Name: C++におけるベクトル (Vectors in C++)
Uploaded: 2025-05-27T13:35:34.000Z
Duration: 16 min 1 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

In this video we're going to take an introductory look at vectors.

このビデオでは、ベクターについて入門的に説明します。

Alright so let's talk a little bit about what a vector is.

では、ベクターとは何かについて少し話そう。

程度の副詞

So when we think about vectors we're just thinking about a collection of things.

だから、ベクトルについて考えるとき、私たちはただ物事の集まりについて考えているにすぎない。

Technically we say that a vector is a container object but that just simply means that it holds things of a certain type.

厳密には、ベクターはコンテナ・オブジェクトだと言うが、それは単に、ある型のものを保持するという意味に過ぎない。

So we could have a vector that has a collection of ints, doubles, strings, so anything from our primitive data types or user defined types and these could be user defined types from the standard template library or it could be user defined types that we define ourselves.

つまり、int、double、stringなどのプリミティブ・データ型やユーザー定義型、標準テンプレート・ライブラリのユーザー定義型、あるいは自分たちで定義したユーザー定義型を集めたベクトルを持つことができる。

So we have here a representation of maybe students, we could have a collection of students represented by a vector, maybe a collection of employees or a collection of books, a collection of songs or albums being represented by a vector.

生徒のコレクションをベクトルで表現したり、従業員のコレクションや本のコレクション、曲やアルバムのコレクションをベクトルで表現することもできる。

So a vector is whenever we declare it we have to specify a specific type.

つまり、ベクターは宣言するたびに特定の型を指定しなければならない。

So we cannot have like a mix and match of books and CDs and employees but we'd have a collection of a specific thing, whatever that thing may be.

だから、本やCDや従業員を寄せ集めたりすることはできない。

So that's basically what we're talking about when we talk about vectors, it's just a collection of a specific type.

つまり、ベクターについて話すとき、基本的に私たちが話しているのはそういうことだ。

Okay so now that we have a basic definition of what a vector is let's look at actually visualizing vectors and also defining some of the vocabulary associated with vectors.

さて、ベクトルとは何かという基本的な定義ができたところで、実際にベクトルを視覚化し、ベクトルに関連する語彙を定義してみよう。

And what we'll find out is we have some similar vocabulary to whenever we talked about strings.

そして、ストリングスについて話したときと似たようなボキャブラリーを持っていることがわかるだろう。

So how do we go about actually declaring a vector and bringing it into existence?

では、実際にベクターを宣言し、存在させるにはどうすればいいのか。

So assume that we want to represent maybe rainfall for a one week period of time.

そこで、1週間の降雨量を表すとする。

So we may want to declare a variable and the way we would declare a vector and the way we would do that is just use the word vector and then we could specify the type and maybe the type is double so we can have some sort of fractional part there.

変数を宣言する場合、ベクトルを宣言するのが一般的だが、その場合はベクトルという単語を使い、型を指定する。

And then we would actually give it a name so maybe the name of this vector since it's going to hold rainfall is called rainfall.

このベクトルは降雨量を保持するものなので、このベクトルの名前は降雨量と呼ぶことにします。

And we'll specify the size here inside of parentheses since we want to represent the rainfall for a one week period of time we'll use the value of seven.

ここでは、1週間の降雨量を表すため、括弧の中でサイズを指定し、その値を7とする。

So this statement here actually creates a vector of type double that's called rainfall so we can refer to this vector by this name and it's of size seven.

つまり、このステートメントでdouble型のrainfallという名前のベクトルを作成し、この名前でこのベクトルを参照することができる。

So here we have the size and here we have the type and here we have the name.

ここにサイズ、ここにタイプ、そしてここに名前がある。

Okay so out in memory we can think about having seven contiguous or adjacent spaces in memory allocated for seven doubles.

さて、メモリ上では、7つのダブルス用に7つの連続した、あるいは隣接したスペースが割り当てられていると考えることができる。

So each one of these would represent space in memory that could hold a double value.

つまり、これらのひとつひとつが、ダブル値を保持できるメモリ上の空間を表していることになる。

And what we call each one of these little spaces here associated with our vector is an element.

