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C# Coding Conventions (C# Programming Guide)

The C# Language Specification does not define a coding standard. However, the guidelines in this topic are used by Microsoft to develop samples and documentation.

Coding conventions serve the following purposes:

  • They create a consistent look to the code, so that readers can focus on content, not layout.

  • They enable readers to understand the code more quickly by making assumptions based on previous experience.

  • They facilitate copying, changing, and maintaining the code.

  • They demonstrate C# best practices.

  • In short examples that do not include using directives, use namespace qualifications. If you know that a namespace is imported by default in a project, you do not have to fully qualify the names from that namespace. Qualified names can be broken after a dot (.) if they are too long for a single line, as shown in the following example.

    var currentPerformanceCounterCategory = new System.Diagnostics.
        PerformanceCounterCategory();
    
  • You do not have to change the names of objects that were created by using the Visual Studio designer tools to make them fit other guidelines.

Good layout uses formatting to emphasize the structure of your code and to make the code easier to read. Microsoft examples and samples conform to the following conventions:

  • Use the default Code Editor settings (smart indenting, four-character indents, tabs saved as spaces). For more information, see Options,Text Editor, C#, Formatting.

  • Write only one statement per line.

  • Write only one declaration per line.

  • If continuation lines are not indented automatically, indent them one tab stop (four spaces).

  • Add at least one blank line between method definitions and property definitions.

  • Use parentheses to make clauses in an expression apparent, as shown in the following code.

    if ((val1 > val2) && (val1 > val3))
    {
        // Take appropriate action.
    }
    

  • Place the comment on a separate line, not at the end of a line of code.

  • Begin comment text with an uppercase letter.

  • End comment text with a period.

  • Insert one space between the comment delimiter (//) and the comment text, as shown in the following example.

    // The following declaration creates a query. It does not run 
    // the query.
    
  • Do not create formatted blocks of asterisks around comments.

The following sections describe practices that the C# team follows to prepare code examples and samples.

  • Use the + operator to concatenate short strings, as shown in the following code.

    string displayName = nameList[n].LastName + ", " + nameList[n].FirstName;
    
  • To append strings in loops, especially when you are working with large amounts of text, use a StringBuilder object.

    var phrase = "lalalalalalalalalalalalalalalalalalalalalalalalalalalalalala";
    var manyPhrases = new StringBuilder();
    for (var i = 0; i < 10000; i++)
    {
        manyPhrases.Append(phrase);
    }
    //Console.WriteLine("tra" + manyPhrases);
    

  • Use implicit typing for local variables when the type of the variable is obvious from the right side of the assignment, or when the precise type is not important.

    // When the type of a variable is clear from the context, use var  
    // in the declaration. 
    var var1 = "This is clearly a string.";
    var var2 = 27;
    var var3 = Convert.ToInt32(Console.ReadLine());
    
  • Do not use var when the type is not apparent from the right side of the assignment.

    // When the type of a variable is not clear from the context, use an 
    // explicit type. 
    int var4 = ExampleClass.ResultSoFar();
    
  • Do not rely on the variable name to specify the type of the variable. It might not be correct.

    // Naming the following variable inputInt is misleading.  
    // It is a string. 
    var inputInt = Console.ReadLine();
    Console.WriteLine(inputInt);
    
  • Avoid the use of var in place of dynamic.

  • Use implicit typing to determine the type of the loop variable in for and foreach loops.

    The following example uses implicit typing in a for statement.

    var syllable = "ha";
    var laugh = "";
    for (var i = 0; i < 10; i++)
    {
        laugh += syllable;
        Console.WriteLine(laugh);
    }
    

    The following example uses implicit typing in a foreach statement.

    foreach (var ch in laugh)
    {
        if (ch == 'h')
            Console.Write("H");
        else
            Console.Write(ch);
    }
    Console.WriteLine();
    

  • In general, use int rather than unsigned types. The use of int is common throughout C#, and it is easier to interact with other libraries when you use int.

  • Use the concise syntax when you initialize arrays on the declaration line.

    // Preferred syntax. Note that you cannot use var here instead of string[]. 
    string[] vowels1 = { "a", "e", "i", "o", "u" };
    
    
    // If you use explicit instantiation, you can use var. 
    var vowels2 = new string[] { "a", "e", "i", "o", "u" };
    
    // If you specify an array size, you must initialize the elements one at a time. 
    var vowels3 = new string[5];
    vowels3[0] = "a";
    vowels3[1] = "e";
    // And so on.
    

  • Use the concise syntax to create instances of a delegate type.

    // First, in class Program, define the delegate type and a method that   
    // has a matching signature. 
    
    // Define the type. 
    public delegate void Del(string message);
    
    // Define a method that has a matching signature. 
    public static void DelMethod(string str)
    {
        Console.WriteLine("DelMethod argument: {0}", str);
    }
    
    // In the Main method, create an instance of Del. 
    
