Programming Fundamentals › Programming Basics
Control Flow
The order in which statements execute: branches, loops, returns.
Also known as: flow of control, program flow, execution order, flow control
Control flow is the order in which a program’s statements run. By default, lines run top to bottom. Control flow structures change that order.
| Structure | What it does | Examples |
|---|---|---|
| Sequence | One statement after another | the default |
| Branching | Choose a path | if/else, switch, ternary |
| Loops | Repeat | for, while |
| Jumps | Leave early or skip | return, break, continue |
| Function calls | Go into another function, then come back | functions |
| Exceptions | Jump out when something goes wrong | try/except, throw |
def first_negative(numbers):
for n in numbers: # loop
if n < 0: # branch
return n # jump out early
return None # reached only if no negative was foundReading code by following the flow
When debugging, ask: which path did execution take? Add a print or use a debugger to step through, and see which branches ran and which loops repeated.
Habits
- Keep it simple. Deep nesting and many exits are hard to follow. Use guard clauses to handle special cases early.
- Make every branch intentional: what if none of the conditions match?
- Avoid hidden flow: exceptions and callbacks make the path less visible, so document them.
- Watch loops for exits: an infinite loop is a flow with no way out.
Asynchronous code adds another kind of flow, where work continues later (async/await).