why do some lines not have semicolon in C#?

Question

I am just trying to figure out the technical reason why in the below some lines do not end with a semicolon but other lines do - what is it about a semicolon that C# expects in some lines then others....

In fact whilst writing this I noticed that the statements that have to have curly brackets {} do not need semicolons but the lines that are on its own "Console.WriteLine" do need it.

Really trying to find the technical reasons for this...

ie:

namespace checkPackage     **//no semicolon**
{
    class Program      **//no semicolon**
    {
        static void Main(string[] args)     **//no semicolon**
        {
            listFilesInDirectory(@"C:\Temp\");    **//NEEDS a semicolon**
        }

        static void listFilesInDirectory(string workingDirectory)   **//no semicolon**
        {
            string[] filePaths = Directory.GetFiles(workingDirectory);  **//NEEDS a semicolon**

            foreach (string filePath in filePaths)   **//no semicolon**
            {
                Console.WriteLine(filePath);  **//NEEDS a semicolon**
            }

        }
    }
}

Answer 1

The semi-colon isn't a line terminator... it's a statement terminator. There's a semi-colon at the end of every expression statement and declaration statement.

(if, for etc statements aren't expression or declaration statements.)

So for example:

public class Foo // Part of a class declaration
{
    int x = 0; // Declaration statement

    public void Bar() // Part of a method declaration
    {
        Console.WriteLine(x); // Expression statement (using an invocation expression)
    } // End of the method declaration, but not a declaration statement 

} // End of class declaration, but not a declaration statement

The purpose of requiring them is so that the compiler can tell when you wanted to end the statement instead of continuing on the next line:

 int x = 5;
 int y = x // This isn't the end of the statement!
         + 5; // This is...

One alternative (used by VB, for example) is to have a line continuation where you want to explicitly continue onto the next line even though the current line would be a valid statement.

As noted in comments, the do statement is an anomaly here. I see no obvious reason why this shouldn't be valid:

do { } while (false)

... but it isn't. It may be related to the fact that the plain while statement needs a statement body, e.g. while (true); (empty statement) or while (true) {} (block statement). The closest I can come is "because the C# specification says the do statement needs a semi-colon at the end..."

Answer 2

The reason? Because the spec says so:

A statement can consist of a single line of code that ends in a semicolon, or a series of single-line statements in a block. A statement block is enclosed in {} brackets and can contain nested blocks.

The foreach definition is followed by a statement, which must either be enclosed in {} or end on a semicolon. This statement is then referred to as the loops body.

This might not be an adequate answer to the question "why". To go deeper into this, you'd really need to ask the designers. I suppose, they wanted to make it close to C-Syntax, as opposed to other languages where the line-break serves a similar purpose. (Python iirc)

If you want a more formal definition, download the C# Language Specification and read section 1.2 to 1.5.

Answer 3

There are two kinds of statements, simple statements and compound statements. The loops and method declarations are compound statements. Each simple statement end with semicolon but compound statements don't end with semicolon. From msdn

A compound statement consists of zero or more statements enclosed in curly braces ({ }). A compound statement can be used anywhere a statement is expected. Compound statements are commonly called "blocks."

The curly braces specifies the begin and the end of a compound statement.So compiler looks for the braces instead of the semicolon to determine the beginning and the end of the statement.