    // Preferred: Create an instance of Del by using condensed syntax.
    Del exampleDel2 = DelMethod;
    
    // The following declaration uses the full syntax.
    Del exampleDel1 = new Del(DelMethod);
    

  • Use a try-catch statement for most exception handling.

    static string GetValueFromArray(string[] array, int index)
    {
        try
        {
            return array[index];
        }
        catch (System.IndexOutOfRangeException ex)
        {
            Console.WriteLine("Index is out of range: {0}", index);
            throw;
        }
    }
    
  • Simplify your code by using the C# using statement. If you have a try-finally statement in which the only code in the finally block is a call to the Dispose method, use a using statement instead.

    // This try-finally statement only calls Dispose in the finally block.
    Font font1 = new Font("Arial", 10.0f);
    try
    {
        byte charset = font1.GdiCharSet;
    }
    finally
    {
        if (font1 != null)
        {
            ((IDisposable)font1).Dispose();
        }
    }
    
    
    // You can do the same thing with a using statement. 
    using (Font font2 = new Font("Arial", 10.0f))
    {
        byte charset = font2.GdiCharSet;
    }
    

  • To avoid exceptions and increase performance by skipping unnecessary comparisons, use && instead of & and || instead of | when you perform comparisons, as shown in the following example.

    Console.Write("Enter a dividend: ");
    var dividend = Convert.ToInt32(Console.ReadLine());
    
    Console.Write("Enter a divisor: ");
    var divisor = Convert.ToInt32(Console.ReadLine());
    
    // If the divisor is 0, the second clause in the following condition 
    // causes a run-time error. The && operator short circuits when the 
    // first expression is false. That is, it does not evaluate the 
    // second expression. The & operator evaluates both, and causes  
    // a run-time error when divisor is 0. 
    if ((divisor != 0) && (dividend / divisor > 0))
    {
        Console.WriteLine("Quotient: {0}", dividend / divisor);
    }
    else
    {
        Console.WriteLine("Attempted division by 0 ends up here.");
    }
    

  • Use the concise form of object instantiation, with implicit typing, as shown in the following declaration.

    var instance1 = new ExampleClass();
    

    The previous line is equivalent to the following declaration.

    ExampleClass instance2 = new ExampleClass();
    
  • Use object initializers to simplify object creation.

    // Object initializer. 
    var instance3 = new ExampleClass { Name = "Desktop", ID = 37414, 
        Location = "Redmond", Age = 2.3 };
    
    // Default constructor and assignment statements. 
    var instance4 = new ExampleClass();
    instance4.Name = "Desktop";
    instance4.ID = 37414;
    instance4.Location = "Redmond";
    instance4.Age = 2.3;
    

  • If you are defining an event handler that you do not need to remove later, use a lambda expression.

    public Form2()
    {
        // You can use a lambda expression to define an event handler. 
        this.Click += (s, e) =>
            {
                MessageBox.Show(
                    ((MouseEventArgs)e).Location.ToString());
            };
    }
    
    // Using a lambda expression shortens the following traditional definition. 
    public Form1()
    {
        this.Click += new EventHandler(Form1_Click);
    }
    
    void Form1_Click(object sender, EventArgs e)
    {
        MessageBox.Show(((MouseEventArgs)e).Location.ToString());
    }
    

  • Call static members by using the class name: ClassName.StaticMember. Do not access a static member that is defined in a base class from a derived class.

  • Use meaningful names for query variables. The following example uses seattleCustomers for customers who are located in Seattle.

    var seattleCustomers = from cust in customers
                           where cust.City == "Seattle" 
                           select cust.Name;
    
  • Use aliases to make sure that property names of anonymous types are correctly capitalized, using Pascal casing.

    var localDistributors =
        from customer in customers
        join distributor in distributors on customer.City equals distributor.City
        select new { Customer = customer, Distributor = distributor };
    
  • Rename properties when the property names in the result would be ambiguous. For example, if your query returns a customer name and a distributor ID, instead of leaving them as Name and ID in the result, rename them to clarify that Name is the name of a customer, and ID is the ID of a distributor.

    var localDistributors2 =
        from cust in customers
        join dist in distributors on cust.City equals dist.City
        select new { CustomerName = cust.Name, DistributorID = dist.ID };
    
  • Use implicit typing in the declaration of query variables and range variables.

    var seattleCustomers = from cust in customers
                           where cust.City == "Seattle" 
                           select cust.Name;
    
  • Align query clauses under the from clause, as shown in the previous examples.

  • Use where clauses before other query clauses to ensure that later query clauses operate on the reduced, filtered set of data.

    var seattleCustomers2 = from cust in customers
                            where cust.City == "Seattle" 
                            orderby cust.Name
                            select cust;
    
  • Use multiple from clauses instead of a join clause to access inner collections. For example, a collection of Student objects might each contain a collection of test scores. When the following query is executed, it returns each score that is over 90, along with the last name of the student who received the score.

    // Use a compound from to access the inner sequence within each element. 
    var scoreQuery = from student in students
                     from score in student.Scores
                     where score > 90
                     select new { Last = student.LastName, score };
    

Follow the guidelines in Secure Coding Guidelines.

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