シャドーイング練習: you will never ask about pointers again after watching this video - 動画で英語スピーキングを学ぶ
レッスンを作成中...
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One of the hardest things for new programmers to learn is pointers.
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Whether it's pointers by themselves, pointers that point to arrays, or pointers that point to pointers, Something about this concept just drives people crazy.
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And if you're a new programmer, well, you're not alone.
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I was one of those people when I learned C back in the day, and like you, I was eager to understand.
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In this video, I'll show you what a pointer is so you can fully understand how they work, the syntax of pointers so you can easily read them,
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and finally, why everyone cares so much about pointers and what they're used for.
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Before we start, if you're new here, hit that subscribe button and while you're at it leave a like.
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I put out videos demystifying topics like this and much more on a weekly basis.
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What is a pointer?
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The question that's been asked since the beginning of time.
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well, maybe not that long, but computer science students have been asking this question for a while.
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Pointers are not that complicated, and let me show you why.
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To understand what a pointer is, we need to first understand how memory works.
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So here I've laid out an example of memory.
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Memory in our example has two features: an address, and a value.
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The address is the location of the memory, meaning where that memory lives.
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And the value of that memory is the data stored at that location, meaning what memory lives there.
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So for example, if I put a four here, What does that mean?
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All that means is that the value 4 lives at location hex 1000.
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Easy.
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And the notation in C, for example, may be int x equals four, which gets allocated to that memory on the stack, and now that number lives there.
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So what happens now if at another location I put the number hex 1000 at address hex 1004?
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I've just created a pointer.
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You may be thinking, low level learning, how is this possible?
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That's just a number at a location.
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Well guys, that's the secret.
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A pointer is just a value that happens to be an address.
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Mind blown.
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By setting the value of one variable equal to the address of another, that variable now points to the other.
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For new programmers, though, most of the time, that isn't as easy as it seems.
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One of the most common issues new programmers have with pointers is the syntax used to create them.
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The combination of stars and ampersands and arrows and more stars creates a lot of confusion, so let's break this down using our previous example.
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In our last example, we made an integer x whose value was 4 at location hex 1000.
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After that, we made a pointer that lived at address hex 1004, whose value was $1000.
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So how do we do that in C?
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We can do that using two lines of code, and I'll break them down part by part.
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The first line is int x equals four.
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This line is pretty straightforward.
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The first part, integer, is the type of the variable, which is 4 bytes wide, and this will matter later in the video.
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The second part is the name.
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Nothing special here, just the variable name x.
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And then after that, we put an equal sign, which when describing C, we can verbalize the equal sign to is C set to.
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Finally, the value 4.
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So the final sentence we've come up with is, Integer whose name is X is set to the value 4.
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Okay.
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Easy part over, next is the hard part.
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To make a pointer to x like we did in our example, I would say the following line of C: int *px is equal to ampersand x.
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Now I know that sounds pretty crazy, a little scary, Let's break it down piece by piece.
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From left to right, we can see the type again, starting with int.
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But next we see the dreaded Asterisk.
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What does that mean?
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When an asterisk is placed next to a type, it modifies the type, meaning that our variable is now a pointer to an integer.
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So our variable here points to a four byte value.
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Next, the variable's name which is Px or pointer to x, You can name it whatever you want, but this is a good habit using "P" to denote that it's a pointer.
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and then after that are equal sign, which again means is set to.
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Ah, and then the next dreaded character, the Ampersand.
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Whenever you see an ampersand just think in your head the address of.
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So this means the address of x.
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Our final sentence here is, Int pointer.
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P X is set to the address of X.
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So, what does this do for us?
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Well now by using the pointer, we have a way of accessing x by reference instead of by value.
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So for example, if we wanted to copy the value of x to a new variable using that pointer, we could do that pretty easily with this new bit of code.
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We'll say that int y equals *px.
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Now what is this code doing?
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Let's break it down.
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Again, y, just like x, is a normal integer, so no pointers yet.
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We say that Y is set to, using that equal sign, uh oh, the asterisk again.
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Remember how last time I said when we see an asterisk, it's used to modify a type if a type is near it?
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Well, here there is no type.
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When it's used alone this way, the asterisk is referred to as a "d" reference.
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The dereference means go to the address pointed to by the pointer and grab that value.
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So, because px points to x, The dereference will go and grab that value and it will set Y equal to x.
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So when reverbalizing C, when you see an asterisk by itself, you can say "the thing pointed to by."
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This would mean that the final verbalization of this line of C is
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integer y is set to the thing pointed to by p x.
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By doing this, we can pass around X by reference instead of value.
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And why that matters, I'll explain in the next part of the video.
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The final concept that could use people the most when learning about pointers is why does anyone use them?
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The syntax is confusing, my programs crash all the time when I use them, why does anyone bother?
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Well, the answer is because we have to.
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To avoid making code that is impossible to read or unscalable, we break down functions based on the action that they perform,
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So here I have a small snippet of C where I have a function that updates the age of a person structure.
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The problem is that the structure I'm editing is not in scope of the editing function.
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To get around this, we pass the struct by reference so that now the pointer to the structure
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is in scope of update struct and can therefore be edited.
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Using pointers like this keeps our code clean and understandable while reducing the amount of space that we use by not copying.
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Another reason that pointers are inevitable when coding in C is the idea of using static versus dynamic memory allocation.
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static allocation is typically a variable that goes onto the stack, a place that is always in scope for the function that is running it.
