c# string-basics

formatting

设置货币格式

:C 货币格式说明符用于将变量以货币形式显示

 Console.WriteLine($"Price：{price:C}")
 decimal price = 123.45m;
 int discount = 50;
 Console.WriteLine($"Price: {price:C} (Save {discount:C})");

 // Output：
 // Price: $123.45 (Save $50.00)

请注意，无论使用 int 还是 decimal，在大括号内的标记中添加 :C 都会将数字格式化为货币。

设置数值格式

N 数值格式说明符使数字更具可读性。

decimal measurement = 123456.78912m;
Console.WriteLine($"Measurement: {measurement:N} units");

// output:
// Measurement: 123,456.79 units

N 数值格式说明符默认仅显示小数点后两位数字。如果要以更高的精度显示，可通过在说明符后面添加数字来实现。

decimal measurement = 123456.78912m;
Console.WriteLine($"Measurement: {measurement:N4} units");

// output:
// Measurement: 123,456.7891 units

设置百分比的格式

使用 P 格式说明符设置百分比的格式。

decimal tax = .36785m;
Console.WriteLine($"Tax rate: {tax:P2}");

// output:
// Tax rate: 36.79 %

添加空白进行格式设置的方法（PadLeft()、PadRight()）
比较两个字符串或辅助比较的方法（Trim()、TrimStart()、TrimEnd()、GetHashcode()、Length 属性）
帮助确定字符串内部内容，甚至只检索部分字符串的方法（Contains()、StartsWith()、EndsWith()Substring()）
通过替换、插入或删除部件来更改字符串内容的方法（Replace()、Insert()、Remove()）
将字符串转换为字符串或字符数组的方法（Split()、ToCharArray()）

modify-content

避免 magic 值

避免硬编码的 magic 值。改为定义 const 变量。初始化后，常数变量的值无法更改。

string message = "What is the value <span>between the tags</span>?";

int openingPosition = message.IndexOf("<span>");
int closingPosition = message.IndexOf("</span>");

openingPosition += 6;
int length = closingPosition - openingPosition;
Console.WriteLine(message.Substring(openingPosition, length));

在前面的代码中，像 "<span>" 这样的硬编码字符串称作“magic 字符串”，而像 6 这样的硬编码数值称作“幻数”。由于多种原因，你并不需要这些“magic”值，因此应尽量避免使用它们。

如果你在代码中多次对字符串 "<span>" 进行了硬编码，但将其中一个实例误拼为 "<sapn>"。或者将字符串 "<span>" 更改为 "<div>"，但忘记更改数字 6，则代码将产生非预期结果。

string message = "What is the value <span>between the tags</span>?";

const string openSpan = "<span>";
const string closeSpan = "</span>";

int openingPosition = message.IndexOf(openSpan);
int closingPosition = message.IndexOf(closeSpan);

openingPosition += openSpan.Length;
int length = closingPosition - openingPosition;
Console.WriteLine(message.Substring(openingPosition, length));

IndexOfAny 和 LastIndexOf
- LastIndexOf() 返回字符或字符串在另一个字符串中最后出现的位置。
- IndexOfAny() 返回在另一个字符串内首次出现 char 数组的位置。

    string message = "(What if) I have [different symbols] but every {open symbol} needs a [matching closing symbol]?";

    // The IndexOfAny() helper method requires a char array of characters. 
    // You want to look for:

    char[] openSymbols = { '[', '{', '(' };

    // You'll use a slightly different technique for iterating through 
    // the characters in the string. This time, use the closing 
    // position of the previous iteration as the starting index for the 
    //next open symbol. So, you need to initialize the closingPosition 
    // variable to zero:

    int closingPosition = 0;

    while (true)
    {
        int openingPosition = message.IndexOfAny(openSymbols, closingPosition);

        if (openingPosition == -1) break;

        string currentSymbol = message.Substring(openingPosition, 1);

        // Now  find the matching closing symbol
        char matchingSymbol = ' ';

        switch (currentSymbol)
        {
            case "[":
                matchingSymbol = ']';
                break;
            case "{":
                matchingSymbol = '}';
                break;
            case "(":
                matchingSymbol = ')';
                break;
        }

        // To find the closingPosition, use an overload of the IndexOf method to specify 
        // that the search for the matchingSymbol should start at the openingPosition in the string. 

        openingPosition += 1;
        closingPosition = message.IndexOf(matchingSymbol, openingPosition);

        // Finally, use the techniques you've already learned to display the sub-string:

        int length = closingPosition - openingPosition;
        Console.WriteLine(message.Substring(openingPosition, length));
    }

    // 输出：
    What if
    different symbols
    open symbol
    matching closing symbol

Edward Chu's blog

Edward Chu's blog

c# string-basics

formatting

设置数值格式

设置百分比的格式

modify-content

避免 magic 值