BASIC Programming

Anybody can write a program. A background in mathematics or science is not required. Patience, practice, and an interest in the subject matter should suffice, along with the required software and hardware.
Understanding programs can appear daunting at first, but their reliance on logical operations allow for easy learning of commands which you will commonly see in many programs.
A program itself is merely a series of commands in the order in which they are to be executed. That is to say, that the first line is the beginning of the program!
All programs a user uses from day to day, including browsers (Internet Explorer, Firefox, etc.) and operating systems (Windows, *nix and MacOS) are separate sets of lines of code, which aim to fulfill tasks. the amount of code is dependent on how simple the task generally, and different types of code may be used for the advantages they give. BASIC is considered an excellent starting point for moving onto other languages, and can be useful for simple programs.

Programming Languages

Programming languages allow people to give instructions to a computer with commands that both the computer and the programmer can understand. Different programming languages use different commands and different rules for entering those commands; similar to the way people speak different words to each other with the same meaning. One person may say "hello", while another says "hola", which, although express the same thought, appear different.
Similarly other human languages, such as French and Spanish, are similar to each other, as computer programming languages can be also. Programming languages that are similar are usually referred to as related languages. Once a person learns a programming language, it is easier to then learn other programming languages especially those related to the first one, as many similarities in structure are shared between languages, especially those with a common ancestor.

The language taught here, BASIC, is easier to learn than others as its commands are similar to English and has a simple set of rules for entering them.

JavaScript

JavaScript is the most popular programming language in the world.

JavaScript is the programming language of the Web.
All modern HTML pages are using JavaScript.
JavaScript is easy to learn.

In HTML, JavaScript code must be inserted between <script> and </script> tags.

Example

<script>
       document.getElementById("demo").innerHTML = "My First JavaScript";
</script>

 JavaScript Programs

A computer program is a list of "instructions" to be "executed" by the computer.
In a programming language, these program instructions are called statements.
JavaScript is a programming language.
JavaScript statements are separated by semicolon.

Keywords or Reserved Words (like College, Car, Male, Company)

In JavaScript, some identifiers are reserved words and cannot be used as variables or function names.

JavaScript keywords are used to identify actions to be performed.

The var keyword tells the browser to create a new variable:

var x = 5 + 6;
var y = x * 10;

Identifiers (like Indira, Mercedes, Dinesh,  Aptara)

Identifiers can be short names (like x and y), or more descriptive names (age, sum, totalVolume).
The general rules for constructing names for variables (unique identifiers) are:

• Names can contain letters, digits, underscores, and dollar signs.
• Names must begin with a letter
• Names can also begin with $ and _ (but we will not use it in this tutorial)
• Names are case sensitive (y and Y are different variables)
• Reserved words (like JavaScript keywords) cannot be used as names

In HTML, JavaScript programs can be executed by the web browser.

JavaScript Statements

JavaScript statements are composed of:

Values, Operators, Expressions, Keywords, and Comments.

JavaScript Values

The JavaScript syntax defines two types of values: Fixed values and variable values.

Fixed values are called literals. Variable values are called variables.

JavaScript Literals

The most important rules for writing fixed values are:

Numbers are written with or without decimals:

10.50

1001

 Strings are text, written within double or single quotes:

"John Doe"

'John Doe'

 Expressions can also represent fixed values:

5 + 6

5 * 10

JavaScript Variables

In a programming language, variables are used to store data values.

JavaScript uses the var keyword to define variables.

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:

var x;

x = 6;

 JavaScript Operators

JavaScript uses an assignment operator ( = ) to assign values to variables:

var x = 5;
var y = 6;

JavaScript uses arithmetic operators ( + - *  / ) to compute values:

(5 + 6) * 10

JavaScript Comments

Not all JavaScript statements are "executed".

Code after double slashes // or between /* and */ is treated as a comment.

Comments are ignored, and will not be executed:

var x = 5;   // I will be executed

// var x = 6;   I will NOT be executed

JavaScript is Case Sensitive

All JavaScript identifiers are case sensitive. 

The variables lastName and lastname, are two different variables.

lastName = "Doe";
lastname = "Peterson";

JavaScript does not interpret VAR or Var as the keyword var.

It is common, in JavaScript, to use camelCase names. You will often see names written like lastName (instead of lastname).

JavaScript Arithmetic Operators

Arithmetic operators are used to perform arithmetic between variables and/or values.

Operator	Description
+	Addition
-	Subtraction
*	Multiplication
/	Division
%	Modulus
++	Increment
--	Decrement

JavaScript Assignment Operators

Assignment operators are used to assign values to JavaScript variables.

Operator	Example	Same As
=	x = y	x = y
+=	x += y	x = x + y
-=	x -= y	x = x - y
*=	x *= y	x = x * y
/=	x /= y	x = x / y
%=	x %= y	x = x % y

The = assignment operator assigns a value to a variable.

Adding Strings and Numbers

Adding two numbers, will return the sum, but adding a number and a string will return a string:

Example

x = 5 + 5;
y = "5" + 5;
z= "Hello" + 5;

The result of x, y, and z will be:

10
55
Hello5

JavaScript Data Types

JavaScript variables can hold many data types: numbers, strings, arrays, objects and more:

var length = 16;                               // Number
var lastName = "Johnson";                      // String
var cars = ["Saab", "Volvo", "BMW"];           // Array
var x = {firstName:"John", lastName:"Doe"};    // Object

The Concept of Data Types

In programming, data types is an important concept.

