Smalltalk and Object Orientation: an Introduction - Free

ifFalse: [.....]
However, it is easy to get confused and therefore one must be careful. A facility not provided
explicitly by Smalltalk is the if -then-elseif-else type of structure. For example, in C it is possible to
write:
if (n < 10)
printf (“less than 10”);
else if (n < 100)
printf (“greater than 10 but less than 100”);
else
printf (“greater than 100”);
In Smalltalk it is necessary to nest ifTrue:ifFalse constructs as above. However, it is easier to
see if you have a dangling else problem as the built -in formatter available in the various browsers can
be used to see if the code formats in the expected manner.
There is also no such thing as a case statement in Smalltalk. Instead, the fun ctionality required is
usually achieved using a dictionary.
map := Dictionary new.
map at: $^ put: [Transcript show: 'It is a caret'].
map at: $> put: [Transcript show: 'It is greater than'].
map at: $< put: [Transcript show: 'It is less than']
:
result := (map at: char) value.
This is the Smalltalk equivalent of the following in C:
switch (char) {
case '^':
printf(“It is a caret”);
break;
case: '>':
printf(“It is a greater than”);
break;
:
This is actually an example of how Smallta lk is truly object oriented. That is, even what would be
considered standard control structures in other languages, have to be implemented by using objects and
message passing. A point to note is that the control structures which do exist in Smalltalk may at first
seem to be similar to the control structures in other languages. However, this is both persuasive and
misleading. They are of course messages to objects (e.g. true, false or a block object). Internally they
perform something which is similar in na ture to what we have done above for the switch statement. If
you find this confusing, don’t worry, but if you can see what is meant by this then you have gone a long
way down the round to understanding Smalltalk.
9.4.2 Repetition
Iteration in Smalltalk is accomp lished with the timesRepeat:, whileTrue:, whileFalse: and
enumerating messages (such as do:). The enumerating messages will be considered in more detail when
we discuss the collection classes. For the moment we shall limit ourselves to a simple form of the do:
message and the timesRepeat message. In the next subsection we will consider the while -based
messages.
Like their counter -parts in other languages, the timesRepeat: and do: me ssages repeat a
sequences of instructions a fixed number of times. In C, this construct is provided by the for loop. For
example:
for (n = 1; n