HP 15c - Manual (Page 104)

104 Section 9: Subroutines
Example: Nesting. The following subroutine, labeled ―.4‖, calculates the
value of the expression 2 2 2 2
t z y x
  
as part of a larger calculation in a
larger program. The subroutine calls upon another subroutine (a nested
subroutine), labeled ―.5‖, to do the repetitive squaring.
The program is executed after placing the variables t, z, y, and x into the T-,
Z-, Y-, and X-registers.
Keystrokes
´ b.4
Start of main
subroutine.
| x
x
2
.
G.5
Calculates y
2
and
x
2
+ y
2
.
G.5 
Calculates z
2
and
X
2
+ y
2
+ z
2
.
G.5 
Calculates t
2
and
x
2
+ y
2
+ z
2
+ t
2
.
¤ 
2 2 2 2
t z y x
  
| n
End of main subroutine;
returns to main program.
´ b.5
Start of nested
subroutine.
®
| x
Calculates a square and
+
adds it to current sum of squares.
| n
End of nested sub-routine; returns
to main subroutine.
If you run the subroutine (with its nested subroutine) alone using x = 4.3,
y = 7.9, z = 1.3, and t = 8.0, the answer you get upon pressing G.4 is
12.1074.