36 §In many languages (as in Java) you can choose whether a procedure (called a methodin O-O languages) has a return value or not §If it does have a return value, then you will often see calls to it like chr = firstCharOf( str); so the return value of the procedurefirstCharOf() is assigned to the variable chr Or, calls like print( firstCharOf( str )); Return Types
37
§
So the return value of
firstCharOf()
is given to
the procedure
print()
§
In typed languages like Java (which require you
to declare the type of variables) you will need to
declare the return type of a procedure in its
definition and make sure it makes sense where
it is called
§
In some languages procedures with return
values are called
functions
Return Types
38 §In the definition of a procedure with a return value you will need to indicate exactly which value to return to the main program or another procedure. For example, in Java you write: return 2; to immediately send the value 2 back from the procedure §Use "return value" also in pseudo-code. Make sure that the type of the value matches the declared return type of the procedure Return Types
39
§
Here is the possible pseudo-code for the whole
of the procedure
lastCharOf()
Procedure char lastCharOf( String str )
n = lengthOf(str)
lco = CharAt( str, n-1 )
return lco
§
Again this is high-level
§
However, I happen to know that it uses procedures
which are (practically) built-in to Java
§
They find the length of a String and find the
character at a given index location in a String
Example
40
§
As in many languages, Java indexes String
(and Array) locations starting from 0
§
So the first character is at index 0, etc.
§
If you want to know how these procedures
themselves are defined in terms of even more
basic steps then you need to start thinking
about the way Strings are implemented
§
But that is Data Abstraction and it is looking below
Java anyway, so we won’t
Example
41
§
Note there is no official syntax (way of writing)
procedures in pseudocode, but do try to be
clear about names, types, etc.
Example
42
§
If the procedure has no return value then it can
only be called via a whole statement like:
print(‘x’);
or
print( firstCharOf( str ) );
i.e. it does
not
make sense to write
a = print(‘x’);
§
In Java these types of procedures are treated
in a similar way to procedures with a return
value. We just declare the return type to be
void
if we have no return value
Procedures With No Return Types
43
§
You can put a
return
statement in the definition
of the procedure to indicate where control
passes back to the main program
§
Remember that code might (or might not) be
useless after a return statement:
void proCC( int
x) {
if (x != 3) {
x = 4;
}
else
return;
Procedures With No Return Types
44
printOut(x);
return;
printOut(x-1);
} //end of proCC
§
Sometimes, you do not have to put a
return
§
The procedure also returns when its end is reached
Procedures With No Return Types
45
§
Information is also passed in and out of a
procedure via its arguments
§
You will need to specify the number of, types of
and exact ordering of arguments
§
You do this in the procedure definition by using
some
formal parameters
, i.e. variables
standing for the arguments (actual parameters)
which you can then use in the body of the
procedure
Formal Parameters and Arguments
