return 0
In the C and C++ programming languages,return 0; is a statement employed within the main function to return an integer value of zero as the program's exit status to the operating system, signifying successful execution without errors.[1][2] This practice adheres to a longstanding convention in Unix-like operating systems, where an exit status of 0 universally denotes success, while non-zero values indicate failures, exceptions, or specific error conditions that can be checked by parent processes or scripts.[3][4] The construct equates to EXIT_SUCCESS, a macro defined in standard headers like <stdlib.h>, ensuring portability across environments despite the absence of a strict mandate in the core C language specification for main's return type in all cases.[2]
Since the C99 standard, omitting an explicit return statement in main implicitly behaves as return 0;, allowing programs to terminate cleanly without the line, though explicit usage remains recommended for clarity and compatibility with pre-C99 compilers or non-standard environments.[5] This mechanism enables error handling in pipelines, conditional execution in shells (e.g., via $? checking the status), and integration with build systems or automation tools that rely on exit codes for workflow control, underscoring its foundational role in systems programming and software reliability.[6][3]