What does the standard function return by default in a program or system?

The default standard function in most programs or systems returns an exit code, which is usually 0 upon successful completion. This code signals to the operating system or calling process that the program has finished without errors. If an error occurs, a non-zero value is returned, which may indicate the type of error.

For example, in Unix-like systems:

• 0 — successful execution
• 1 and above — various errors

This allows automation of processing program execution results.