Programming
What Is …
It is important to distinguish between programming, software engineering (software development) and computer science. Although it is difficult to agree on brief universal definitions, I would say that the difference between them is comparable to the difference between masonry, architecture (house building) and physics. Although software is very much different from houses.
Programming
Programming involves mainly writing an actual programming code, it is more of a craft. Programming is something you can learn best by exercise and practice and by reading other peoples’ code. Programing skills are often tied to a single programming language – i.e. an excellent programmer in one language may be really poor in another language. The asset of a good programmer is speed and code quality – made possible by deep understanding of the technology she uses. Anyone (with a little effort) can learn to write computer programs. The skill is in being able to do it efficiently and with reasonable quality – the same way as anyone (with a little effort) can build a brick wall.
Software Engineering
Software Engineering (as any other engineering) deals with the question how the programming code should be organized and what development processes should be applied. Software development includes a great deal of Project management and it is something you learn best by studying rules and standards and by learning from (preferably other peoples’) failed projects. Software engineering guides programmers in writing their code in a similar manner in which architectural plans guide masons. Software engineering requires a broad understanding of many technologies and approaches so that you can choose the most suitable ones for the assignment.
Computer Science
Computer Science is the theoretical foundation of it all. It defines how each of the used technologies behaves, and why it behaves that way. Learning computer science involves the study of various fields of mathematics (set theory, graph theory, etc.) and logic. Knowing parts of Computer Science is very useful for a Software Engineer as she then knows what are the basic inherent properties of technologies she is using.
Programming for Dummies
If you haven’t done any programming yet, this part is for you, otherwise skip for the next part. This is not an introduction to computer science or theory of formal languages. It is an introduction for beginner programmers, so that they know about all the crucial concepts.
Computers are in a way very stupid. The core of a computer is a processor (CPU) and a memory. The processor is capable of carrying out simple instructions (e.g. “add these two numbers together”). The memory can be either volatile (typically RAM) or permanent (typically hard drive). Then there is a bunch of Input/Output devices such as a graphic card and display, keyboard, mouse, etc.
To make the processor do something, you need to provide it with a (computer) program. The program is executed on the processor by following the instructions written in the program. A program is created by writing a source code in a particular programming language. Since the processor understands only low-level instructions, the programming language also has to be low-level (such as the Assembly language).
Using a low-level programming language is a very tedious task, so the computer is equipped with an Operating system (OS), which provides much broader functionality and takes care of a lot of the dirty work for us. The operating system understands higher level commands such as ‘save a file’ or ‘show this text on the screen’, etc. and makes it possible to use a high-level programming language.
Source Code
A source code is a simple text document, which contains the instruction for the operating system (and
subsequently the processor) to perform.
In a high-level language, the source code must be translated into more low-level instructions the OS and the processor
understands. This is done usually either by compiling or interpreting. In a compiled language
(e.g. C++), the
source code is translated to an executable file.
An executable file is simply a file you can execute, e.g. on Windows, everything with .exe extension.
In an interpreted language, you need to run another program – the Interpreter – which reads
your source code from a text file, interprets what it’s supposed to do, and instructs the OS or processor to do that.
There are a lot of exceptions to the above, including languages like
Java or
C# which are somewhat partially compiled.
However most of the languages widely used in Web application development are interpreted.
A Source code is a plain-text document which is written using the chosen programming language. A programming language is an artificial language (formal language. The rules by which the language is defined are called syntax. In natural languages (such as English), such rules do not have to be followed strictly (and you can still be understood). However in programming languages, the syntax must be followed strictly and precisely, otherwise the interpreter or compiler is not able to process (parse) the source code. Strictly speaking, first the interpreter parses the source code to try to understand what you have written, and then evaluates that by making the operating system and processor do something.
There are big differences between different programming languages, but there are also some things which are common for all languages – language elements, type system and standard library.
Language Elements
The syntax of each programming language is different. The syntax rules define where and how various special characters (which denote the language elements) should be written. I will give the following examples in PHP, because you will use it later anyway. Most languages have the following language elements:
- comments
- literals
- constants
- variables
- operators
- expressions and statements
- control flow constructs
- conditions
- loops
- functions, classes & objects
- keywords
Comment
Comments are part a of the programming language, but they are not interpreted in any way. They serve the purpose of writing your comments to the source code.
<?php
// this is a comment, and does nothing
Comments are either single-line or multi-line. A single-line comment (the above example) runs until the end of the line. A multi-line comment must be terminated by a sequence of characters.
<?php
/* this is a comment, that
does nothing and spans over more lines.
*/
Literal
These are values written directly in the code. For example, when you write in PHP:
<?php
echo "Hello World!";
The text Hello World! is a text literal. The echo part is command which makes sure, that the
text is printed.
Constant
These are values also written in the code, but they are assigned a name. For example:
<?php
define('MONTHS_IN_YEAR', 12);
echo MONTHS_IN_YEAR;
The MONTHS_IN_YEAR is a constant (value that does not change) and has a name MONTHS_IN_YEAR.
In this case, the constant value was defined using a define() function.
Variables
Variables are one of the most important parts of a programming language. For example in PHP:
<?php
$name = 'Jane';
echo $name;
$name = 'John';
echo $name;
The above will first print Jane and then John. Variables in PHP are marked with the $ sign,
so the $name is a variable. Technically, a variable is actually a space in computer memory.
The variable can contain different values in time.
