C#中的char、string和StringBuilder的使用详解

char someChar = 'a';//定义了一个字符
char newLine= '\n';//这是一个换行符

Console.WriteLine(char.ToUpper('c'));//输出的是一个大写的C
Console.WriteLine(char.ToLower('c'));//输出的是还是它自己
Console.WriteLine(char.ToUpper('C'));//输出的是还是它自己
Console.WriteLine(char.ToLower('C'));//输出的是一个小写的c
Console.WriteLine(char.IsWhiteSpace('c'));//输出为False
Console.WriteLine(char.IsWhiteSpace('\t'));//输出为True
Console.WriteLine(char.IsWhiteSpace(' '));//输出为True

Console.WriteLine(char.ToUpper('c'));//输出的是一个大写的C
Console.WriteLine(System.Char.ToUpper('c'));//输出的是一个大写的C

//使用固定区域性的大小写规则，不依赖于区域性的设置，以下这两种方式是等价的
Console.WriteLine(char.ToUpperInvariant('i'));//输出的是大写的I
Console.WriteLine(char.ToUpper('i', CultureInfo.InvariantCulture));

string s1 = "Hello";
string s2 = "First Line\r\nSecond Line";
string s3 = @\\server\fileshare\helloworld.cs;

Console.WriteLine(new string('*', 10));//输出的结果就是**********

char[] ca = "Hello".ToCharArray();
string s = new string(ca);

string empty = "";
Console.WriteLine(empty == ""); // True
Console.WriteLine(empty == string.Empty); // True
Console.WriteLine(empty.Length == 0); // True

string nullString = null;
Console.WriteLine(nullString == null); // True
Console.WriteLine(nullString == ""); // False
Console.WriteLine(nullString.Length == 0); // NullReferenceException

string str = "abcd";
char letter = str[1]; // letter = 'b'

// 分别依次输出字符1 、2 、3
foreach (var item in "123")
{
  Console.WriteLine(item);
}

Console.WriteLine("HelloWorld.cs".EndsWith(".cs")); // 返回结果为True
Console.WriteLine("HelloWorld.cs".Contains("World")); // 返回结果为True
Console.WriteLine("HelloWorld.cs".EndsWith(".CS")); // 返回结果为False
Console.WriteLine("HelloWorld.cs".Contains("world")); // 返回结果为False

Console.WriteLine("HelloWorld.cs".StartsWith("hello", StringComparison.InvariantCultureIgnoreCase)); // 返回结果为True

Console.WriteLine("abcde".IndexOf("cd")); // 结果为2
Console.WriteLine("abcde abcde".IndexOf("CD", 6, StringComparison.CurrentCultureIgnoreCase)); // 结果为8

Console.WriteLine("abc,de f".IndexOfAny(new char[] { ' ', ',' })); // 结果为3
Console.WriteLine("sdgp5jesu5fa9afe0".IndexOfAny("0123456789".ToCharArray())); // 结果为4

string left3 = "12345".Substring(0, 3); // 结果就是123
string mid3 = "12345".Substring(1, 3); // 结果为234
//如果忽略长度，那么就从起始位置一直到字符串的最后
string end3 = "12345".Substring(2); // 结果为345

string s1 = "helloworld".Insert(5, ","); // 结果为hello,world
string s2 = s1.Remove(5, 1); // 结果为helloworld

Console.WriteLine("12345".PadLeft(10, '*')); // 输出结果就是*****12345
Console.WriteLine("12345".PadLeft(10)); // 输出结果就是   12345

Console.WriteLine("  abc \r\n ".Trim().Length); // 结果为3

Console.WriteLine("hello world".Replace(" ", " | ")); // 结果为hello | world
Console.WriteLine("hello world".Replace(" ", "")); // 结果为helloworld

string[] words = "my name is bob".Split();
//打印结果依次输出my name is bob四个单词
foreach (var item in words)
{
  Console.WriteLine(item);
}
string[] split1 = "123-abc".Split('-');
//打印结果依次输出123和abc两个字符串
foreach (var item in split1)
{
  Console.WriteLine(item);
}
string[] split2 = "123-abc-".Split(new char[] { '-' }, StringSplitOptions.RemoveEmptyEntries);
//打印结果依次输出123和abc两个字符串，最后一个空项会被移除
foreach (var item in split2)
{
  Console.WriteLine(item);
}

string[] words = "my name is bob".Split();
Console.WriteLine(string.Join(",", words)); // 输出结果为一个字符串my,name,is,bob

string str1 = string.Concat("hello", "world"); // 结果为helloworld
string str2 = "hello" + "world"; // 结果为helloworld

string composite = "ab{0}cd{1}e";
Console.WriteLine(string.Format(composite, "123", 456)); // 结果为ab123cd456e

string composite = "Name={0, -20} Credit Limit={1,15:C}";
Console.WriteLine(string.Format(composite, "Bob", 500));
Console.WriteLine(string.Format(composite, "Elizatech", 20000));

int value = 32;
Console.WriteLine($"abc{value}"); //结果为abc32

public static bool Equals(String a, String b, StringComparison comparisonType);
public bool Equals(String value, StringComparison comparisonType);

Console.WriteLine("Hello" == "hello" ); // False
Console.WriteLine(string.Equals("Hello", "hello", StringComparison.OrdinalIgnoreCase)); // True

Console.WriteLine("u" == "ü"); // False
Console.WriteLine(string.Equals("u", "ü", StringComparison.CurrentCulture)); // ?

public int CompareTo(String strB);

Console.WriteLine("Base".CompareTo("Auto")); // 返回1
Console.WriteLine("Base".CompareTo("Base")); // 返回0
Console.WriteLine("Base".CompareTo("China")); // 返回-1
Console.WriteLine("base".CompareTo("Base")); // 返回-1
Console.WriteLine(string.Compare("base", "Base", true)); // 返回0

CultureInfo german = CultureInfo.GetCultureInfo("de-DE");
Console.WriteLine(string.Compare("Müller", "Muller", false, german)); // 返回结果是1

StringBuilder stringBuilder = new StringBuilder();
stringBuilder.Append("123");
stringBuilder.Append("456");
Console.WriteLine(stringBuilder.ToString()); // 结果为123456
stringBuilder.AppendLine("789");
Console.WriteLine(stringBuilder.ToString()); // 结果是123456789后面换行了
stringBuilder.AppendLine("abc");
Console.WriteLine(stringBuilder.ToString());