A computer program is a list of "instructions" to be "executed" by the computer.
In a programming language, these program instructions are called statements.
x = 5;
y = 6;
z = x + y;
Values, Operators, Expressions, Keywords, and Comments.
Fixed values are called literals. Variable values are called variables.
The most important rules for writing fixed values are:
Numbers are written with or without decimals:
Strings are text, written within double or single quotes:
In a programming language, variables are used to store data values.
An equal sign is used to assign values to variables.
In this example, x is defined as a variable. Then, x is assigned (given) the value 6:
x = 6;
x = 5;
y = 6;
An expression is a combination of values, variables, and operators, which computes to a value.
The computation is called an evaluation.
For example, 5 * 10 evaluates to 50:
Expressions can also contain variable values:
The values can be of various types, such as numbers and strings.
For example, "John" + " " + "Doe", evaluates to "John Doe":
The var keyword tells the browser to create variables:
x = 5 + 6;
y = x * 10;
Code after double slashes // or between /* and */ is treated as a comment.
Comments are ignored, and will not be executed:
// var x = 6; I will NOT be executed
You will learn more about comments in a later chapter.
Identifiers are names.
The rules for legal names are much the same in most programming languages.
Subsequent characters may be letters, digits, underscores, or dollar signs.
Numbers are not allowed as the first character.
The variables lastName and lastname, are two different variables.
lastName = "Doe";
lastname = "Peterson";
Historically, programmers have used three ways of joining multiple words into one variable name:
first-name, last-name, master-card, inter-city.
first_name, last_name, master_card, inter_city.
FirstName, LastName, MasterCard, InterCity.
firstName, lastName, masterCard, interCity.
Unicode covers (almost) all the characters, punctuations, and symbols in the world.
For a closer look, please study our Complete Unicode Reference.