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The repeat statement repetitively executes a block of one or more statements through an until statement and continues repeating unless the condition is false. The main difference between the two is the while loop may execute zero times if the condition is initially false, the repeat-until loop always executes at least once.
The structured program theorem, also called the Böhm–Jacopini theorem, [1] [2] is a result in programming language theory.It states that a class of control-flow graphs (historically called flowcharts in this context) can compute any computable function if it combines subprograms in only three specific ways (control structures).
Executing a set of statements only if some condition is met (choice - i.e., conditional branch) Executing a set of statements zero or more times, until some condition is met (i.e., loop - the same as conditional branch) Executing a set of distant statements, after which the flow of control usually returns (subroutines, coroutines, and ...
Do-while(0) statements are also commonly used in C macros as a way to wrap multiple statements into a regular (as opposed to compound) statement. It makes a semicolon needed after the macro, providing a more function-like appearance for simple parsers and programmers as well as avoiding the scoping problem with if.
At the level of functions, this is a return statement. At the level of loops, this is a break statement (terminate the loop) or continue statement (terminate the current iteration, proceed with next iteration). In structured programming, these can be replicated by adding additional branches or tests, but for returns from nested code this can ...
Some CFG examples: (a) an if-then-else (b) a while loop (c) a natural loop with two exits, e.g. while with an if...break in the middle; non-structured but reducible (d) an irreducible CFG: a loop with two entry points, e.g. goto into a while or for loop A control-flow graph used by the Rust compiler to perform codegen.
Pseudocode is commonly used in textbooks and scientific publications related to computer science and numerical computation to describe algorithms in a way that is accessible to programmers regardless of their familiarity with specific programming languages.
Nassi–Shneiderman diagrams reflect this top-down decomposition in a straightforward way, using nested boxes to represent subproblems. Consistent with the philosophy of structured programming, Nassi–Shneiderman diagrams have no representation for a GOTO statement. Nassi–Shneiderman diagrams are only rarely used for formal programming.