Name: C語言的世界你好計算機編程1：24HourAnswers教程 (Hello World in C: Computer Programming 1: 24HourAnswers Tutorials)
Uploaded: 2021-01-14T06:08:42.000Z
Duration: 6 min 11 s

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

我是Alex，這是如何成為更好的程序設計師影片系列的首部曲

未來進行式

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

情態副詞

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

這是大學裏很普遍的教學工具，和大多數商用開發語言之間有許多共通點

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

我假設大家沒有任何C語言的基礎

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

如果有需要的話，你可以自行去看其他進階的影片

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,

這13年來，我一直是個專業的程式設計愛好者

having intially started with Basic before teaching myself C.

在自修C語言之前，我學的是BASIC語言

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

我現在為財務分析軟體的銷售領導者工作

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,

每當你遇到一個新的程式語言，你就會想寫一個可以印出'Hello World'的程式

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

這通常是以程式語言寫出來的程式之中，最簡單且算得上有意義的那一個

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

現在在螢幕上就是'Hello World'程式，我們將在接下來的幾分鐘好好地把它剖析一遍

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

你可以用任何C或C++的編譯器來編譯

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

就像是我現在用的，微軟視窗作業系統下的視覺開發工具（ Visual Studio）

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

首先要注意的是：C是程序式的程式語言

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

程式由好幾個程序組成，這些程序會依照一定的流程執行

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,

你可能很想知道，電腦是如何得知從程式的哪個部份開始執行

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

答案就在你程式中名字叫作'main'的函式，程式就是從這裏開始執行的

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

main函式可以從命令列傳入參數，這些參數夾在一對小括號裏

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

main函式會傳回一個整數（在C語言中，int表示整數型別）。現在你還不必為了不知道這些術語是什麼意思而擔心

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

請注意，每一個程式裏只能有一個main函式，否則編譯器是不會放過你的

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

每個函式，包含main函式，都由完整的程式碼區塊所組成，我們會將這個區塊寫在一對大括號裏

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

這一對大括號形成函式的視野範圍

This has implications later on when you declare variables

視野範圍對我們往後宣告變數會有影響

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

變數只能存在函式的視野範圍之內、或視野範圍的裏層

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.

成對的大括號設定了程式區塊的視野範圍

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

函式由return指令來結束。如果不打算傳回具體的資訊

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

這表示該函式的回傳型別為void，這時候return指令是可以省略掉的

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

如果你把這樣的return指令省略掉，編譯器會自動幫你加上去。在學習C語言的時候

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

在須要return指令的地方，你就自己寫上去，這樣你會很清楚程式的每一個步驟

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

在這種情況下，main函式傳回一個0。這是我們的程式用來

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

通知作業系統：程式正常結束。

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

其他非0的數值則代表main函式傳回錯誤代碼給作業系統。這些代碼讓數個程式得以協同工作

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()指令是程式的最後、也是最重要的一部份

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

printf是由C語言所定義的函式，我們用printf將訊息顯示在標準輸出設備上（標準輸出設備指的是螢幕或命令提示列視窗）

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

如果這個程式在命令提示列下執行，相關的訊息就會顯示在命令提示列視窗裏

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

在使用printf函式時，有幾件事要特別注意

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

首先，我們得讓程式開頭部份的include指令負責告訴編譯器：printf函式在那裏

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

stdio（標準輸入/輸出）是C語言的標準函式庫的一部份

and contains the necessary information about this function.

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

緊接在printf之後，那一對小括號裏的一小段文字就是參數

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

函式可以完全不接收、或者接收任意數量的參數

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

你大概猜到了，printf函式的參數

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

就是那些你想要印到螢幕上的字串。當你想要傳遞字串時

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

請用雙引號，而不是單引號。下一部的影片會解釋為什麼

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

倒斜線n就是所謂的「脫逸字元」，它告訴printf函式

我們想要印出一個跳行符號到標準輸出設備上

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

這裏有個小提醒，指令system("PAUSE")要電腦等停下來等待使用者

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

在程式繼續執行下前必須按下任意鍵。我將這條指令放在這裏的目的是

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

當程式執行時，用來顯示執行結果的視窗會一直留在螢幕上，直到我們按下任意鍵才消失

allowing us to see what our program is doing.

如此一來我們就可以從容觀察我們的程式到底做了些什麼

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

最後要注意的，這一行結尾的地方，在return指令結束的地方要有一個分號

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

忘了在指令的結尾加上分號，這是在學習C語言時常犯的致命錯誤

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

因為編譯器不知道你的指令到底在哪裏結束，這是導致你的程式無法被編譯的原因之一

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

如果你的程式無法正確被編譯，請確認你是否在每條指令的結尾加上分號

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.

就是這麼簡單。我們現在編譯並執行這個程式，看看得到了什麼結果

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

現在請試著編寫自己的程式，嘗試在程式裏使用和'Hello world'不同的訊息

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

看看程式輸出的結果有什麼變化。如果有任何問題的話，請貼文發問