Definition
Control flow is the order in which the statements of a program are executed. The simplest control flow is purely sequential — one statement after another from top to bottom — but every nontrivial program also branches based on conditions, repeats blocks via loops, calls and returns from functions, and sometimes jumps to handlers when something goes wrong. Together these constructs describe every possible path the program could take from start to finish.
A small set of primitives is enough to express any computation: sequence, selection (if/else, switch), iteration (while, for), function invocation with return, and a mechanism for non-local jumps such as exceptions or early returns. Programming languages differ mostly in syntax, in which combinations they enforce, and in how they let you abstract control flow into reusable patterns.
Why it matters
How it works
At the machine level, control flow is implemented with a program counter that advances one instruction at a time, plus a small set of jump instructions that set the counter to a new address. Conditional jumps inspect a flag and branch if a comparison succeeded; unconditional jumps redirect execution unconditionally; call and return instructions manage a stack so functions can be nested and unwound. Everything above this — if, while, for, function calls, generators, coroutines — is built by the compiler from these primitives.
At the language level, the abstractions matter more than the implementation. A for loop binds an induction variable and a termination condition; a try/catch block declares a handler that will run if a downstream call throws; an await suspends a function and resumes it when a future completes. Each construct gives the reader a hint about what control will do, which is why disciplined use of structured control flow makes code easier to reason about than equivalent code dense with raw jumps. The cost of expressive control flow is that the number of distinct paths grows combinatorially — five independent conditions in a function yield thirty-two possible execution traces.