Ada

In Ada, the null statement serves as a NOP.^[9] 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.)

C and derivatives

The simplest NOP statement in C is the null statement, which is just a semi-colon in a context requiring a statement.

Be aware that your C-compiler is going to ignore null statements, which has historical and performance reasons.

  ;

An empty block (compound statement) is also a NOP, and may be more legible, but will still be ignored by the compiler.:

  {}

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.

Fortran

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.

JavaScript

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

• Use the ; empty statement^[10] 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;^[11]
• 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 = () => {};

Pascal

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.

Python

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.

Shell scripting (bash, zsh, etc.)

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).^[14][15][16]

TeX macro language (ConTeXt, LaTeX, etc.)

The TeX typographical system's macro language has the \relax command.^[17] It does nothing by itself, but may be used to prevent the immediately preceding command from parsing any subsequent tokens.^[18]