2.3 Scr0130: sequence, selection, and loop  (Page 2/9)

General background information

In this module, I will help you learn about:

• Structured programming.
• The sequence structure.
• The selection structure.
• The loop structure.

In introductory programming courses, you will often hear a lot about something called structured programming. In comparison with more modern and complex programming concepts such as runtime polymorphism, structured programming is fairly mundane. However, that's not to say that structured programming isn'timportant. It is very important. But it is just a small bump in theroad of learning that leads to a more complete understanding of computer programming, especially object-oriented programming.

What is structured programming ?

Basically, the concept of structured programming says that any programming logic problem can be solved using an appropriate combination of only threeprogramming structures, none of which are complicated. The three structures are known generally as:

• The sequence structure.
• The selection or decision structure .
• The loop, repetition, or iteration structure.

One door in and one door out

To understand structured programming, you need to think in terms of a section of program code that has only one entry point and one exit point. It isvery important that there cannot be multiple entry points or multiple exit points.

There must be only one way into the section of code and one way out of the section of code.

Nesting of structures is allowed

Another important part of the concept is that structures may be nested inside of other structures provided that every structure meets the basic rules for astructure.

Thus, by nesting simple structures inside of simple structures, large and complex overall structures can be constructed.

Pseudocode

Computer programming source code consists generally (but not in Scratch) of programming instructions written in text form with a very specific format or syntax that is designed to be understood by a computerprogram. Humans who are not computer programmers might not be expected to understand much of what they see in computer programming source code.

According to Wikipedia ,

"The prefix pseudo - (from Greek... "lying, false") is used to mark something as false, fraudulent, or pretending to be something it is not."

According to Wikipedia ,

"Pseudocode is an informal high-level description of the operating principle of a computer program or other algorithm. It uses the structural conventions of a programming language, but is intended for human reading rather than machine reading. Pseudocode typically omits details that are not essential for human understanding of the algorithm...

The purpose of using pseudocode is that it is easier for people to understand than conventional programming language code, and that it is anefficient and environment-independent description of the key principles of an algorithm."

The sequence structure

We can describe the sequence structure using the pseudocode shown in Image 1 .