# SPECIAL - special considerations when using FRED.

If a space occurs between numbers in a line address, the numbers are added. For
example,

2 4,6 8 p

is equivalent to

6,14p

FRED uses the octal character `\777` for special internal purposes. Thus, the
character cannot be used in text.

If you are entering null lines as input for `\R` constructions, and text typed
in is separated by linefeeds rather than carriage returns, FRED ignores every other
linefeed.

FRED will give you an error if you attempt to read a file that contains a line
consisting of a single rub-out character. However, a line with two or more rub-outs is
acceptable.

### Extended Integers:

FRED uses numbers in many different ways: as line numbers, as repetition counts (in the
`U` command), for calculations with the `N` command, etc. All of these
numbers may be expressed as normal integers (decimal, base 10), or as *extended integers*.

An extended integer is written in the form

base#value

where `base` is a decimal number from 2 to 36 and `value` is a number
written in that base. For example,

8#100

has a base of 8 and a value of 100. It represents the octal (base 8) value 100 (decimal
64).

When a base is greater than 10, letters are used to represent digits that are greater
than 10. The most common example is hexadecimal (base 16) where the letters `A`
through `F` represent the "digits" 10 through 15.

255 16#FF 16#ff 8#377

all represent the same value. Notice that letters which represent digits can be used in
either upper or lower case -- the case is not relevant.

An extended integer may be used anywhere a normal integer can be (e.g. as a line number
or in a `U` or `N` command), with two exceptions:

- The base of an extended integer must be a decimal integer; it cannot be an extended
integer itself.
- An escape sequence of the form
`\nnn` always uses octal digits `nnn`;
extended integers are not allowed.

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