CODEWITHSUNDEEP
c#
user8214728
user8214728

Reputation:

What does hash sign # do in the C# especially in if-else Statements?

I came across the following code as shown below. But I couldn't understand how # can be worked in c#? 

 using System;
 public class Program
    {
        public static void Main(string[] args)
        {
        #if (!pi)
                    Console.WriteLine("i");
        #else 
                    Console.WriteLine("PI undefined");
        #endif
            Console.WriteLine("ok");
            Console.ReadLine();
        }
    }

Output: 

i
ok

Upvotes: 7

Views: 10107

Answers (2)

Reza Jenabi
Reza Jenabi

Reputation: 4319

C# compiler does not have a separate preprocessor. however, the directives are processed as if there was one. In C# the preprocessor directives are used to help in conditional compilation. Unlike C and C++ directives, they are not used to create macros. A preprocessor directive must be the only instruction on a line.

The #define preprocessor directive creates symbolic constants. #define lets you define a symbol such that, by using the symbol as the expression passed to the #if directive, the expression evaluates to true. Its syntax is as follows.

When the C# compiler encounters an #if directive, followed eventually by an #endif directive, it will compile the code between the directives only if the specified symbol is defined. the #if statement in C# is Boolean and only tests whether the symbol has been defined or no.

#define pi 

using System;

namespace Sample
{
    internal class Program
    {
        static void Main(string[] args)
        {
        #if (!pi)
            Console.WriteLine("i");
        #else
            Console.WriteLine("PI undefined");
        #endif
        Console.WriteLine("ok");
        Console.ReadLine();
        }
    }
}

Upvotes: 0

Alessio Cantarella
Alessio Cantarella

Reputation: 5211

In C# the lines starting with # are preprocessor directives (and they must be the only instruction on the line).

When the C# compiler encounters an #if directive, followed eventually by an #endif directive, it compiles the code between the directives only if the specified symbol is defined.

N.B. Unlike C and C++, you cannot assign a numeric value to a symbol. The #if statement in C# is Boolean and only tests whether the symbol has been defined or not.

Upvotes: 12

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