Section 7: Simple Programming111
The HP-41C makes labeling programs easy. (Later, you will see how the calculator actually prompts you for the label characters.) While you are keying in an ALPHA label, the calculator ignores improper characters (e.g., , . : ) and does not accept any more than seven characters. The HP-41C does not accept any more than two digits in a numeric label.
Here are some examples of proper and improper program labels:
  Proper ALPHA   Proper Numeric
  TRIG01   00
  GO   83
  A (Used as a local label.)   06
  Improper ALPHA   Improper Numeric
  RUN. (Illegal period in name.)   1 (Too few digits.)
  COMPUTER. (Too many
  382 (Too many digits.)
Label Usage. Following are some considerations that you may find helpful in labeling your programs.
  • Numeric labels can be used any number of times, even in the same program.
  • If you label and execute a program with the same name used by the HP-41C for one of the HP-41C standard functions (e.g., DEG , ABS , etc.) the calculator will first search program memory for the program name. If it is found, the HP-41C will execute the named program. If the name is not found as a label in program memory, the HP-41C will then execute the standard HP-41C function having the same name.
The Complete Program
The complete program to solve for the area of a circle (one end of our cylindrical water heater) given its radius is now:
g LBL ALPHA CIRCLE ALPHA    Assigns the name (CIRCLE) to and defines beginning of the program.
g X2    Squares the radius.
g      Summons pi.
 ×     Multiplies r2 and π to give the area of the circle.
END    Defines end of program space in memory and stops the program (more about END later).