5.3 Stack Basics
Calc uses RPN notation. If you are not familar with RPN, Note: RPN
To add the numbers 1 and 2 in Calc you would type the keys: `1 <RET>
2 +'. (<RET> corresponds to the <ENTER> key on most calculators.) The
first three keystrokes "push" the numbers 1 and 2 onto the stack. The
`+' key always "pops" the top two numbers from the stack, adds them,
and pushes the result (3) back onto the stack. This number is ready for
further calculations: `5 -' pushes 5 onto the stack, then pops the 3
and 5, subtracts them, and pushes the result (-2).
Note that the "top" of the stack actually appears at the _bottom_ of
the buffer. A line containing a single `.' character signifies the end
of the buffer; Calculator commands operate on the number(s) directly
above this line. The `d t' (`calc-truncate-stack') command allows you
to move the `.' marker up and down in the stack; Note: Truncating the
Stack elements are numbered consecutively, with number 1 being the
top of the stack. These line numbers are ordinarily displayed on the
lefthand side of the window. The `d l' (`calc-line-numbering') command
controls whether these numbers appear. (Line numbers may be turned off
since they slow the Calculator down a bit and also clutter the display.)
The unshifted letter `o' (`calc-realign') command repositions the
cursor to its top-of-stack "home" position. It also undoes any
horizontal scrolling in the window. If you give it a numeric prefix
argument, it instead moves the cursor to the specified stack element.
The <RET> (or equivalent <SPC>) key is only required to separate two
consecutive numbers. (After all, if you typed `1 2' by themselves the
Calculator would enter the number 12.) If you press `RET' or `SPC'
_not_ right after typing a number, the key duplicates the number on the
top of the stack. `<RET> *' is thus a handy way to square a number.
The <DEL> key pops and throws away the top number on the stack. The
<TAB> key swaps the top two objects on the stack. Note: Stack and
Trail, for descriptions of these and other stack-related commands.
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