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In 1959, Douglas E. Eastwood and Douglas McIlroy of Bell Labs introduced conditional and recursive macros into the popular SAP assembler, [36] creating what is known as Macro SAP. [37] McIlroy's 1960 paper was seminal in the area of extending any (including high-level ) programming languages through macro processors .
It was extended shortly after, firstly by Mike Lesk and then by John Reiser, to add arguments to macros and to support conditional compilation. [4] The C preprocessor was part of a long macro-language tradition at Bell Labs, which was started by Douglas Eastwood and Douglas McIlroy in 1959. [5]
The definition of the list's elements. Expansion(s) of the list to generate fragments of declarations or statements. The list is defined by a macro or header file (named, LIST) which generates no code by itself, but merely consists of a sequence of invocations of a macro (classically named "X") with the elements' data.
For #include guards to work properly, each guard must test and conditionally set a different preprocessor macro. Therefore, a project using #include guards must work out a coherent naming scheme for its include guards, and make sure its scheme doesn't conflict with that of any third-party headers it uses, or with the names of any globally visible macros.
If-then-else flow diagram A nested if–then–else flow diagram. In computer science, conditionals (that is, conditional statements, conditional expressions and conditional constructs) are programming language constructs that perform different computations or actions or return different values depending on the value of a Boolean expression, called a condition.
A conditional sentence is a sentence in a natural language that expresses that one thing is contingent on another, e.g., "If it rains, the picnic will be cancelled." They are so called because the impact of the sentence’s main clause is conditional on a subordinate clause.
A high-level illustration showing the decomposition of machine instructions into micro-operations, performed during typical fetch-decode-execute cycles [1]: 11 . In computer central processing units, micro-operations (also known as micro-ops or μops, historically also as micro-actions [2]) are detailed low-level instructions used in some designs to implement complex machine instructions ...
the conditional operator can yield a L-value in C/C++ which can be assigned another value, but the vast majority of programmers consider this extremely poor style, if only because of the technique's obscurity.