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In computer programming, a sentinel value (also referred to as a flag value, trip value, rogue value, signal value, or dummy data) is a special value in the context of an algorithm which uses its presence as a condition of termination, typically in a loop or recursive algorithm.
first checks whether x is less than 5, which it is, so then the {loop body} is entered, where the printf function is run and x is incremented by 1. After completing all the statements in the loop body, the condition, (x < 5), is checked again, and the loop is executed again, this process repeating until the variable x has the value 5.
The following example of the policy file from "The Design and Implementation of Tripwire: A File System Integrity Checker" by Spafford and Kim makes use of the preprocessing language. Here it is used to ignore the directory with printer logs on a specific host, and this directory will be scanned on all other hosts.
The following example is done in Ada which supports both early exit from loops and loops with test in the middle. Both features are very similar and comparing both code snippets will show the difference: early exit must be combined with an if statement while a condition in the middle is a self-contained construct.
For example, in Python, to print the string Hello, World! followed by a newline, one only needs to write print ("Hello, World!" In contrast, the equivalent code in C++ [ 7 ] requires the import of the input/output (I/O) software library , the manual declaration of an entry point , and the explicit instruction that the output string should be ...
Loop unrolling, also known as loop unwinding, is a loop transformation technique that attempts to optimize a program's execution speed at the expense of its binary size, which is an approach known as space–time tradeoff. The transformation can be undertaken manually by the programmer or by an optimizing compiler.
Some languages may use a different naming convention for this type of loop. For example, the Pascal and Lua languages have a "repeat until" loop, which continues to run until the control expression is true and then terminates. In contrast a "while" loop runs while the control expression is true and terminates once the expression becomes false.
In 1964, the expression READ-EVAL-PRINT cycle is used by L. Peter Deutsch and Edmund Berkeley for an implementation of Lisp on the PDP-1. [3] Just one month later, Project Mac published a report by Joseph Weizenbaum (the creator of ELIZA, the world's first chatbot) describing a REPL-based language, called OPL-1, implemented in his Fortran-SLIP language on the Compatible Time Sharing System (CTSS).