I would
I told ya, I was trouble
you know that I'm no good
Comparing strings
We can compare two strings with a (==) operator.using System;Comparing strings.
public class CSharpApp
{
static void Main()
{
Console.WriteLine("12" == "12");
Console.WriteLine("17" == "9");
Console.WriteLine("aa" == "ab");
}
}
$ ./compare.exeOutput of the program.
True
False
False
There is a
string.Compare() method, which compares two specified strings and returns an integer that indicates their relative position in the sort order. If the returned value is less than zero, the first string is less than the second. If it returns zero, both strings are equal. Finally, if the returned value is greater than zero, the first string is greater than the second. using System;There is an optional third ignoreCase argument, that determines, if the case should be honored or not.
public class CSharpApp
{
static void Main()
{
string str1 = "ZetCode";
string str2 = "zetcode";
Console.WriteLine(string.Compare(str1, str2, true));
Console.WriteLine(string.Compare(str1, str2, false));
}
}
Console.WriteLine(string.Compare(str1, str2, true));Compare two strings and ignore the case. This line prints 0 to the console.
String methods
C# has useful built-in methods that can be used for working with strings.The
Join() and Split()are very handy methods. using System;In our program, we will join and split strings.
public class CSharpApp
{
static void Main()
{
string[] items = new string[] {"C#", "Visual Basic",
"Java", "Perl"};
string langs = string.Join(",", items);
Console.WriteLine(langs);
string[] ls = langs.Split(',');
foreach (string lang in ls)
{
Console.WriteLine(lang);
}
}
}
string[] items = new string[] {"C#", "Visual Basic",
"Java", "Perl"};
This is an array of strings. These strings are going to be joined. string langs = string.Join(",", items);
All words from the array are joined. We build one string from them. There will be a comma character between each two words. string[] ls = langs.Split(',');
As a reverse operation, we split the langs string. The Split() method returns an array of words, delimited by a character. In our case it is a comma character. foreach (string lang in ls)We go through the array and print its elements.
{
Console.WriteLine(lang);
}
$ ./joinsplit.exeOutput of the example.
C#,Visual Basic,Java,Perl
C#
Visual Basic
Java
Perl
using System;We introduce five string methods in the above example.
public class CSharpApp
{
static void Main()
{
string str = "Determination";
Console.WriteLine(str.Contains("e"));
Console.WriteLine(str.IndexOf("e"));
Console.WriteLine(str.LastIndexOf("i"));
Console.WriteLine(str.ToUpper());
Console.WriteLine(str.ToLower());
}
}
Console.WriteLine(str.Contains("e"));
The Contains() method returns True if the string contains a specific character. Console.WriteLine(str.IndexOf("e"));
The IndexOf() returns the first index of a letter in the string. Console.WriteLine(str.LastIndexOf("i"));
The LastIndexOf() methods returns the last index of a letter in a string. Console.WriteLine(str.ToUpper());Letters of the string are converted to uppercase with the
Console.WriteLine(str.ToLower());
ToUpper() method and to lowercase with the ToLower() method. $ ./strmethods.exeRunning the program.
True
1
10
DETERMINATION
determination
Copy vs Clone
We will describe a difference between two methods.Copy()and Clone(). The Copy() method creates a new instance of string with the same value as a specified string. The Clone() method returns a reference to the string, which is being cloned. It is not an independent copy of the string on the Heap. It is another reference on the same string. using System;Our example demonstrates the difference between the two methods.
public class CSharpApp
{
static void Main()
{
string str = "ZetCode";
string cloned = (string) str.Clone();
string copied = string.Copy(str);
Console.WriteLine(str.Equals(cloned)); // prints true
Console.WriteLine(str.Equals(copied)); // prints true
Console.WriteLine(ReferenceEquals(str, cloned)); // prints true
Console.WriteLine(ReferenceEquals(str, copied)); // prints false
}
}
string cloned = (string) str.Clone();The string value is cloned and copied.
string copied = string.Copy(str);
Console.WriteLine(str.Equals(cloned)); // prints trueThe
Console.WriteLine(str.Equals(copied)); // prints true
Equals() method determines whether two string objects have the same value. The contents of all three strings are the same. Console.WriteLine(ReferenceEquals(str, cloned)); // prints trueThe
Console.WriteLine(ReferenceEquals(str, copied)); // prints false
ReferenceEquals() method compares the two reference objects. Therefore comparing a copied string to the original string returns false. Because they are two distinct objects. Formatting strings
In the next examples, we will format strings. The .NET Framework has a feature called composite formatting. It is supported by Format() and WriteLine() methods. A method takes a list of objects and a composite format string as input. The format string consists of fixed string plus some format items. These format items are indexed placeholders which correspond to the objects in the list.The format item has the following syntax:
{index[,length][:formatString]}
The index component is mandatory. It is a number starting from 0 that refers to an item from the list of objects. Multiple items can refer to the same element of the list of objects. An object is ignored, if it is not referenced by a format item. If we refer outside the bounds of the list of objects, a runtime exception is thrown. The length component is optional. It is the minimum number of characters in the string representation of the parameter. If positive, the parameter is right-aligned; if negative, it is left-aligned. If it is specified, there must by a colon separating the index and the length.
