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no operation/null statement
summary
This subchapter looks at the null statement or no operation.
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This subchapter looks at the null statement or no operation.
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 the null statement or no operation.
It may seem strange to have a staement that doesn’t do anything, but it actually is useful.
Soon you will encounter control structures that must have a statement or block of staements in a particular position. The null statement can be used to fill this requirement when the programmer has no actual coding that can usefully fill that location.
The semicolon (;) performs no action and serves as a placeholder in C. It is called the null statement.
;
The semicolon (;) performs no action and serves as a placeholder in Pascal. It is called the empty or null statement.
;
The NULL statement performs no action and serves as a placeholder in Ada. It is called the null statement.
NULL;
The CONTINUE statement performs no action and serves as a placeholder in FORTRAN. It is called the continue statement.
CONTINUE
TThe semicolon (;) performs no action and serves as a placeholder in PL/I. It is called the null statement.
;
The null statement may have a label:
ALABEL:;
When used on the ELSE of an IF THEN ELSE structure, it is called the Null Else.
ELSE;
The pass statement performs no action and serves as a placeholder in Python. It is called the pass statement.
pass
As a historical note, the no operation command appears in most computer or processor instruction sets and can be duplicated in almost all by some kind of clever programming. In the early days of computers, before structured programming and at a time when it was common to manually load programs with front panel switches, programmers would use the no operation command during testing and debugging. An existing command or commands could be temporarily “commented out” by replacing them with no operations. Alternatively, extra no operations could be inserted into strategic spots in a program to intentionally reserve space for alternate (longer) sequences of code. On computers where the binary operation command (object code) for the no operation was all zeros, it could also be used to initialize large areas for either data or code purposes with a value that was both a safe operation code and a safe initial data value.
Coding example: I am making heavily documented and explained open source code for a method to play music for free — almost any song, no subscription fees, no download costs, no advertisements, all completely legal. This is done by building a front-end to YouTube (which checks the copyright permissions for you).
View music player in action: www.musicinpublic.com/.
Create your own copy from the original source code/ (presented for learning programming).
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Created: March 31, 2011
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