Rice Lake iRite IDE - Manual (Page 10)

6 920i Programming Reference
2.2 Program Example with Constants and Variables
The “Hello, world!” program didn’t use any explicitly declared constants or variables (the string “Hello, world!”
is actually a constant, but not explicitly declared). Most useful programs use many constants and variables. Let’s
look at a program that will calculate the area of a circle for various length radii. The program, named
“PrintCircleAreas”, is listed below.
01 program PrintCircleAreas;
02
03 -- Declare constants and aliases here.
04 g_ciPrinterPort : constant integer := 2;
05
06 -- Declare global variables here.
07 g_iCount : integer := 1;
08 g_rRadius : real;
09 g_rArea : real;
10 g_sPrintText: string;
11
12
13 function CircleArea(rRadius : real) : real;
14 crPie : constant real := 3.141592654;
15 begin
16 -- The area of a circle is defined by: area = pie*(r^2).
17 return (crPie * rRadius * rRadius);
18 end;
19
20
21 begin
22
23
for g_iCount := 1 to 10
24 loop
25
26 g_rRadius := g_iCount;
27 g_rArea := CircleArea(g_rRadius);
28
29
g_sPrintText := "The area of a circle with radius " + RealToString(g_rRadius, 4, 1)
30 + " is " + RealToString(g_rArea, 7, 2);
31
32
WriteLn(g_ciPrinterPort, g_sPrintText);
33
34
end loop;
35
36 end PrintCircleAreas;
The PrintCircleAreas program demonstrates variables and constants as well as introducing these important ideas:
for loop, assignment statement, function declarations, function calling and return parameters, string
concatenation, WriteLn procedure, a naming convention, comments, and a couple of data conversion functions.
You probably know by now that this program will calculate the areas of circles with radius from 1 to 10
(counting by 1s) and send text like, “
The area of a circle with radius 1 is 3.14 ,” once for each radius, out the
communication port 2.
01 program PrintCircleAreas;
Line 1 is the program header with the keyword program and the program identifier “PrintCircleAreas”. This is
the same in theory as the “HelloWorld” program header.
Line 3 is a comment. In iRite all comments are started with a -- (double dash). All text after the double dash up
to the end of the line is considered a comment. Comments are used to communicate to any reader what is going
on in the program on the specific lines with the comment or immediately following the comment. The -- can
start on any column in a line and can be after, on the same line, as other valid program statements.