In C language, the preprocessor directives are used to perform certain operations before the code is compiled. These directives begin with a hash symbol (#). Here are some common preprocessor directives:
- #include - This directive is used to include the contents of another file in the current file. Example: #include
2.#define - This directive is used to define a macro.
Example:
define PI 3.14159
- #ifdef, #ifndef, #else, #endif - These directives are used for conditional compilation. Example: #ifndef DEBUG printf("Debugging is off\n");
endif
- #pragma - This directive is used to provide additional instructions to the compiler. Example: #pragma pack(push, 1)
Here's an example of how preprocessor directives can be used in C code:
include
define PI 3.14159
int main() {
float radius = 5.0;
float area = PI * radius * radius;
printf("The area of the circle is: %f", area);
#ifdef DEBUG
printf("\nDebugging information:\n");
printf("The radius is: %f\n", radius);
printf("The area is: %f\n", area);
#endif
return 0;
}
In this example, we have used the #include directive to include the standard input-output header file. We have also defined a macro PI using the #define directive. Finally, we have used the #ifdef directive to conditionally compile some debugging statements.
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