Operators
Each language has operators for working with values. For example:
<?php
echo 4 + 5;
The above will print 9. + is an arithmetic operator. Each language has standard arithmetic
operators such as -, +, *, /. Then there are other operators – for example boolean operators for
working with boolean values. By the way, 4 and 5 are literals.
Expressions and Statements
Expressions are language constructs which yield a value (can be evaluated). For example, in the above
case 4 + 5 is an expression, which yields a value 9. Expressions can be
simple or compound. Compound expressions should use parentheses to determine explicitly
the order of evaluation. E.g.
<?php
echo (4 + 5) * 10;
The above will print 90. The order of expression evaluation is particularly
important for boolean expressions. Also note that echo is not part of the expression,
it is a command which prints a value to the screen. The value is obtained by evaluating the expression.
Control Flow
Control flow structures are language constructs which control the flow of the program. These are mainly conditions and loops. They control what lines of the source code get executed:
<?php
$what = 5
if ($what > 0) {
echo "5 is bigger than 0";
}
An if condition can have multiple branches:
<?php
$what = 5
if ($what > 0) {
echo "5 is bigger than 0";
} else {
echo "5 is smaller than 0";
}
Functions, classes and objects
Functions and Classes are language tools which help you organize the source code more efficiently, reduce repetition and generally make things less tangled and confusing. Each language has many built in functions.
Keywords
Keywords are reserved words of the language. They have some special meaning in the
language itself and do something special. E.g. in the above examples, the keyword
if marks the beginning of a conditional statement. The keyword echo prints
a text to the screen.
Type System
The source code must strictly conform to the defined syntax of the chosen language. Apart from the syntax, there are other rules, a very important one is Type System. The values used in a programming language can have different data types. These types are specific to each language, but there are some commonly used:
- boolean – A value which is either true or false.
- integer – A whole number.
- string – A string of characters – i.e. a text.
- float, real – A decimal number
- array – A List of values (each value can be of the above type)
Depending on how the language handles its types, there are strongly typed languages and weakly (loosely) typed languages. Because this is quite a complicated area, I will simplify it to just that in a weakly typed language, the values of different types are converted automatically. In a strongly typed language, the values must be explicitly converted. Most languages used in web application development are weakly typed which means that you can write e.g.:
<?php
echo 5 + '4';
In the above example, the '4' gets automatically converted to an integer, so that
it can be added to the integer 5. Then the output 9 is converted to a string '9' which
is printed to the screen. The following code will fail:
<?php
echo 5 + 'four';
The above would yield an error, because the language interpreter is stupid and does not know that
the string four can be converted to the number 4.
Boolean Type
A boolean data type has only two values: true and false. The boolean type is of great significance in programming. The boolean values (true, false) are also called logical values. They can be manipulated using logical operators (part of boolean logic or boolean algebra). The most important logical operators are:
- logical and (conjunction) – the result value is true if both operands are true, otherwise it is false.
- logical or (disjunction) – the result value is true if either operand is true, otherwise it is false (i.e. if both operands are false)
- logical not (negation) – the result is negation of the value (if one operand is true, the result is false and vice versa).
The and and or operators are binary which means that they have two operands. While it may sound alien,
you are already familiar with binary operators. E.g. if you write 4 + 3. The plus + is a binary
operator (arithmetic, not boolean though), 4 and 3 are its operands. The result is 7.
Similarly you can write true and false. The and is a binary boolean operator, true and false are
its operands. The result is false. The not operator is unary which means that it has only one operand.
For example the expression not true, negates the value true and results false. This is sort of logical, isn’t it?
That’s why it’s called boolean logic :). In PHP, the not operator is written using the exclamation mark !:
Some examples:
!true; // -> yields false
(true and true) or false; // -> yields true
((true or false) and true) and (!true); // -> yields false
(!((!true) or false)) or false; // -> yields true
Knowing how boolean operators work is essential for writing conditional statements.
Standard Library
A part of each high-level language is a function library (library or standard library). A library is a collection of generally usable functions and blocks which you can use in the source code of that language. The library provides even higher level functions then those the language itself has. E.g. it could be functions for ciphering, sending data over network, user interface controls, etc. The problem is that each programming language has its own library, and each library contains thousands of functions. Therefore it is very time consuming to get yourself acquainted with the language library. Contrary to popular belief, a programmer spends most of his time reading manuals for the libraries.
Apart from a standard library which comes bundled with every language interpreter (or compiler), there are also many 3rd party libraries. In general, the term library represents an external set of functions which we (as programmers) include in our application without modification. There are also other terms describing a set of functions like packages, modules, extensions, plugins. In principle, all these represent the same thing.
Summary
In this article, you have learned the basic programming jargon. If you do not feel confident having intuitive understanding of the terms below, try to take a course at Codecademy which should help you digest them better.
It is very important to understand that the source code is executed so that each statement is executed sequentially – usually only one statement is written per line (for readability), therefore, the source code is executed line-by-line (unless control-flow structures change the program flow). This in essence describes how computer programs are made to run. Perhaps you wonder what is the difference between a program and an application. Well the best I’m aware of is that an application is a program, which has a user interface. So unless you are working on some low level programs (e.g. device drivers), you’re making an application.
New Concepts and Terms
- programming
- software development, software engineering
- computer science
- developer
- source code
- volatile/permanent memory
- programming language / formal language
- compiler
- interpreter
- parser
- execution
- expression
- statement
- code evaluation
- type system
- standard library
- strong type system
- weak type system
- comments
- literals
- constants
- variables
- operators
- operand
- binary operator
- unary operator
- control flow constructs - conditions, loops
- integer
- string
- float / real
- arrays