Structured programming

Structured programming is a programming paradigm characterized by source code that uses block-based source code structure to encode control flow such as sequence, selection (i.e. if-then-else and switch) and iteration (i.e. for and while).

Originally, the central goal of the structured programming movement was to eliminate the need for and use of the goto statement. As goto provides powerful and flexible flow control, it can be used to write any arbitrarily complex algorithm, but the resulting code often has significant quality issues, commonly described as spaghetti code. Structured programming replaces goto with constructs that tend to result in better code. The paradigm became popular and for the most part achieved the goal of supplanting goto. In fact, its ubiquity is so thorough that for much of software development, it is simply the way code is written, no longer a topic of discussion as it once was.

Structured programming is sometimes associated with modular programming even though they are different. In a general sense, structured implies a sense of modularity and of being written to be efficient and easy to understand and modify, but this is not what structured programming means in a narrow sense.

After structured programming became popular, the style of programming that preceded it was retroactively called non-structured programming. Although technically a programming paradigm, it differs from other paradigms in that it was not intentionally designed. It was simply the state-of-the-art before structured programming was envisioned.