Smalltalk and Object Orientation: an Introduction - Free

ounded round to nearest truncate round down
In general, the arithmetic operators available in Smalltalk are essentially the sa me as in any other
language. For example, there is addition, subtraction, multiplication and division operators (+, -,*,/).
There are also comparison functions and truncation functions all of which are summarized in Table 7.1.
7.3 Characters and strings
7.3.1 Characters
Just like numbers, characters in Smalltalk are instances of an associated class. In this case the class
Character. Again we will consider this class and the operations it provides in greater detail later. For
the moment we will consider what characters look like. In Smalltalk, a single character is defined by
prefixing it with the $ (dollar) sign. For example:
$a $Z $@ $1 $$
All the above specify a single character, in this case the characters a, b, @, 1 and $.
7.3.2 Strings
Strings in Smalltalk are part of the Collection class hierarchy. As such they are made up of
individual elements in a similar manner to strings in C. However, this is the only similarity between C
strings and Smalltal k strings. Smalltalk strings do not need to be terminated by a null character, nor
should they be treated as arrays of characters. In Smalltalk, a string should be treated as an object in its
own right which responds to an appropriate range of messages (e. g. for manipulating or extracting
substrings).
In Smalltalk, a string is defined by one or more characters placed between single quotes. For
example:
'John Hunt' 'Tuesday' 'dog'
Note the use of single quotes rather than the double quotes used in some o ther languages (e.g. C and
Ada). This can be the source of much confusion and frustration when an apparently correct piece of
code will not work. Remember that double quotes indicate a comment in Smalltalk. Thus, the following
code will compile, but will generate a run time error:
a := "John Hunt".
This is because there is nothing to assign to the variable a as the comment “John Hunt” does not
return a value. Also be wary of assuming that a string containing a single character is equivalent to that
single character. It is not. For example:
'a' /= $a
The string ‘a’ and the character $a are instances of different classes, the fact that the string contains only
one character is just a coincidence. This can be particularly confusing for C programs as ‘a’ ind icates
the character a in C.
7.3.3 Symbols
Symbols are special strings which are always unique in the system. They do not respond to many of
the usual string manipulation messages, but they can be more efficient for some tasks than strings. A
symbol is indicated by a preceding hash (#). For example:
#john #Week #System42
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