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0.2 — Introduction to programming languages

Modern computers are incredibly fast, and getting faster all the time. Yet with this speed comes some significant constraints: Computers only natively understand a very limited set of commands, and must be told exactly what to do.

A computer program (also commonly called an application) is a set of instructions that the computer can perform in order to perform some task. The process of creating a program is called programming. Programmers typically create programs by producing source code (commonly shortened to code), which is a list of commands typed into one or more text files.

The collection of physical computer parts that make up a computer and execute programs is called the hardware. When a computer program is loaded into memory and the hardware sequentially executes each instruction, this is called running or executing the program.

Machine Language

A computer’s CPU is incapable of speaking C++. The limited set of instructions that a CPU can understand directly is called machine code (or machine language or an instruction set).

Here is a sample machine language instruction: 10110000 01100001

Back when computers were first invented, programmers had to write programs directly in machine language, which was a very difficult and time consuming thing to do.

How these instructions are organized is beyond the scope of this introduction, but it is interesting to note two things. First, each instruction is composed of a sequence of 1’s and 0’s. Each individual 0 or 1 is called a binary digit, or bit for short. The number of bits that make up a single command vary -- For example, some CPUs process instructions that are always 32 bits long, whereas some other CPUs (such as the x86 family, which you are likely using) have instructions that can be a variable length.

Second, each set of binary digits is interpreted by the CPU into a command to do a very specific job, such as compare these two numbers, or put this number in that memory location. However, because different CPUs have different instruction sets, instructions that were written for one CPU type could not be used on a CPU that didn’t share the same instruction set. This meant programs generally weren’t portable (usable without major rework) to different types of system, and had to be written all over again.

Assembly Language

Because machine language is so hard for humans to read and understand, assembly language was invented. In an assembly language, each instruction is identified by a short abbreviation (rather than a set of bits), and names and other numbers can be used.

Here is the same instruction as above in assembly language: mov al, 061h

This makes assembly much easier to read and write than machine language. However, the CPU can not understand assembly language directly. Instead, the assembly program must be translated into machine language before it can be executed by the computer. This is done by using a program called an assembler. Programs written in assembly languages tend to be very fast, and assembly is still used today when speed is critical.

However, assembly still has some downsides. First, assembly languages still require a lot of instructions to do even simple tasks. While the individual instructions themselves are somewhat human readable, understanding what an entire program is doing can be challenging (it’s a bit like trying to understand a sentence by looking at each letter individually). Second, assembly language still isn’t very portable -- a program written in assembly for one CPU will likely not work on hardware that uses a different instruction set, and would have to be rewritten or extensively modified.

High-level Languages

To address the readability and portability concerns, new programming languages such as C, C++, Pascal (and later, languages such as Java, Javascript, and Perl) were developed. These languages are called high level languages, as they are designed to allow the programmer to write programs without having to be as concerned about what kind of computer the program will be run on.

Here is the same instruction as above in C/C++: a = 97;

Much like assembly programs, programs written in high level languages must be translated into a format the computer can understand before they can be run. There are two primary ways this is done: compiling and interpreting.

A compiler is a program that reads source code and produces a stand-alone executable program that can then be run. Once your code has been turned into an executable, you do not need the compiler to run the program. In the beginning, compilers were primitive and produced slow, unoptimized code. However, over the years, compilers have become very good at producing fast, optimized code, and in some cases can do a better job than humans can in assembly language!

Here is a simplified representation of the compiling process:

Example of compiling

Since C++ programs are generally compiled, we’ll explore compilers in more detail shortly.

An interpreter is a program that directly executes the instructions in the source code without requiring them to be compiled into an executable first. Interpreters tend to be more flexible than compilers, but are less efficient when running programs because the interpreting process needs to be done every time the program is run. This means the interpreter is needed every time the program is run.

Here is a simplified representation of the interpretation process:

Example of interpreting

Optional reading

A good comparison of the advantages of compilers vs interpreters can be found here

Most languages can be compiled or interpreted, however, traditionally languages like C, C++, and Pascal are compiled, whereas “scripting” languages like Perl and Javascript tend to be interpreted. Some languages, like Java, use a mix of the two.

High level languages have many desirable properties.

First, high level languages are much easier to read and write because the commands are closer to natural language that we use every day. Second, high level languages require fewer instructions to perform the same task as lower level languages, making programs more concise and easier to understand. In C++ you can do something like a = b * 2 + 5; in one line. In assembly language, this would take 5 or 6 different instructions.

