Controlflow

Control flow, in computer science, refers to the order in which the computer executes statements in a program. It is governed by the syntax and semantics of the programming language and by the program’s runtime environment. The simplest form of control flow is sequential execution, where statements are executed one after another. Most programs modify this order with constructs that change the flow of control.

Selection constructs allow branching based on conditions. The most common forms are if-else statements and switch/case statements. Iteration constructs repeatedly execute a block of statements as long as a condition holds, with while and for loops being the typical examples. Loop control may be affected by break and continue statements or by language-specific features. Jump statements such as goto, return, or exception handling alter the normal sequence to transfer control to a different part of the program. Function calls introduce subroutines, and returns transfer control back to the caller. Recursion is an alternative where a function calls itself.

Dynamic control flow can also be influenced by events, asynchronous operations, or input from external sources. Modern languages provide asynchronous patterns such as callbacks, promises, futures, coroutines, or async/await, which allow the program to proceed without blocking and resume later.

In program analysis, control flow can be represented by a control flow graph, where nodes denote basic blocks and edges represent possible transfers of control. Such graphs enable optimizations, correctness proofs, and static analysis by illustrating all executable paths through a program.

Understanding control flow helps programmers reason about correctness, resource usage, and performance, and is fundamental to compiler design and program optimization.