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C - Why int main() Returns 0

In C programming, the int main() function returns an integer value, typically 0, as a convention to indicate the exit status of the program to the operating system. The return value of 0 from the main function is considered to indicate a successful and error-free execution of the program. Here's why it is a common practice:

  1. Exit Status: When a C program terminates, it can return an integer value to the operating system. This exit status is used to indicate whether the program completed successfully or encountered an error during execution.
  2. Success Indicator: By convention, a return value of 0 from the main function signifies that the program executed without errors or issues. This is often referred to as a "successful" or "normal" exit.
  3. Error Codes: Other integer values (typically non-zero) can be used to indicate specific error conditions or abnormal terminations. These error codes can help identify the nature of the problem that caused the program to exit.

For example, a program might use a non-zero exit code to indicate that it encountered an error while processing a file or that it couldn't open a required resource.


#include <stdio.h>

int main() {
    // Some program logic here...
    
    if (/* An error condition */) {
        // Return a non-zero value to indicate an error
        return 1;
    }

    // Program executed successfully
    return 0;
}

In the above example, the program checks for an error condition and returns 1 if an error is encountered, indicating an abnormal exit. Otherwise, it returns 0 to indicate successful execution.

The return value of 0 is not mandatory, but it has become a convention in C programming and many other programming languages to help identify whether a program executed successfully or encountered an issue when it is run from the command line or by other programs/scripts.

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