Third, programs can be compiled (or interpreted) for many different systems, and you don’t have to change the program to run on different CPUs (you just recompile for that CPU). As an example:

Example of portability

There are two general exceptions to portability. The first is that many operating systems, such as Microsoft Windows, contain platform-specific functions that you can use in your code. These can make it much easier to write a program for a specific operating system, but at the expense of portability. In these tutorials, we will avoid any platform specific code.

Some compilers also support compiler-specific extensions -- if you use these, your programs won’t be able to be compiled by other compilers that don’t support the same extensions without modification. We’ll talk more about these later, once you’ve installed a compiler.

Rules, Best practices, and warnings

As we proceed through these tutorials, we’ll highlight many important points under the following three categories:

Rule

Rules are instructions that you must do, as required by the language. Failure to abide by a rule will generally result in your program not working.

Best practice

Best practices are things that you should do, because that way of doing things is generally considered a standard or highly recommended. That is, either everybody does it that way (and if you do otherwise, you’ll be doing something people don’t expect), or it is superior to the alternatives.

Warning

Warnings are things that you should not do, because they will generally lead to unexpected results.


0.3 -- Introduction to C/C++
Index
0.1 -- Introduction to these tutorials

205 comments to 0.2 — Introduction to programming languages

  • Roly Glez

    Hey, I'm using this to review Cpp from my computer engineering bachelors. Thanks for this guide!

  • Kyaw Zin Thet

    Hi Sir Alex,

    I just want to say thank you so much for your effort and time to support all of us.
    I really like your explanation and tutorials.

  • Rick

    Hello Alex, I'm a Jamaican and is trying to be a self taught programmer until i can afford to attend an institution. As far as i can see this tutorial is great so far, I've tried video tutorial but got to a point and stopped. So what i want to say is great job and keep it up.
    ps. Can i get your email address.

  • Jack Bing

    From what I gather, the compiler essentially creates code that is executable as per that systems CPU architecture. Also, platform specific functions in code can only be used on that particular platform, and the compiler and CPU architecture have only support of the platform to do with it. But suppose, two different computer architectures of CPU's could host the same platform, then would the two different compilers for the two different systems both allow for the functions ? Is it even possible for two architectures to host the same platform ? Correct me if I have got something fundamentally wrong.

    • Alex

      Linux is a good example of a platform that's been ported to different architectures (see https://en.wikipedia.org/wiki/List_of_Linux-supported_computer_architectures). Generally, executables only support the OS and architecture they were built for. You can read more here: https://en.wikipedia.org/wiki/Cross-platform

  • What do you mean. A = 97

    What interpetation would be applied?
    Is that equal to binary and assembly, examples on page.
    Where is the language generated?

  • Rafael A. A. Merlo

    Hey Alex =)

    Really, thank you very much for all the time, effort and love you put in providing all this great educational material for free for us. You are awsome!

    Me and a friend have decided yesterday to follow your material from zero to end. My personal goal for this is to take a Open Source music notation software, MuseScore (which is written in C++ and Qt), and write a big scope plugin for it that transforms and add to it a interface to write dance notation.

    Probably I'll need to find another site to learn the Qt programming language, but for the little I unterstood from it seems it was build over the C++, am I right?

    Well, wish us luck :D
    Hugs from Brazil o/

    • Alex

      Yep. Qt has a few extra things you'll want to learn about (e.g. how the slots and signals system works, and how to instantiate windows), but once you know the basics of C++ this should all be doable.

  • Duy

    I just find out this website, I think it is great to learn c++.

  • James

    I just found this site today, I'm really excited to begin learning one of the most popular and useful high-level programming languages out there today.  Although I'm nearly 33 years old, it's not too late to get into such an amazing and profitable new skillset.  Good luck to everyone on their own adventure.

  • ayush singh

    which programming language is best for begginers other than c++ if i am a school grade student

  • Am I correct to think that the assembly instruction (for reference, this was

    ) instructs the processor to "move into the al register the hexadecimal value 061"? I mean I might as well learn a little "bit" (pardon  the pun) of x86 assembly while I'm here :-)

  • Elton Ngugi

    this is the best site to learn any programing language.The explanation is very detailed and leaves one with complete understanding. I highly recommend everyone to visit and use this site for individual benefits.
    Thank you

  • Denise

    Great tutorial..!

