HP 50G, User Manual

Page: 671 / 887

Page 21-24
Fixing the program
The only possible explanation for the failure of the program to produce a
numerical result seems to be the lack of the command
NUM after the
algebraic expression ‘2*a^2+3’. Let’s edit the program by adding the missing
EVAL function. The program, after editing, should read as follows:
«
“
Enter a:
“
{
“
:a:
“
{2 0} V } INPUT
OBJ
→ →
a
«
‘
2*a^2+3
‘
NUM
» »
Store it again in variable FUNCa, and run the program again with a = 2. This
time, the result is 11, i.e., 2*2
2
+3 = 11.
Input string for two or three input values
In this section we will create a sub-directory, within the directory HOME, to hold
examples of input strings for one, two, and three input data values. These will
be generic input strings that can be incorporated in any future program, taking
care of changing the variable names according to the needs of each program.
Let’s get started by creating a sub-directory called PTRICKS (Programming
TRICKS) to hold programming tidbits that we can later borrow from to use in
more complex programming exercises. To create the sub-directory, first make
sure that you move to the HOME directory. Within the HOME directory, use the
following keystrokes to create the sub-directory PTRICKS:
³~~ptricks`
Enter directory name ‘PTRICKS’
„°
@)@MEM@@ @)@DIR@@ @CRDIR
Create directory
J
Recover variable listing
A program may have more than 3 input data values. When using input strings
we want to limit the number of input data values to 5 at a time for the simple
reason that, in general, we have visible only 7 stack levels. If we use stack level
7 to give a title to the input string, and leave stack level 6 empty to facilitate
reading the display, we have only stack levels 1 through 5 to define input
variables.