Preprocessor Directives

Definition:
These are commands that are processed before actual compilation. They begin with #.

Common Directives:

Directive

Description

#include

Includes standard/library files

#define

Defines macros/constants

#ifdef / #ifndef

Conditional compilation

#undef

Undefines a macro

#pragma

Special compiler instructions

 

Example

#include <stdio.h>

#define PI 3.14

int main() {

    printf(“Value of PI: %f\n”, PI);

    return 0;

}

 

Tips & Best Practices

  • Always initialize variables.
  • Use meaningful variable and function names.
  • Avoid using too many goto statements.
  • Comment your code for clarity.
  • Prefer functions to break down complex code.
  • Always free() dynamically allocated memory.
  • Validate user input wherever necessary.
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