Introduction to
Computer Programming

Matt Wilber

@greenzeta

greenzeta.com

What is a computer?

  • A computer is a machine that follows instructions.
     
  • Programming is writing the instructions for the computer to follow.

10 PRINT "HELLO"

20 GOTO 10

What is programming?

  • The computer understands ones and zeros (binary). This is called “machine language”.
     
  • It’s possible to write machine language, but it’s very difficult. Instead, we write in a “programming language” that’s easy to read.
     
  • The programming language is converted into machine language by a program called a “compiler”.
     
  • There are tons of programming languages. Some have specific purposes: Organizing information (HTML), Design (CSS) or Interaction (JavaScript)

 

Example Machine Language

What is JavaScript?

  • A programming language created to make web pages interactive.
     
  • It uses a special type of compiler called an  “interpreter”.
     
  • Normally, you have to wait for a compiler. But an interpreter runs your program instructions as it converts them.
     
  • All modern web browsers have JavaScript interpreters.

 

Let's Write a Program!

  • Every JavaScript environment has a “console”.  It's your behind-the-scenes interface.
     
  • You can open the console in Chrome by pressing F12.
     
  • You can type JavaScript instructions directly into the console and the interpreter will run them.
     
  • Let's write our first instruction:

 

console.log('This is my message');

Programming Concept: Variables

  • Computer memory is broken up into a grid of empty spaces. Each space has a number called an “address”.
     
  • Remembering numbers is hard. So programming languages allow us to give the memory space a name.
     
  • The spaces we give names are called “variables”. They’re called that because the stuff in the computer memory can vary.

Creating Variables

  • To create a variable, you write an instruction to “declare” it. Part of this instruction is the name you want to call it.
     
  • The instruction to declare a variable is “var”


     
  • Once you declare a variable, you can store or “assign” information to it. You assign information to a variable by writing an instruction that sets it equal to the value you want to store.


     
  • The above instruction tells the computer to locate the memory space we named myAwesomeVariable, and put the number 42 in it.
var myAwesomeVariable;
myAwesomeVariable = 42;

JavaScript Variable Types

  • Variables can hold different “types” of information:
    • number
       
       
    • string (text)

       
    • boolean (true or false)

       
    • object (groups of variables)

       
    • null (empties the memory space)
var myAwesomeVariable = 42;
var myAwesomeVariable = 'Some text I wrote.';
var myAwesomeVariable = true;
var myAwesomeVariable = {name: 'Matt'};
var myAwesomeVariable = null;

Let's Write a Program!

  • ​First declare a variable.
     
  • Then assign something to that variable.
     
  • Then use the console to display the contents of that variable.

 

var myAwesomeVariable;
myAwesomeVariable = 'Awesomeness!!!';
console.log(myAwesomeVariable);

Let's Write a Program!

  • ​First declare a variable.
     
  • Then assign something to that variable.
     
  • Then use the console to display the contents of that variable.

 

Programming Concept: Operators

  • Computers store data, and they can change that stored data.
     
  • One of the ways we tell the computer how to change data is with a program instruction called an “operator.”
     
  • One example of an operator is “addition” which is written as +
     
  • The addition operator tells the computer to add numbers: 2 + 2

Types of Operators

  • There are lots of different operators. In fact, you already used one. That equal sign used to put a value in a variable is an "assignment operator".
     
  • "Arithmetic operators" perform mathematical functions:
    •  +  Addition
    •  -   Subtraction
    •  *  Multiplication
    •  /   Division
       
  • Sometimes an operator works differently depending on the data type. You can use the addition operator on two strings to join them together. This is called "string concatenation"
    • "Hello" + "World" = "HelloWorld"

Using Operators to Change Data

  • When you create a variable you write an instruction to assign a value to it. You can include other operators in that instruction to perform  multiple operations at the same time:

     
  • The above instruction first adds the numbers and then assigns the result to the variable. myVariable contains 42.
     
  • You can even perform an operation on the value of a variable and then assign the result back to itself.


     
  • The above instructions produce the same result as the first one.
myVariable = 40 + 2;
myVariable = 40;
myVariable = myVariable + 2;

Let's Write a Program!

  • ​First declare a variable and assign a number to it.
     
  • Use the assignment and multiplication operators to double the number in the variable.
     
  • Then use the console to display the contents of that variable.

 

Let's Write a Program!

  • ​First declare a variable and assign a number to it.
     
  • Use the assignment and multiplication operators to double the number in the variable.
     
  • Then use the console to display the contents of that variable.

 

var myNumber;
myNumber = 21;
myNumber = myNumber * 2;
console.log(myNumber);

Programming Concept: Comparison Operators

  • Logic deals in absolutes, either something is true, or it's false. We tell the computer how to respond in this way by using a “comparison operator”.
     
  • A comparison operator creates a condition, then produces a boolean value of "true" if the condition is met or "false" if it's not met.
     