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However, when you're using dynamic allocations that come from the heap through malloc or sbreak or other kinds of memory allocators,
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you are going to get a pointer to memory that is out of scope.
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If you ever want to be able to use this kind of memory, you need to know how pointers work.
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The primary difference between dynamic and static allocations is
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that static allocations are things
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that are known to have a fixed size at compile time
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whereas dynamic allocations can be changed in size as the program runs.
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Here you see I allocate a string of 100 bytes to be pulled from the heap
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But that 100 bytes could have come from a user input or something else.
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If you're having a hard time with C, don't be discouraged.
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Pointers do take a minute to master, but once you get them, you'll know it and you'll feel like a real low level wizard when you do.
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Guys, I had a fun time making this video.
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If you enjoyed this, do me a favor, hit like, hit subscribe, and I'll see you next week.
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Take care.
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このレッスンの語彙とスピーキングのポイント
この動画には、シャドーイング用の文が103文、単語が1434語あります。 音声の長さは7:59です。 話す速さは速く、1分あたり約180語です。音のつながりや弱く発音される音が多くなります。 英語の頻出3,000語に含まれる単語は81%だけなので、語彙は難しめです。
この動画の重要語彙
動画に出てくるやや難しい単語15語を、発音と意味つきで紹介します。
- pointer /ˈpɔɪn.təɹ/ (名詞) — 指し棒. One who points.
- variable [ˈvæɹ.i.ə.bl̩] (形容詞) — 可変, 変えられる. Able to vary or be varied.
- dynamic /daɪˈnæm.ɪk/ (形容詞) — 動的. Changing; active; in motion.
- static /ˈstæt.ɪk/ (形容詞) — 静的. Unchanging; that cannot or does not change.
- programmer /ˈpɹoʊɡɹæmɚ/ (名詞) — プログラマー. One who writes computer programs.
- edit /ˈɛdɪt/ (動詞) — 編集する. To change a text, or a document.
- syntax /ˈsɪn.tæks/ (名詞) — 統語論, 構文論. A set of rules that govern how words are combined to form phrases and sentences.
- stack /stæk/ (名詞) — 塚. A large pile of hay, grain, straw, or the like, larger at the bottom than the top, sometimes covered with thatch.
- subscribe /səbˈskɹaɪb/ (動詞) — 購読する. To write (one’s name) at the bottom of a document; to sign (one's name).
- dread /dɹɛd/ (名詞) — 恐怖. Great fear in view of impending evil; fearful apprehension of danger; anticipatory terror.
- topic /ˈtɑpɪk/ (名詞) — 話題, テーマ. A subject; a theme; a category or general area of interest.
- complicated /ˈkɑm.plɪˌkeɪ.tɪd/ (形容詞) — 複雑な. Difficult or convoluted.
- refer /ɹɪˈfɜː/ (動詞) — 問い合わせる. To direct the attention of (someone toward something).
- string /stɹɪŋ/ (名詞) — 紐. A long, thin and flexible structure made from threads twisted together.
- scary /ˈskɛə.ɹi/ (形容詞) — 怖い. Causing fear or anxiety
動画に出てくる句動詞
- do in (動詞) — やる. To kill or end; to defeat.
注意したい発音
話し手はyou're, I'll, I'veなど、短縮形や弱形を20回使っています。聞こえたとおりの短い形で発音しましょう。
- 「sh」と「zh」の音: allocation /ˌæl.əˈkeɪ.ʃən/, confusion /kənˈfjuːʒən/, notation /noʊˈteɪʃən/
- 長い単語（アクセントの位置に注意）: allocation /ˌæl.əˈkeɪ.ʃən/, complicated /ˈkɑm.plɪˌkeɪ.tɪd/, inevitable /ɪˈnɛvɪtəbəl/, allocator /ˈæl.ə.keɪ.tə/, demystify /diːˈmɪstɪfaɪ/
この動画での練習方法
- まず声を出さずに動画を最後まで聞き、知らない単語をメモします。
- まず0.75倍速で一文ずつシャドーイングし、慣れてきたら通常の速度に戻します。
- 自分の声を録音して元の音声と比べます。pointer, variable, dynamicなどの単語に特に注意しましょう。
この動画の文法
話し手がよく使っている文型を、動画の実際の表現とともに紹介します。
| 文型 | 動画での表現 |
|---|---|
| 受動態 be + 過去分詞 — 誰がするかより、何が起きるかに焦点を当てる | been asked · is set · is placed |
| 現在完了形 have/has + 過去分詞 — 過去の出来事が今も関係している | I've laid · I've just created · we've come |
| 関係詞節 who / which + 節 — 人や物について情報を加える | variable, which is · name which is |
シャドーイングとは？英語上達に効果的な理由
シャドーイング（Shadowing）は、もともとプロの通訳者養成プログラムで開発された言語学習法で、多言語習得者として知られるDr. Alexander Arguelles によって広く普及されました。方法はシンプルですが非常に効果的：ネイティブスピーカーの英語を聞きながら、1〜2秒の遅延で声に出してすぐに繰り返す——まるで「影（shadow）」のように話者を追いかけます。文法ドリルや受動的なリスニングと異なり、シャドーイングは脳と口の筋肉が同時にリアルタイムで英語を処理・再現することを強制します。研究により、発音精度、抑揚、リズム、連音、リスニング力、そして会話の流暢さが大幅に向上することが確認されています。IELTSスピーキング対策や自然な英語コミュニケーションを目指す方に特におすすめです。