To be able to operate on variables, it is important to know something about the type.

Without data types, a computer cannot safely solve this:

var x = 16 + "Volvo";

Does it make any sense to add "Volvo" to sixteen? Will produce a result? Will it produce an error?

JavaScript will treat the example above as:

JavaScript:

var x = "16" + "Volvo";

If the second operand is a string, JavaScript will also treat the first operand as a string.

Example:

var x = 16 + "Volvo";

JavaScript evaluates expressions from left to right. Different sequences can produce different results:

var x = 16 + 4 + "Volvo";

Result:

20Volvo

JavaScript:

var x = "Volvo" + 16 + 4;

Result:

Volvo164

In the first example, JavaScript treats 16 and 4 as numbers, until it reaches "Volvo".
In the second example, since the first operand is a string, all operands are treated as strings.

JavaScript Has Dynamic Types

JavaScript has dynamic types. This means that the same variable can be used as different types:

Example

var x;               // Now x is undefined
var x = 5;           // Now x is a Number
var x = "John";      // Now x is a String

JavaScript Strings

A string (or a text string) is a series of characters like "John Doe".

Strings are written with quotes. You can use single or double quotes:

Example

var carName = "Volvo XC60";   // Using double quotes
var carName = 'Volvo XC60';   // Using single quotes

You can use quotes inside a string, as long as they don't match the quotes surrounding the string:

Example

var answer = "It's alright";             // Single quote inside double quotes
var answer = "He is called 'Johnny'";    // Single quotes inside double quotes
var answer = 'He is called "Johnny"';    // Double quotes inside single quotes

You will learn more about strings later in this tutorial.

JavaScript Numbers

JavaScript has only one type of numbers.

Numbers can be written with, or without decimals:

Example

var x1 = 34.00;     // Written with decimals
var x2 = 34;        // Written without decimals

Extra large or extra small numbers can be written with scientific (exponential) notation:

Example

var y = 123e5;      // 12300000
var z = 123e-5;     // 0.00123

You will learn more about numbers later in this tutorial.

JavaScript Booleans

Booleans can only have two values: true or false.

Example

var x = true;
var y = false;

Booleans are often used in conditional testing.

You will learn more about conditional testing later in this tutorial.

JavaScript Arrays

JavaScript arrays are written with square brackets.

Array items are separated by commas.

The following code declares (creates) an array called cars, containing three items (car names):

Example

var cars = ["Saab", "Volvo", "BMW"];

Array indexes are zero-based, which means the first item is [0], second is [1], and so on.

You will learn more about arrays later in this tutorial.

JavaScript Objects

JavaScript objects are written with curly braces.

Object properties are written as name:value pairs, separated by commas.

Example

var person = {firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"};

The object (person) in the example above has 4 properties: firstName, lastName, age, and eyeColor.

You will learn more about objects later in this tutorial.

The typeof Operator (like calculator input check and validate)

You can use the JavaScript typeof operator to find the type of a JavaScript variable:

Example

typeof "John"                // Returns string
typeof 3.14                  // Returns number
typeof false                 // Returns boolean
typeof [1,2,3,4]             // Returns object
typeof {name:'John', age:34} // Returns object

 

In JavaScript, an array is a special type of object. Therefore typeof [1,2,3,4] returns object.

Undefined

In JavaScript, a variable without a value, has the value undefined. The typeof is also undefined.

Example

var person;                  // The value is undefined, the typeof is undefined

You will learn more about undefined later in this tutorial.

Empty Values

An empty value has nothing to do with undefined.

An empty string variable has both a value and a type.

Example

var car = "";                // The value is "", the typeof is string

JavaScript Functions

A JavaScript function is a block of code designed to perform a particular task.

A JavaScript function is executed when "something" invokes it (calls it).

Example

function myFunction(p1, p2) {
    return p1 * p2;              // The function returns the product of p1 and p2
}

JavaScript Function Syntax

A JavaScript function is defined with the function keyword, followed by a name, followed by parentheses ().
Function names can contain letters, digits, underscores, and dollar signs (same rules as variables).
The parentheses may include parameter names separated by commas: (parameter1, parameter2, ...)
The code to be executed, by the function, is placed inside curly brackets: {}

function functionName(parameter1, parameter2, parameter3) {
    code to be executed
}

Function parameters are the names listed in the function definition.
Function arguments are the real values received by the function when it is invoked.
Inside the function, the arguments are used as local variables.

A Function is much the same as a Procedure or a Subroutine, in other programming languages.

Function Invocation

The code inside the function will execute when "something" invokes (calls) the function:

• When an event occurs (when a user clicks a button)
• When it is invoked (called) from JavaScript code
• Automatically (self invoked)

You will learn a lot more about function invocation later in this tutorial.

Function Return

When JavaScript reaches a return statement, the function will stop executing.
If the function was invoked from a statement, JavaScript will "return" to execute the code after the invoking statement.
Functions often compute a return value. The return value is "returned" back to the "caller":

Example

Calculate the product of two numbers, and return the result:

var x = myFunction(4, 3);        // Function is called, return value will end up in x

function myFunction(a, b) {
    return a * b;                // Function returns the product of a and b
}

The result in x will be:

12

Why Functions?

You can reuse code: Define the code once, and use it many times.
You can use the same code many times with different arguments, to produce different results.