Thread: How to use conditional?

I have seen in many link there is more theoretical description about preprocessor

C Preprocessor and Macros


I want to experiment by writing some code

Code:

#include <stdio.h>#include "other.h"
 
int main(void)
{


    return 0;
}

Code:

    #ifdef x      printf("hello\n");      
   #endif

Originally Posted by Zeus_

> I want to experiment by writing some code

Good luck!

I do not understand what should be in main function that's why left main empty. I don't found complete code that's why tried with my own code

Originally Posted by abhi143

I do not understand what should be in main function that's why left main empty. I don't found complete code that's why tried with my own code

Header files should contain extern function and extern Global data declarations, #defines, other preprocessor directives, etc..., but not executable code such as the printf statement.

I would write the code you provided as:

Code:

#include <stdio.h>

#define X 1

int main(void)
{

 #ifdef X
   printf("hello\n");
 #endif

   return 0;
}

#define macros are by tradition, all UPPERCASE.

"#define X 1" could be put in a header file, but with code this simple, why bother.

Not the best example of the use of #ifdef, etc...

Originally Posted by rstanley

#define macros are by tradition, all UPPERCASE.

"#define X 1" could be put in a header file, but with code this simple, why bother.

Not the best example of the use of #ifdef, etc...

As much as I have seen, we keep the micro in the header file. So I created two files main.c other.h

What could be best example for #ifdef, #if, #defined, #else and #elseif directives ?

Three examples I can see used are, stubbing out code temporarily, header file choice, and inclusion of debug code during development:

Code:

#ifdef DEBUG
    // Code with debug statements
#else
    // Production code without any debug statements
#endif

Code:

#ifdef  _WIN32
    // Windows version of a header file
#else
    // Linux header file inclusion
#endif

Code:

#if 0
    ...
    /*
        The best way to stub out a multiple line comment
    */
    ...
#endif

There are other uses of these and other Preprocessor directives.

Rather than point you to an online tutorial, you should study a good book on the C Programming Language that will explain all preprocessor directives, and many other features you need to learn and use.