Web Programming and Problem Solving презентация

Usually, JavaScript is used in web pages… for now, we will just concentrate on basics of the language
A JavaScript Interpreter:
http://www.webtoolkitonline.com/javascript-tester.html
Getting Started with JavaScript

Try the following program:
A First Program
var a;
var b;
var c;
a = 13;
b = 200;
c = a + b;
document.write(c);

var a;
var b;
var c;
a = 13;
b = 200;
c = a + b;
document.write(c);
In programs, variables are labels that represent places where data is stored
The data that is stored inside a variable is called its value
Values and Variables
What are the variables and their values in this program?

To tell the computer to set aside storage space for a variable, you should declare the variable
Declaration
In JavaScript, you declare variables using the var keyword
var a;
var b;
var c;
a = 13;
b = 200;
c = a + b;
document.write(c);

To change the value stored in a variable, you assign it a new value using the equals sign
Assignment
Examples of assignments
var a;
var b;
var c;
a = 13;
b = 200;
c = a + b;
document.write(c);

Expressions are things that can have a value
Expressions
Examples:
Variables
Numbers and other literals
Expressions joined together by operators (e.g., +, -, *, /)
var a;
var b;
var c;
a = 13;
b = 200;
c = a + b;
document.write(c);
What expressions do you see in this program?

Statements are the elements in code that perform individual tasks in sequential order
Think “a line of code”
Often end with a semicolon
Examples:
Declarations
Assignments
Function calls
Statements
var a;
var b;
var c;
a = 13;
b = 200;
c = a + b;
document.write(c);
What are the statements in this program?

Arithmetic operations (+, -, *, /) can be used
Order of operations: * and / take precedence over + and –
Exercise: What values do these produce?
100 + 4 * 11
(100 + 4) * 11
115 * 4 – 88 / 2
Working with Numbers

Add code to the following program to convert Fahrenheit to Celsius using the formula:
(F – 32) * 5/9 = C
Exercise 1
var fahr = 100;
var cels;
// add your code here
document.write(cels);

Add code to the following program to calculate the average of a, b, and c
Exercise 2
var a = 10;
var b = 20;
var c = 25;
var avg;
// add your code here
document.write(avg);