LI-COR LI-6400, Руководство пользователя

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Programming with LPL
Overview of LPL
22-4 Using the LI-6400
22
:FCT
Main
{
The function
Main
does the following: A prompt to enter 2 numbers is printed
on the display.
"Enter 2 values to average"
PRINT
The user's response is then parsed into two floating point values, which are
stored in variables
x
and
y
.
&y &x "%f %f" ENTER
x
and
y
are then summed, and the sum is divided by 2.
x y + 2 /
This result is printed, and the program pauses until the user presses a key, at
which time the program terminates.
y x "\nThe average of %f and %f is %f\n"
PRINT
"\n\nPress Any Key"
PRINT
GETKEY DROP
The View From the Stack
LPL is a post-fix language, whose operation centers about an abstraction
known as a stack. The stack is a ÒLast In - First OutÓ list of objects. The key
to understanding an LPL program is to consider each item (keyword, string,
number, etc.) in the program, and keep track of what it does to the stack. WeÕll
go through the program in Figure 22-1 again, this time with special emphasis
on the stack.
We illustrate stack operations by picturing the stack as a horizontal collection
of boxes, with the top of the stack being the right-most box. We start with an
empty stack. First, the prompting stringÕs address is pushed onto the stack,
and the
PRINT pops it back off.
Operation
The Stack
3 2 1
1. Stack is empty:
2. "Enter 2 ..." Address of "Enter 2..."
3.
PRINT