  • Isabel

    Hi Alex! Thank you for sharing your knowledge! you have my respect! I think I'm kind of confused with some information. I don't think I have very clear the difference between an assembler and a compiler, and the other things I cannot figure them out, are these three concepts: x86 compiler, PowerPC, MIPS. Finally, another concept that I don't completely understand, is the computer architecture. Thank you Alex you awesome!

    • Alex

      And assembler is used for compiling assembly code into an executable that can be run. A compiler is used for compiling a high-level language into an executable that can be run.
      x86, PowerPC, and MIPS are all different computer architectures. They have different instruction sets, different strengths and weaknesses, and different assembly language. But they can all compile the same C/C++ code.
      For more info on computer architectures, see https://en.wikipedia.org/wiki/Computer_architecture

  • Hi Alex,

    Your tutorials are really very helpful to learn C++ easily. I've already started to learn and have determined to finish it. Why I would be failed to cover the whole ready made amazing lessons while the master of C++ (Alex) have already been covered up all the lessons with good explanation for learning?

    Thanks a lot sir.

  • Ganesh Bhadane

    Hi Alex,
    I have simple question. What is compile time and runtime??

  • nida

    I have no knowledge about any basics to programming. Can i complete this course?

  • Abhishek Raina

    Hello teacher,
    First of all thank you for posting this and helping all of us!
    So I have been learning java (on blueJ) for a few years and it will continue for a few more years. My problem is will learning C++ make it difficult for me to understand java? I was scrolling down the index of learncpp and most of the topics looked familiar. Is C++ similar to java or is it very different? I really wanted to learn C++ but I could not let it hinder my progress in java.
    What do you suggest?
    Thanks!

  • Xrem

    The material in this site is so clear and straight-forward. I will try to click every add on the pages. Thank you sooooooooo much.

  • Therese McLeod

    #include <iostream>
    using namespace std;
    void doPrint()
    {
        cout << "In doPrint()" << endl;
    }

    int main()
    {
        cout << "Starting Main()" << endl;
        doPrint();
        cout << "Ending Main()" << endl;
        return 0;
    }
    Yay, it was broken, now it's fixed, the solution was strange, languages betwixt.
    Therese

  • disha

    Hi Alex,

    Thanx aloooooott for such a beautiful website.. no words to explain how useful it is..

    I've a que that:

    I've done my bachelors degree in computers..

    if I'm learning c++ from here in a best way then of course there is no need for a classes but I wanna get certified in c++ then how will i get a certification for the same???

    I need a certification which is acceptable for all the well known companies..

    Is there any way that we can directly apply for a certification and get it.. if yes then where and how can we apply and how much expenses will it take??

    do rply plzz.. it's really very important for me...

    and thanks in advance..

    • Alex

      There are a few companies that offer certifications in C++. Microsoft is probably the best known of the bunch. However, certifications don't tend to be very highly regarded in programming, so I'm not sure that's a worthwhile course of action.

  • Ben

    In what way can I support this noble effort, Alex? I am studying Cloud Computing and knowledge of C++ is required.

  • Lizzy

    Does learncpp have any connection to codecademy? Because this comment is using my codecademy profile pic.

    • Alex

      This site has no association with codeacademy. However, if you comment and use an email address that has an associated gravatar, we'll pull it in the gravatar and display it. Look up gravatar for more information on what it is.

  • GEScott71

    This sounds great so far - thanks for the great intro.  I am going to work through this entire tutorial, and will comment after each section as to how I am doing (and likely with many questions!).

    I found many of the comments above motivating, so I'll add a few details about myself and motivation here.

    I am a 45yo product manager of embedded systems for railroad locomotives, working for General Electric.  I am a mechanical engineer by education.  I haven't done any programming since BASIC in junior high and 1 semester of FORTRAN in college.  I want to learn to code for 2 reasons:  1)GE is working to become a software company and I want to better understand how software is created and implemented to do my job better, and 2)There are some small personal projects I want to develop my own programs for, as I haven't found pre-built solutions.

    Thanks Alex!

  • Clark

    Great site, I'm so happy that I found it, keep up the good work, cheers mate !

  • dontletmegetme

    I love this website

  • UKImperium

    Easy to read & learn. It's great, not like most sites you visit where they bored you on the first sentence.

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