Which of the following standard input value is used for the default keyboard?
In computing, standard input (stdin) is a stream from which a program reads its input data. The default standard input device is the keyboard. Standard input is usually represented by file descriptor 0 (zero).
When you're writing a program, you don't typically need to specify the keyboard explicitly as the input source. Instead, your program will read from stdin, and it is understood that this will be the keyboard unless the input is redirected (for example, from a file or another command in a pipeline).
For example, in most POSIX-compatible operating systems (like Linux and macOS), when you run a program from the command line without any redirection, the program receives input you type from the keyboard. If you redirect the input using the `<` operator, you can change the source of standard input to be a file instead of the keyboard:
```sh
myprogram < inputfile.txt
```
This tells the shell to use the contents of `inputfile.txt` as the standard input for `myprogram` instead of the keyboard.
In programming languages such as C, the standard input stream is accessed using the `stdin` file pointer provided by the standard I/O library, while in Python, you might use functions like `input()` to read from standard input, which is by default the keyboard, unless redirected.