#else in C

 The #else directive in C is used alongside #if and #elif to provide an alternative code path when the preceding conditions are not met.

 It acts as a catch-all for conditions that were not satisfied by the preceding #if or #elif directives.

 This directive enhances code versatility by allowing you to specify what should happen if none of the earlier conditions are true.

Syntax of #else in C

#if expression
    // code to be compiled if expression is true (non-zero)
#elif expression2
    // code to be compiled if expression2 is true (non-zero)
#else
    // code to be compiled if none of the above conditions are met
#endif

Example:

 // Program for #else in C
#include<stdio.h>

#define DEBUG_MODE 0

int main() {
    
#if DEBUG_MODE
    printf("Debugging is enabled.\n");
#elif RELEASE_MODE
    printf("Running in release mode.\n");
#else
    printf("No mode selected.\n");
#endif

    return 0;
}

Output:

No mode selected.

In this example:

 The DEBUG_MODE macro is defined with a value of 0.

 There's no RELEASE_MODE macro defined.

 The #if DEBUG_MODE directive checks if DEBUG_MODE is true (non-zero), but it's not, so it skips to the #else part.

 The message "No mode selected." is printed because neither DEBUG_MODE nor RELEASE_MODE is true.

Uses of #else in C

 Default Behavior: To specify a default behavior or code path when no specific conditions are met.

#if DEBUG
    // Debugging code
#else
    // Default behavior
#endif

 Fallback Options: To provide alternative code paths or configurations when certain conditions are not satisfied.

#ifdef FEATURE_A
    // Code related to Feature A
#else
    // Fallback code or alternative feature
#endif

 Configuration Management: To manage different configurations or build options and specify default settings when specific conditions are not defined.

#if defined(_WIN32)
    // Windows-specific code
#elif defined(__linux__)
    // Linux-specific code
#else
    // Default code
#endif

 The #else directive plays a crucial role in handling cases where none of the preceding conditions are true, allowing for graceful fallbacks or default behaviors in C programs.