  • One comparison operator is called “equality” and is written as ==. It's like saying “is equal to”. You can tell the computer how to understand when something is equal to the number 42 by writing an instruction like this:

     
  • When the variable someNumber contains the value 42, the comparison operator produces a value of true. When someNumber contains anything other than 42, it produces false.
someNumber == 42

Common Comparison Operators

  • There are other comparison operators. Here are a few to get started. We'll cover more later:
    • is equal to
       
       
    • is not equal to

       
    • is greater than

       
    • is less than
       
  • All of the example comparisons above will produce a value of true
42 == 42
33 != 42
66 > 42
33 < 42

Programming Concept: Conditionals

  • Computers don’t really think, but they can make decisions...
     
  • We tell the computer how to decide by writing an instruction called a “conditional statement”.
     
  • We're able to make computers appear smart, by writing lots of conditional statements.
     
  • Conditionals are written in the form of:
    If something is true then do this.

Writing a Conditional Statement

  • Let's use a comparison operator to complete a conditional statement.


     

  • The instruction above tells the computer to do something when the contents of the variable “someNumber” is equal to 42.
     
  • The brackets wrap a set of instructions we want the computer to follow when the result of the logical operation is true.
     
  • If the variable someNumber is anything other than 42, the computer skips the instructions inside the brackets.
if( someNumber == 42 ){
  // do something
}

A line that begins with // is called a “comment.” Comments are notes for humans to read and are ignored by the computer.

Let's Write a Program!

  • ​Declare a variable and assign your name to it.
     
  • Add a conditional statement where the program writes "I know you." to the console only if the variable contains your name.
     
  • Add a second conditional statement that writes "I do not know you." to the console if the variable does not contain your name.
     
  • Run the program. Then assign a different name to the variable and run it again

 

var myName = 'Matt';
if( myName == 'Matt' ){
  console.log('I know you.');
}
if( myName != 'Matt' ){
  console.log('I do not know you.');
}

Let's Write a Program!

  • ​Declare a variable and assign your name to it.
     
  • Add a conditional statement where the program writes "I know you." to the console only if the variable contains your name.
     
  • Add a second conditional statement that writes "I do not know you." to the console if the variable does not contain your name.
     
  • Run the program. Then assign a different name to the variable and run it again

 

Conditionals Continued: Else / Else If

  • Often, you want the computer to do something different if your condition is not true.
     
  •  It's perfectly fine to write two separate conditionals.





     
  • Since the second condition is only true when the
    first is false, we can consolidate the two using "else".
if( myName == 'Matt' ){
  console.log('I know you.');
}
if( myName != 'Matt' ){
  console.log('I do not know you.');
}
if( myName == 'Matt' ){
  console.log('I know you.');
}else{
  console.log('I do not know you.');
}

Programming Concept: Logical Operators

  • Sometimes you need compare more than one piece of data. You can string together comparisons into more complex conditions using "logical operators".
     
  • There are three logical operators in JavaScript: "AND", "OR", "NOT".
     
  • Consider the variables firstName = 'Matt' and lastName = 'Wilber':
     
  • AND   &&   : True when both comparisons are true

     
  • OR      ||    : True when at least one comparison is true

     
  • NOT     !      : True when a comparison is false

     
  • All of the above conditions return a value of true.
!(lastName == 'Smith')
(firstName == 'John') || (lastName == 'Wilber')
(firstName == 'Matt') && (lastName == 'Wilber')

Let's Write a Program!

  • ​Declare two variables: firstName, lastName and set them equal to your name.
     
  • Write a condition that says "Hello" only when firstName AND lastName are yours.
     
  • Write a condition that responds "Have we met before?" when lastName is yours OR firstName is yours.
     
  • Write a condition that responds "I do not know you" when both firstName AND lastName are NOT yours.

 

Let's Write a Program!

var firstName = 'Matt';
var lastName = 'Wilber'
if( (firstName == 'Matt') && (lastName == 'Wilber')  ){
  console.log('I know you.');
}else if( (firstName == 'Matt') || (lastName == 'Wilber')  ){
  console.log('Have we met before?');
}else if(!(firstName == 'Matt') && !(lastName == 'Wilber')){
  console.log('I do not know you');
}

Programming Concept: Loops

  • One of the things computers do best is repeating tasks over and over again.  You can make a computer repeat things by writing an instruction called a "loop".
     

  • The instructions that are repeated in the loop must eventually change a condition to false. The false condition will end or "break" the loop.
     

  • If the loop is never broken, it will repeat forever until you turn off your computer. Or, in the case of JavaScript, close your browser. A never ending loop is called an "infinite loop". It's important to avoid infinite loops in your programs.
  • One type of loop is called a "while loop".  Like a conditional statement, a while loop executes a group of instructions if a condition is met. The loop will repeat those instructions over and over until the condition is not met.

while( [logical operation is true] ){
  // instructions to repeat
}

The While Loop

Let's Write a Program!

  • ​Declare a variable named "counter". Set it equal to 0.
     
  • Write a loop command that will repeat while counter is less than 10.
     
  • On each iteration of the loop, add 1 to counter.

