The following are the major generic kinds of statements with examples in Pascal, a typical imperative language:
definition: TYPE SALARY = INTEGER
declaration: VAR A:INTEGER
assignment: A := A + 1
sequence: A := A + 1; WRITELN(A)
conditional: IF A > 3 THEN WRITELN(A) ELSE WRITELN("NOT YET") END
loop: FOR A:=1 TO 10 DO WRITELN(A) END
call: CLEARSCREEN()
Statements contrast with expressions in that the former do not return results and are executed solely for their side effects, while the latter always return a result and often do not have side effects at all.
In block-structured programming languages, statements are grouped into statement blocks.
Therefore, if any other I-O statement is executed for a file that has never been opened, no Declarative can receive control.
For example, an OPEN OUTPUT statement establishes a Declarative procedure for this file, and the file is then closed without error.
Error Handling: If there is an applicable file status clause (but not an applicable USE procedure) when an I-O error occurs, the file status is updated, and control returns to the program.
The program would work fine when asserts were enabled, but would fail when they were disabled, as it would no longer remove the null elements from the list.
The assert statement may, however, be used in conjunction with the "conditional compilation" idiom described in JLS 14.20, enabling the compiler to eliminate all traces of these asserts from the class files that it generates:
It is generally the case that programs using new facilities are not compatible with older releases.
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