programming-for-dummies

222
Passing Parameters
The second command doesn’t work because the PrintMyName subprogram
expects an integer first and a string second, but this command gives it the
data in the wrong order.
If a subprogram doesn’t need any parameters, you can just call that subprogram
by using its name, such as
PrintMyName
If you aren’t passing any parameters in some programming languages, you
must leave the parameter list (the stuff between the parentheses) blank,
such as
printMyName ();
Passing parameters by reference
When a program calls and passes parameters to a subprogram, the computer
makes duplicate copies of those parameters. One copy of those parameters
stays with the main program and the second copy gets passed to the
subprogram.
Now if the subprogram changes those parameters, the values of those
parameters stay trapped within the subprogram, as shown in Figure 6-6.
Main program
Subprogram
Figure 6-6:
Normally
when you
pass
parameters
to a
subprogram,
the
computer
makes a
second
copy for the
subprogram
to use.
X = 9
Y = 35
ChangeMe (X, Y)
Print ”X value = ”; X
Print ”Y value = ”; Y
This prints:
X value = 9
Y value = 35
SUB ChangeMe (A as Integer, B as Integer)
A = A + 7
B = B + A
Print ”A value = ”; A
Print ”B value = ”; B
END SUB
This prints:
A value = 16
B value = 51
When passing parameters by value, any changes the
subprogram makes to the parameters won’t be sent back to
any other part of the program.