1.3 Scr0330: sequence, selection, and loop in scratch 2.0.  (Page 2/9)

Images

• Image 1 . The sequence structure in pseudocode.
• Image 2 . The selection structure in pseudocode.
• Image 3 . The loop structure in pseudocode.
• Image 4 . Scratch 2.0 programming interface for the program named IfSimple01.
• Image 5 . A paraphrased version of the Scratch code.
• Image 6 . Program code for the left beachball
• Image 7 . Initializing the position and orientation of the basketball.
• Image 8 . All of the code that applies to the basketball.
• Image 9 . Pseudocode for a selection structure.
• Image 10 . Two independent decisions.
• Image 11 . Control structures available in Scratch.
• Image 12 . Programming blocks belonging to the Sensing group.
• Image 13 . Initial output from the program named IfWithVar01.
• Image 14 . Program output after having clicked twice in the Stage area.

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 the road of learning that leads to a more complete understanding of computerprogramming, 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. (This is commonly called source code.) 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."