ElmoMC SimplIQ Software Manual - Manual (Page 57)

SimplIQ Software Manual 4BThe SimplIQ User Programming Language
MAN-SIMSW (Ver. 1.4)
5-28
This code executes the sequence:
JV=1000;IA[1]=1;BG;
After executing JV=1000, the program jumps to the subroutine JustSo. Before doing so, it
stores its return address, which is the place in the code at which execution should resume
after the routine is complete. In this example, the return address is the line number of
instruction BG, which is just after the subroutine call.
The return command instructs the program to resume from the stored return address. After
execution is resumed at that address, it is no longer required and is no longer stored.
Functions may call each other; in fact they may even call themselves. Return addresses for
nested function calls are stored in a call stack, as shown in the following example:
function factorial();
Function prototype.
…
IA[1]=3
IA[2]=1
factorial()
Function call.
BG
…
function factorial()
Function for factorial.
global int IA[];
Define array as global inside function.
IA[2]=IA[2]*IA[1]
Recursive algorithm.
IA[1]=IA[1]-1
if (IA[1]>1) factorial() ; end
Recursive call.
return
Function end
The factorial function in this example calculates the factorial of 3 in IA[2]. The variable IA[1]
counts how many times the function factorial is executed.
The program executes as follows:
Code IA[1] IA[2] Call Stack
IA[1]=3
3 Undefined Empty
IA[2]=1
Unchanged 1 Empty
factorial
Unchanged Unchanged →BG
IA[2]=IA[2]*IA[1]
Unchanged 3 Unchanged
IA[1]=IA[1]-1
2 Unchanged Unchanged
if (IA[1]>1)
factorial(); end
Unchanged Unchanged →RT
→BG
IA[2]=IA[2]*IA[1]
Unchanged 6 Unchanged
IA[1]=IA[1]-1
1 Unchanged Unchanged
if (IA[1]>1)
factorial(); end
Unchanged Unchanged Unchanged (condition is false)
return
Unchanged Unchanged →BG (program jumps to
return on top of call stack)
return
Unchanged Unchanged Empty (program jumps to BG
on top of call stack)
BG
Unchanged Unchanged Unchanged