Let's Write a Program!

  • ​Declare a variable named "counter". Set it equal to 0.
     
  • Write a loop command that will repeat while counter is less than 10.
     
  • On each iteration of the loop, add 1 to counter.
var counter = 0;
while( counter < 10 ){
  console.log('The counter is ' + counter);
  counter = counter + 1;
}

Programming Concept: Arrays

  • Computers often work with long lists of data. You can store these lists in a special kind of variable called an "array".
     
  • Each item in an array is numbered in the order it is added. This number is called its "index".
     
  • You access the data in the array by writing its variable name, followed by the number of the item.
     
  • You must add items to an array in order, but you can access them in any order you need.

Working with Arrays

  • You use brackets to define an array and commas to separate its items


  • The instruction above creates 3 data containers and stores them under the single variable name myArray.

  • You can access each data container like any other variable. In the case of an array, you have to specify the number of the item starting with 0.


  • The instruction above returns the data of the first item in the array, which is 'a'.
var myArray = [ 'a', 'b', 'c' ];
myArray[0]

Let's Write a Program!

  • ​Declare an array of single letter strings that spell "javascript".
     
  • Declare another variable to count the length of the word.
     
  • Write a loop command that will repeat while counter is less than the length of the array.
     
  • On each iteration of the loop, use the counter variable to write the corresponding array element to the console. Afterward, add 1 to the counter.

Let's Write a Program!

  • ​Declare an array of single letter strings that spell "javascript".
  • Declare another variable to count the length of the word.
  • Write a loop command that will repeat while counter is less than the length of the array.
  • On each iteration of the loop, use the counter variable to write the corresponding array element to the console. Afterward, add 1 to the counter.
var counter = 0;
var letters = ['j', 'a', 'v', 'a', 's', 'c', 'r', 'i', 'p', 't'];
while( counter < letters.length ){
  console.log(letters[counter]);
  counter = counter + 1;
}

Programming Concept: Function

  • A "function" lets you wrap a bunch of instructions into a package that can be reused over and over again.
     
  • You assign a function a name, and then write a set of instructions for the function to use.
     
  • When you use a function, you can send it data. The data you send is called a "parameter". Parameters are like variables that the instructions in the function can use.
     
  • A function can output data as well. This is called a "return value"

Writing a Function

  • The instruction to create a function is... function. Just like a variable, you give a function a name:

     
  • The function name is always followed my parenthesis. There's a special reason for this that we'll get into next.
     
  • Finally, you add brackets to wrap the function's instructions.
     
  • Let's write a function called SaySomething that displays "HelloWorld" to the console.
function MyFunction()
function SaySomething(){
  console.log("HelloWorld");
}

Using a Function

  • Now that we've written a function, let's use it. You use a function by writing an instruction to "call" or "invoke" that function.
     
  • To call our SaySomething function, all we have to do is write its name, followed by the parenthesis.




     
  • I can call the function as many times as I want
function SaySomething(){
  console.log("HelloWorld");
}

SaySomething();
function SaySomething(){
  console.log("HelloWorld");
}

SaySomething();
SaySomething();
SaySomething();

Programming Concept: Parameters

  • A function that writes the same thing to the console every time isn't very useful. We can make the function perform different actions by "passing" a "parameter" to it.
     
  • Parameters are like variables, but they only exist to the instructions inside the function.
     
  • Let's modify the SaySomething function to accept a parameter which will be the string to display in the console. Just like variables, parameters have names too.



     
  • Now when I call the function, I can assign different data to the parameter each time.
function SaySomething(thingToSay){
  console.log(thingToSay);
}
function SaySomething(thingToSay){
  console.log(thingToSay);
}

SaySomething("Hello");
SaySomething("Hello Again");
SaySomething("Goodbye");

Let's Write a Program!

  • ​Declare a function called "add" that accepts two parameters.
     
  • Within the function, declare a variable "sum" and set it equal to the sum of the two parameters. Return sum.
     
  • Call the function and pass two numbers, write the total to the console.

Let's Write a Program!

  • ​Declare a function called "add" that accepts two parameters.
     
  • Within the function, declare a variable "sum" and set it equal to the sum of the two parameters. Return sum.
     
  • Call the function and pass two numbers, write the total to the console.
function add( addend1, addend2 ){
  var sum = addend1 + addend2;
  return sum;
}

var result = add( 3, 5 );
console.log('The sum of 3 and 5 is ' + result);

Programming Concept:

Object Oriented Programming (OOP)

  • You can group many variables and functions together into a single variable.
     
  • The group is called an "Object"
     
  • An object is a data type. Just like numbers, strings and booleans.
     
  • Objects allow you to organize and reuse your code.

Programming Concept: Class

  • A "Class" is a template for your Object. You write a class to define the variables and functions the object will contain.
     
  • An object variable is defined like any other variable. The computer assigns an object to the variable by creating a copy of the class in it. This copy is called an "instance" of the class.

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Introduction to Computer Programming

By Matthew Wilber

Introduction to Computer Programming

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