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declarations
summary
This subchapter looks at declaring variables.
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This subchapter looks at declaring variables.
free computer programming text book projecttable of contents
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This subchapter is a stub section. It will be filled in with instructional material later. For now it serves the purpose of a place holder for the order of instruction.
Professors are invited to give feedback on both the proposed contents and the propsed order of this text book. Send commentary to Milo, PO Box 1361, Tustin, California, 92781, USA.
This subchapter looks at declaring variables.
Variables are named with identifiers. In most languages variables may be given any valid identifer name.
Variables may have any valid identifier name in C.
Variables may have any valid identifier name in Pascal.
Variables may have any valid identifier name in PL/I.
Some languages require that variables be explicitly declared, while other languages allow an implicit declaration.
Variables should be explicitly declared by type in C. Variables without a type specification default to extern int.
Variables must be explicitly declared in Pascal.
Undeclared variables that start with the letters I through N, inclusive, (short for INteger) are assumed to be integers, while all other undeclared variables are assumed to be floating point.
Undeclared variables that start with the letters I through N, inclusive, (short for INteger) are assumed to be integers, while all other undeclared variables are assumed to be floating point.
Some languages require that variables be declared in a specific portion of the program, while others allow variable declarations to be scattered through a program (but usually still must be before first actual use).
C variables may appear in any of several recommended locations. Variables declared in unusal locations may exhibit strange or unpredicatable behavior. Recmmended locations include the beginnings of source files or translation units, beginnings of functions, and beginnings of blocks.
Pascal variables must be declared in the declaration part, which comes immediately before the statement part.
program SimpleProgram (output);
var Age: Integer;
begin
Age := 21;
write ('Susan is ');
write (Age);
writeln (' years old.')
end.
Note that outputting a variable involves giving the name of the variable without any apostrophes (quotation marks).
The output of this program would be:
Susan is 21 years old.
end.
“21 The body of a program unit generally contains two parts: a declarative part, which defines the logical entities to be used in the program unit, and a sequence of statements, which defines the execution of the program unit.” —:Ada-Europe’s Ada Reference Manual: Introduction: Language Summary See legal information
“22 The declarative part associates names with declared entities. For example, a name may denote a type, a constant, a variable, or an exception. A declarative part also introduces the names and parameters of other nested subprograms, packages, task units, protected units, and generic units to be used in the program unit.” —:Ada-Europe’s Ada Reference Manual: Introduction: Language Summary See legal information
The format for a declaration varies by programming language.
In C the order of the parts of a declaration are: a list of storage class specifiers (such as register), type specifiers (such as int), and type qualifiers (such as const), a list of names of variables, an optional equal sign and initialization value, and the semicolon separator.
extern int age = 21;
In Pascal the order of the parts of a declaration are: the reserved word var, the name of the variable, a colon character ( : ), the type of the variable, and the semicolon terminator.
var Age: Integer;
In almost all languages each variable may be declared on a separate line.
In many languages it is possible to declare several variables of the same type in a single declaration.
In C it is possible to declare multiple variables in the same declaration as long as they all share the exact same specifiers and qualifiers. In this case the variable identifier names will be separated by a comma.
int RunningSubTotal, FinalTotal
In Pascal it is possible to declare multiple variables in the same declaration as long as they all share the exact same type. In this case the variable identifier names will be separated by a comma.
var RunningSubTotal, FinalTotal: integer;
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