NOP (code)

In Ada, the null statement serves as a NOP.[6] As the syntax forbids that control statements or functions be empty, the null statement must be used to specify that no action is required. (Thus, if the programmer forgets to write a sequence of statements, the program will fail to compile.)

The second line below is an example of a single C statement that behaves like a NOP. In practice, most compilers will not generate code for this statement:

  int i = 0;
  i+1;

This statement performs an addition and discards the result. Indeed, any statement without side effects (and that does not affect control flow, e.g., break, return) can be removed, as the result of the computation is discarded.

The simplest possible statement in C that behaves like a NOP is the so-called null statement, which is just a semi-colon in a context requiring a statement. (A compiler is not required to generate a NOP instruction in this case; typically, no instructions whatsoever would be generated.)

  ;

Alternatively, an empty block (compound statement) may be used, and may be more legible:

  {}

In some cases, such as the body of a function, a block must be used, but this can be empty. In C, statements cannot be empty—simple statements must end with a ; (semicolon) while compound statements are enclosed in {} (braces), which does not itself need a following semicolon. Thus in contexts where a statement is grammatically required, some such null statement can be used.

The null statement is useless by itself, but it can have a syntactic use in a wider context, e.g., within the context of a loop:

  while (getchar() != '\n') {}

alternatively,

  while (getchar() != '\n')
      ;

or more tersely:

  while (getchar() != '\n');

(note that the last form may be confusing, and as such generates a warning with some compilers or compiler options, as semicolon usually indicates an end of function call instruction when placed after a parenthesis on the end of line).

The above code continues calling the function getchar() until it returns a \n (newline) character, essentially fast-forwarding the current reading location of standard input to the beginning of next line.

In Fortran, the CONTINUE statement is used in some contexts such as the last statement in a DO loop, although it can be used anywhere, and does not have any functionality.

The JavaScript language does not have a built-in NOP statement. Many implementations are possible:

• Use the ';' empty statement[7] or the '{}' empty block statement the same way as in the C and derivatives examples;
• Use the undefined or the null expression as a complete statement (an expression statement) when the previous methods are not allowed by the syntax.

Alternatives, in situations where a function is required, are:

• Use the Function.prototype() built-in function, that accepts any arguments and returns undefined;[8]
• Use a NOP function available in a third-party library —see below;
• Define a custom NOP function, as in the following example (using the ES6 arrow function syntax):

const noop = () => {};

The AngularJS framework provides angular.noop function that performs no operations.

The jQuery library provides a function jQuery.noop(), which does nothing.[9]

The Lodash library provides a function _.noop(), which returns undefined and does nothing.[10]

As with C, the ; used by itself can be used as a null statement in Pascal. In fact, due to the specification of the language, in a BEGIN / END block, the semicolon is optional before the END statement, thus a semicolon used there is superfluous.

Also, a block consisting of BEGIN END; may be used as a placeholder to indicate no action, even if placed inside another BEGIN / END block.

The Python programming language has a pass statement which has no effect when executed and thus serves as a NOP. It is primarily used to ensure correct syntax due to Python's indentation-sensitive syntax; for example the syntax for definition of a class requires an indented block with the class logic, which has to be expressed as pass when it should be empty.

The ':' [colon] command is a shell builtin that has similar effect to a "NOP" (a do-nothing operation). It is not technically an NOP, as it changes the special parameter $? (exit status of last command) to 0. It may be considered a synonym for the shell builtin 'true', and its exit status is true (0).[11][12][13]

The TeX typographical system's macro language has the \relax command.[14] It does nothing by itself, but may be used to prevent the immediately preceding command from parsing any subsequent tokens.[15]