The formatString is optional. It is a string that formats a value is a specific way. It can be used to format dates, times, numbers or enumerations.
Here we show, how to work with length component of the format items. We print three columns of numbers to the terminal. Left, middle and right aligned.
using System;We print a simple message to the console. We use only index component of the format item.
public class CSharpApp
{
static void Main()
{
int oranges = 2;
int apples = 4;
int bananas = 3;
string str1 = "There are {0} oranges, {1} apples and " +
"{2} bananas";
string str2 = "There are {1} oranges, {2} bananas and " +
"{0} apples";
Console.WriteLine(str1, oranges, apples, bananas);
Console.WriteLine(str2, apples, oranges, bananas);
}
}
string str1 = "There are {0} oranges, {1} apples and " +
"{2} bananas";
The {0}, {1}, and {2} are format items. We specify the index component. Other components are optional. Console.WriteLine(str1, oranges, apples, bananas);Now we put together the composite formatting. We have the string and the list of objects (oranges, apples, bananas). The {0} format item refers to the oranges. The
WriteLine() method replaces the {0} format item with the contents of the oranges variable. string str2 = "There are {1} oranges, {2} bananas and " +
"{0} apples";
The order of the format items referring to the objects is notation important. $ ./format1.exe
There are 2 oranges, 4 apples and 3 bananas
There are 2 oranges, 3 bananas and 4 apples
using System;We print numbers in a decimal and hexadecimal format. We also align the numbers using the length component.
public class CSharpApp
{
static void Main()
{
Console.WriteLine("{0} {1, 12}",
"Decimal", "Hexadecimal");
Console.WriteLine("{0:D} {1,8:X}",
502, 546);
Console.WriteLine("{0:D} {1,8:X}",
345, 765);
Console.WriteLine("{0:D} {1,8:X}",
320, 654);
Console.WriteLine("{0:D} {1,8:X}",
120, 834);
Console.WriteLine("{0:D} {1,8:X}",
620, 454);
}
}
Console.WriteLine("{0:D} {1,8:X}",
502, 546);
The {0:D} format item specifies, the first item from the list of supplied objects will be taken and formatted in the decimal format. The {1,8:X} format item takes the second item. Formats it in the hexadecimal format (:X). And the string length will be 8 characters (,8). Because the number has only three characters, it is right aligned and padded with empty strings. $ ./format2.exeRunning the example.
Decimal Hexadecimal
502 222
345 2FD
320 28E
120 342
620 1C6
The last two examples will format numeric and date data.
using System;The example demonstrates the standard formatting specifiers for numbers. Number 126 is printed in five different formats; normal, scientific, currency, percent and hexadecimal.
public class CSharpApp
{
static void Main()
{
Console.WriteLine(string.Format("Number: {0:N}", 126));
Console.WriteLine(string.Format("Scientific: {0:E}", 126));
Console.WriteLine(string.Format("Currency: {0:C}", 126));
Console.WriteLine(string.Format("Percent: {0:P}", 126));
Console.WriteLine(string.Format("Hexadecimal: {0:X}", 126));
}
}
$ ./format3.exeOutput.
Number: 126.00
Scientific: 1.260000E+002
Currency: $126.00
Percent: 12,600.00 %
Hexadecimal: 7E
Finally, we will format date and time data.
using System;The preceding example demonstrates the standard formatting specifiers for dates.
public class CSharpApp
{
public static void Main()
{
DateTime today = DateTime.Now;
Console.WriteLine(string.Format("Short date: {0:d}", today));
Console.WriteLine(string.Format("Long date: {0:D}", today));
Console.WriteLine(string.Format("Short time: {0:t}", today));
Console.WriteLine(string.Format("Long time: {0:T}", today));
Console.WriteLine(string.Format("Month: {0:M}", today));
Console.WriteLine(string.Format("Year: {0:Y}", today));
}
}
$ ./format4.exeOutput.
Short date: 4/11/2011
Long date: Monday, April 11, 2011
Short time: 11:14 AM
Long time: 11:14:54 AM
Month: April 11
Year: April, 2011
This part of the C# tutorial covered strings.
Do you like this Tutorial? Please link back to this article by copying one of the codes below.
URL: HTML link code: BB (forum) link code:
No comments: