Engineering Craft › Clean Code & Principles

Structured Programming

Building programs from sequence, selection and loops instead of goto.

Also known as: structured code, goto considered harmful

Structured programming is the idea that programs should be built from three basic structures, instead of arbitrary jumps:

1. Sequence: statements run one after another.
2. Selection: choose a path (if, else, switch) (conditionals).
3. Iteration: repeat (for, while) (loops).

plus functions to name and reuse blocks. The point is that each piece has one entry and one exit, so you can understand it in isolation.

The problem it fixed

Early languages used goto to jump to any labeled line. Programs became tangled paths that could only be understood by tracing every jump, called spaghetti code. In 1968, Edsger Dijkstra wrote the letter “Go To Statement Considered Harmful” arguing for structured control flow instead.

10 IF X > 5 GOTO 50
20 PRINT "small"
30 GOTO 70
50 PRINT "big"
70 ...

becomes:

if x > 5:
    print("big")
else:
    print("small")

Today

Every mainstream language is structured, and goto is rare. You still meet its relatives:

• Early return, break and continue are limited, controlled jumps. They’re fine when they make code clearer (guard clauses).
• Exceptions jump out of nested code, which needs discipline (exceptions).
• Callbacks and async code can scatter control flow across places (callback hell).

The lasting lesson

Make the path through the code easy to follow: small functions, limited nesting (deep nesting), and clear structure. Complex, jumpy control flow is where bugs hide.