Programming Languages (High-Level Languages)

Almost all of the computer programming these days is done with high-level programming languages.  There are lots of them and some are quite old.  COBOL, FORTRAN, and Lisp were devised in the 1950s!!!  As you will see, high-level languages make it easier to describe the pieces of the program you are creating.  They help by letting you concentrate on what you are trying to do rather than on how you represent it in a specific computer architecture.  They abstract away the specifics of the microprocessor in your computer.  And, all high-level languages come with large sets of common stuff you need to do, called libraries.
In this introduction, you will work with two computer programming languages: Logo and Java.  Logo comes from Bolt, Beranek & Newman (BBN) and Massachusetts Institute of Technology (MIT).  Seymour Papert, a scientist at MIT's Artificial Intelligence Laboratory, and co-workers championed this computer programming language in the 70s.  More research of its use in educational settings exists than for any other programming language.  In fact, the fairly new Scratch Programming Environment (also from MIT) consists of a modern graphical user interface on top of Logo-like functionality.
Java is a fairly recent programming language.  It appeared in 1995 just as the Internet was starting to get lots of attention.  Java was invented by James Gosling, working at Sun Microsystems.  It's sort-of a medium-level language.  One of the big advantages of learning Java is that there is a lot of software already written ( see: Java Class Library) which will help you write graphical programs that run on the Internet.  You get to take advantage of software that thousands of programmers have already written.  Java is used in a variety of applications, from mobile phones to massive Internet data manipulation.  You get to work with window objects, Internet connection objects, database access objects and thousands of others.  Java is the language used to write Android apps.
So, why do these lessons start with the Logo programming language?  No other language has the depth of research devoted to its use in educational settings.  Hundreds of books and research papers have been written regarding its use in the classroom.  Cynthia Solomon, who started MIT's Logo Group with Dr. Papert, has put together a comprehensive website on Logo: logothings.wikispaces.com.
I like using the Logo language to teach introductory programming because it is very easy to learn.  The faster you get to write interesting computer programs the more fun you will have.  And... having fun is important!  But do not let Logo's simplicity fool you into thinking it is just a toy programming language.  Logo is a derivative of the Lisp programming language, a very powerful language still used today to tackle some of the most advanced research being performed.  Brian Harvey shows the power of Logo in his Computer Science Logo Style series of books.  Volume 3: Beyond Programming covers six college-level computer science topics with Logo.
Both Logo and Java have the same sort of stuff needed to write computer programs. . They have the ability to manipulate objects including lots of arithmetic functions, you can compare objects and do different things depending on the outcome of the comparison, and they provide ways to control the order in which instructions get performed.  And... that's what programming is really all about... as you will see.
Just to give you a feel for what programming is like in a high-level language, here's a program that greets us, pretending to know English.

    print [Hello world!]
   

This is one of the simplest programs that can be written in most high-level languages.  PRINT is a command in Logo  When it is performed, it takes whatever follows it and displays it.  The "Hello world" program is famous; checkout its description on Wikipedia by clicking here.
In addition to commands, Logo has operators that output some sort of result.   Although it's a bit contrived, here is a program that displays the product of a constant number (ten) and a random number in the range of zero through fourteen.

    print product 10 (random 15)
   

In this source code, the PRINT command's input is the output of the PRODUCT operator.  PRODUCT multiplies whatever follows it by whatever follows that and outputs the result.  So, PRODUCT needs two inputs.  RANDOM is an operator that outputs a number that is greater than or equal to zero (0) and less than the number following it.  So, PRODUCT gets its second input from the output of RANDOM. Confusing?  Figure 1.1 shows a plumbing diagram, how all these procedures fit together.  Still confusing?  Don't worry, we will get into the details of Logo operators in lesson 8.
Figure 1.1 Finally, here's an snipet of advanced Logo source code, just to give you a feeling for what it looks like.  This is a procedure definition for selecting the maximum number from a list of numbers.

    to getMax :maxNum :numList 
      if empty? :numList [output :maxNum]
      if greater? (first :numList) :maxNum [output getMax (first :numList) (butfirst :numList)]
      output getMax :maxNum (butfirst :numList)
      end 
   

Again, do not worry if you do not understand exactly what this procedure does.  It will be a while before you will be writing anything like this.  But, I want you to see that the words that make up the program's instructions and the instructions themselves are similar to English sentences, e.g., the first line and a half in the procedure are similar to the sentences:

    If the list of numbers to process is empty then output the maximum number processed.
    If the first number in the list is greater than the maximum number processed so far then ...
   

So, a high-level programming language is *sort-of* like English, just one step closer to what the language a computer really understands looks like.  Now let's move on to what a computer's native language looks like when it is given a symbolic representation.

Programming Using the English Language

Remember what I said in the Introduction to this lesson?

   
      Writing software, computer programs, is a lot like
      writing down the steps it takes to do something. 
         

Before we see what a computer programming language looks like, let's use the English language to describe how to do something as a series of steps.  A common exercise that really gets you thinking about what computer programming can be like is to describe a process you are familiar with.

      Describe how to make a peanut butter and jelly sandwich.
   

Rather than write my own version of this exercise, I searched the Internet for the words "computer programming sandwich" using Google.  One of the hits returned was http://teachers.net/lessons/posts/2166.html.  At the link, Deb Sweeney (Tamaqua Area Middle School, Tamaqua, PA) described the problem as:

      Objective: Students will write specific and sequential steps
   on how to make a peanut butter and jelly sandwich.

      Procedure: Students will write a very detailed and step-by-step
   paragraph on how to make a peanut butter and jelly
   sandwich for homework. The next day, the students will
   then input (read) their instructions to the computer
   (teacher). The teacher will then "make" the programs,
   being sure to do exactly what the students said...
   

When this exercise is directed by an experienced teacher or mentor it is excellent for demonstrating how careful you need to be, how detailed you need to be, when writing a computer program.  
Programming in a natural language, say the full scope of the English language, seems like a very difficult task.  But, before moving on to languages we can write programs in today, I want to leave on a high note.