Thursday, October 24, 2013

HP Prime Programming Tutorial #1: LOCAL, RETURN

Over the next month, maybe month and a half, I plan to post programming tutorials for the HP (Hewlett Packard) Prime.

If you have programmed with the HP 38G, 39g, or 39gii, this language will be similar to those. The programming language for the Prime is named the HP Prime Programming Language (HPPP).

Throughout this tutorial, I am going to use the latest version of the software.

How to start writing a program:

1. Press Shift + 1 (Program).
2. Press New. It is the second touch key.
3. Enter the name of the program. Pressing the ALPHA key twice will turn on UPPERCASE ΑLPHA-LOCK. Pressing ALPHA, Shift, ALPHA will turn on lowercase alpha-lock. To exit any lock, press the ALPHA key one more time. When happy with the name, press Enter.




Rules for Program Names:

1. Letters, numbers, and the underscore character (_) only.

2. The program name must start with a letter.


Structure of a HP Prime Program

A HPPP program is encased of an EXPORT - BEGIN - END structure. The layout is generally like this:

EXPORT program_name(arguments)
BEGIN
commands and comments go here
END;


Each line containing a command generally must end with a semicolon (;). A semicolon can by type by pressing ALPHA then the Plus key ( + ).

Comments can be typed. The are designated by two forward slashes. The slashes are typed by pressing the Divide key ( ÷ ). Anything in the line following the two slashes is ignored in running the program.


SQIN

Our first program is SQIN, because "Hello World" programs are so 2000s. SQIN takes a number, squares it, then calculates the reciprocal. In short we are defining a custom function:

SQIN(x) = 1/x^2

Commands:

RETURN: returns a result to the stack (home page). You can return numbers, lists, vectors, matrices, strings, or a combination of these times.
Access: Tmplt, 1. Block, 2. RETURN

All the program code in this tutorial series will be shown in Courier font.

EXPORT SQIN(X)
BEGIN
RETURN 1/X^2;
END;



Tip: You can check the syntax of the program just by pressing the Check soft key in the program editor. HP Prime will inform you if there is a syntax error and attempt to point you to the error. If there are no syntax errors, the Prime states "No errors in the program". I use the Check command all the time.


How to run the programs:

Home Mode - Textbook Entry,
Home Mode - Algebraic Entry,
CAS Mode:


Type the program name. Follow the name with parenthesis and enclose the required arguments.

Or use the Toolbox (top row of white keys, 2nd key from the left, it looks like a tool box), select the User touch key, select the program, and input the required arguments.

Home Mode - RPN Entry:

Enter each argument, separate each entry by pressing the Enter key. Type the name, and in the parenthesis state the number of arguments.

For example, if the program TEST has four arguments, the RPN stack would like this:

4: argument_1
3: argument_2
2: argument_3
1: argument_4
TEST(4) to run the program.


Examples to try with SQIN:

SQIN(5) returns .04
SQIN(36) returns .000771604938


The next program will demonstrate the concept of local variables.


MOPMT

LOCAL: Declares any variables to be local to the program. In other words, the variables are created, used, possibly displayed during program execution, and deleted at program termination.
Access: Tmplt, 4. Variable, 1. LOCAL


Tip: You can declare local variables and assign an initial value at the same time. For example: LOCAL K:=1; stores 1 in K and makes K a local variable.


MOPMT calculates the monthly payment of a loan. The arguments are: the loan amount (L), the interest rate (R), and the number of months (M).

EXPORT MOPMT(L,R,M)
BEGIN
LOCAL K:=R/1200;
K:=L*K/(1-(1+K)^-M);
RETURN "Payment ="+K;
END;



Tip: Use RETURN, TEXTOUT_P, and PRINT to return custom strings, which combine results, messages, and calculations. Parts are connected with a plus sign.


Examples:
MOPMT(4000, 9.5, 30) returns 150.317437565
MOPMT(370000, 3.5, 360) returns 1661.46534383

Try this and next time in the series I will highlight other things we can do with HPPP. Thanks!

Eddie

This blog is property of Edward Shore. 2013 









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