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  • Hi, my name is Alex and this is the first in a series of videos on becoming a better computer programmer.

  • For this particular video we're going to be focusing on the C programming language,

  • which is commonly used at universities as a teaching tool and has much in common with most languages used in commercial development.

  • At this point I am assuming zero knowledge of programming and C in general,

  • so obviously feel free to move to a more advanced video as your needs require.

  • By way of introduction, let me say I've been programming as a hobbyist and a professional for the best part of 13 years now,

  • having intially started with Basic before teaching myself C.

  • I now work for the market leader in financial analytics software,

  • still using the C family of languages on a day-to-day basis.

  • Whenever you encounter a new programming language you're invariably shown what's called a 'Hello World' program,

  • which is generally the simplest meaningful program that can be written in a language.

  • On screen now is the 'Hello World' program in C which we're going to pick apart over the next few minutes.

  • You can take this program and compile it in any C or C++ compiler,

  • such as Microsoft Visual Studio on Windows, which I'm using here.

  • The first thing to note about C is it's a procedural programming language.

  • This means the program is arranged as functions while control and execution flows from one function to another.

  • Your program is read and executed line-by-line by the computer.

  • You may be wondering how the computer knows where to start this execution,

  • and the answer is that when you compile your program it looks for a function named main, as this one is here.

  • It takes arguments, signified by the words in brackets, which are inputs from the command line

  • and returns an integer - signified by int. Don't worry if you don't understand these terms yet.

  • Note that you can have only one main function in a program or you won't be able to compile it.

  • Each function, including the main function, must be included in what's called a block, signified by these curly braces.

  • The code between these outer braces constitutes what's called the scope of the function.

  • This has implications later on when you declare variables

  • which only exist within the scope of a function, or a subsection of a function.

  • Again, don't worry about this too much now, and instead remember

  • that you can identify the scope of a block of code with these curly braces.

  • Functions also end in a return statement. If you're not returning anything specific

  • - that is, the function returns type void - you can skip the return statement altogether,

  • but it will just be implied by the compiler. When learning C,

  • you should use the return statement every time just to keep track of what you're doing in your program.

  • In this case, our function returns a 0; returning a zero from a main function of a program signifies

  • to the operating system that the program has terminated without errors,

  • whereas any other number would be returned as an error code. These codes enable you to have multiple programs working together,

  • reading and processing each others' output codes.

  • This is relatively common practice in industry.

  • The last part of this program, and the most important part, is the printf() statement.

  • Printf is another function which is defined by the C language. It displays a message to the standard output device.

  • Thus if you run this program in a command line, it will print to that.

  • There's a couple of key things to note about the way printf is used.

  • Firstly, we have to tell the compiler where to find Printf. This is done by the include statement at the top of the program

  • stdio (standard Input/output) is part of the standard C library

  • and contains the necessary information about this function.

  • Secondly, the section included in the brackets after printf is what's known as an argument.

  • Functions can take any number of arguments, or no arguments like our main function, signified by the word void.

  • For the printf function, the argument is, as you've probably guessed,

  • what you want printed to the screen. Make sure when you pass a string of characters like this

  • to use double quotation marks, not single, for reasons we'll cover in the next video.

  • The backslash-n is what's known as a special 'escape character' and tells the printf function

  • we want a new line after this point.

  • As a quick note, this system("PAUSE") statement simply tells the computer to wait for the user

  • to press a key before continuing in the program. I've inserted it here so that when

  • when we run our program, the output window will stay open until we hit a key,

  • allowing us to see what our program is doing.

  • Finally, notice that the end of this line, and the end of the return statement, have a semicolon.

  • Forgetting this is a key mistake you'll find happens a lot when learning C,

  • and it causes problems because the compiler won't know where your lines end.

  • If you find a program isn't compiling, always double check you put semicolons at the end of all your lines,

  • notwithstanding a few exceptions we'll cover later.

  • And that's all there is to it. We can now compile and run this program, and see the output here.

  • For now, try creating this program yourself, and try putting different message in the program

  • and see how the output changes. Of course, feel free to post any questions afterwards.

  • Thank you.

Hi, my name is Alex and this is the first in a series of videos on becoming a better computer programmer.


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C言語のハローワールドコンピュータプログラミング 1: 24時間Answersチュートリアル (Hello World in C: Computer Programming 1: 24HourAnswers Tutorials)

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    Jjli Li に公開 2021 年 01 月 14 日