C programming

Pre-processor directives

In C programming, preprocessor directives are special lines beginning with # that are processed by the preprocessor before actual compilation. These directives provide instructions to the preprocessor to perform various tasks like including header files, defining constants, and conditional compilation. Here are the main types of preprocessor directives.

Include Directive (#include):Includes the contents of a file into the source code at the point where the directive appears.

Define Directive (#define): Defines a macro, which is a name representing a sequence of characters, which can be a value, an expression, or a statement.

Undef Directive (#undef): Undefines a previously defined macro.

Conditional Directive (#if, #ifdef, #ifndef, #else, #elif, #endif): These directives are used for conditional compilation based on certain conditions.

Error Directive (#error): Causes the preprocessor to generate an error message during compilation.

Pragma Directive (#pragma):Provides additional instructions to the compiler, typically used for optimization or platform-specific directives.

Program:

                            // Including standard input/output library
#include <stdio.h>

// Defining a macro using #define
#define PI 3.14159

// Conditional compilation using #ifdef and #ifndef
#ifndef GREETING
#define GREETING "Hello, World!"
#endif

// Function prototype
void printMessage();

// Main function
int main() {
    // Using #ifdef to check if a macro is defined
    #ifdef DEBUG
    printf("Debug mode is enabled.\n");
    #else
    printf("Debug mode is not enabled.\n");
    #endif

    // Using #if and #else to check conditions
    #if defined(PI)
    printf("Value of PI: %f\n", PI);
    #else
    printf("PI is not defined.\n");
    #endif

    // Using #undef to undefine a macro
    #undef PI

    // Using #ifndef to check if a macro is not defined
    #ifndef PI
    printf("PI is not defined after #undef.\n");
    #endif

    // Using #ifdef to check if a macro is defined
    #ifdef GREETING
    printf("%s\n", GREETING);
    #endif

    // Calling a function with preprocessor directives
    printMessage();

    return 0;
}

// Function definition
void printMessage() {
    // Using #warning to generate a compiler warning
    #warning This is a warning message!

    // Using #error to generate a compiler error
    #error This is an error message!
}

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With supporting text below as a natural lead-in to additional content.

Q1. A variable name can have ?

A. Any special symbol

B. Blank space

C. Comma ( , )

D. Underscore

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B. { }

C. [ ]

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Getting Started With C

Pre-processor directives

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