What coding is and how software works

Every app on your phone, every website and every till at a supermarket runs on code: instructions written by people, in a language a computer can follow. Coding is not magic or genius. It is writing very clear, very precise instructions, then testing and fixing them until they work.

A program is a recipe

Think of a recipe for vetkoek: ingredients, then steps in order, with decisions ("if the oil is not hot enough, wait") and repetition ("fry each one until golden"). A program has the same parts:

• Data: the ingredients. Numbers, words, lists, prices, names.
• Steps: instructions carried out in order.
• Decisions: "if this, do that".
• Repetition: "do this for every item".

The difference is that a computer follows the recipe exactly as written. It never guesses what you meant, so the instructions must be precise.

How software runs

1. A programmer writes source code in a programming language, such as Python, JavaScript or Java.
2. A program called an interpreter or compiler turns that code into instructions the computer's processor can run.
3. The program takes input (a tap, a typed price, a file), processes it, and produces output (a total on screen, a message, a saved file).

The languages in this course

• Python (lessons 3 to 7 and 9): a clear, readable language used for automation, data, websites and AI. A good first language.
• HTML and CSS (lesson 8): the languages of web pages. HTML describes the content; CSS describes how it looks.

What programmers really do

Most of a programmer's day is not typing new code. It is:

• understanding the problem and the people who have it,
• breaking it into small steps,
• reading and fixing existing code (debugging),
• testing that it works for normal and unusual inputs,
• searching documentation and asking for help.

Making mistakes is normal. Error messages are clues, not failures.

Here is a first taste

This is a complete Python program. You will run one like it in the next lesson.

name = "Thandi"
print("Sawubona, " + name + "!")

It stores the word "Thandi" in a variable called name, then prints a greeting. Change the name, run it again, and the output changes. That is the core idea of programming.

A South African example

Sello works at a hardware store in Thohoyandou. Every Friday he spent two hours adding up sales from a spreadsheet export by hand. After learning basic Python, he wrote a 15-line program that reads the file, adds the sales per product and prints the top ten. The two-hour job now takes ten seconds, and he spends the time on customers instead.