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:

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


    return 0;
}

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Code:

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

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> I want to experiment by writing some code

Good luck!

Quote:

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Originally Posted by Zeus_

> I want to experiment by writing some code

Good luck!

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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

Quote:

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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

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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:

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#include <stdio.h>

#define X 1

int main(void)
{

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

  return 0;
}

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#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...

Quote:

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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...

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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:

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

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Code:

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

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Code:

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

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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.