そして、ベクトルに関連するこれらの小さな空間をそれぞれ要素と呼ぶ。

So we have seven elements in this particular vector.

このベクトルには7つの要素がある。

The other thing associated with this vector is our, at least each one of the elements is what we call an index value.

このベクトルに関連するもう一つのことは、少なくとも各要素がインデックス値と呼ばれるものであることだ。

So the very first element has an index value of zero.

つまり、一番最初の要素のインデックス値は0である。

So we'll just put zero here and maybe I'll say that this is the index.

だから、ここにゼロを置き、これがインデックスだと言うことにしよう。

So we have zero, one, two, three, four, five, and six.

ゼロ、1、2、3、4、5、6というわけだ。

So these are just simply labeling the positions.

つまり、これらは単にポジションを表示したに過ぎない。

It's the exact same concept that we have with our strings when we were labeling the positions of the characters in that string.

これは、文字列で文字の位置をラベル付けしたときとまったく同じ概念だ。

So in our case if we're talking about rainfall and maybe we want to represent this rainfall in centimeters we may have 2.3 centimeters the first day, 1.2 and maybe zero on the next day and we have 3 centimeters, maybe 4.2, maybe 1.1 and then finally we have some sort of downpour on the last day and maybe it's 9.8 centimeters.

つまり、降雨量をセンチメートルで表すとすると、初日は2.3センチメートル、次の日は1.2センチメートル、そしてゼロかもしれない、3センチメートル、4.2センチメートル、1.1センチメートル、そして最終日は豪雨で9.8センチメートルかもしれない。

So this is the collection of data that we're wanting to represent in this particular vector.

つまり、これがこの特定のベクトルで表現したいデータの集まりだ。

And we can make use of this particular vector and access any one of our elements at any point in time so we can have direct access to any particular value in this vector.

そして、この特定のベクトルを利用して、任意の時点で任意の要素にアクセスすることができる。

And the way we do that is just via the name of the vector, so in this case rainfall, and then in square brackets we would specify the index value.

その方法は、ベクターの名前（この場合はrainfall）を指定し、角括弧で囲んでインデックス値を指定する。

So if we wanted to access the fourth element, so this would be considered the fourth element in our vector, but it's the index value, that element has the index value of three.

つまり、4番目の要素にアクセスしたい場合、これはベクトルの4番目の要素とみなされるが、インデックス値であり、その要素のインデックス値は3である。

So we would say the rainfall for the fourth day with the index value of three would be, we would be able to retrieve that through the statement or this expression rainfall open square bracket and then the index value of three closed square bracket.

つまり、4日目の降雨量をインデックス値3として、ステートメントまたはこの式で取り出すことができる。

So this is some of the basic terminology and how we go about visualizing vectors in general and again these vectors can hold any particular type so it doesn't have to just be a double or a string or an int or a float, it could be any defined type that we have.

これは基本的な用語の一部であり、一般的にベクトルを視覚化するための方法です。

So let's go ahead and go over to Eclipse and we'll take a further look at vectors and some of the syntax associated with using vectors.

それではEclipseに移動して、ベクターと、ベクターの使用に関連するいくつかの構文についてさらに見ていきましょう。

Okay so I don't have a specific problem statement here for program eight, that's what we're going to call this program, but mainly I want to just show you some syntax related to vectors and also some of the operations.

さて、プログラム8の具体的な問題文はありませんが、このプログラムをそう呼ぶことにします。

So let's go ahead and get started and do our pound include, so we'll do a pound include for iostream, we're going to make use of cout and we'll also do a pound include, this is a new impound include but it hopefully will make sense for vector, okay.

では、さっそくポンド・インクルードをしてみましょう。iostream用のポンド・インクルードをして、coutを利用します。また、ポンド・インクルードもします。これは新しいインパウンド・インクルードですが、うまくいけば、ベクターでも意味が通じます。

So our standard template library is what's providing us with support for this vector construct and we'll also do using namespace standard and then we'll get started with our main function, so int main, open paren, close paren, open brace, close brace, and here we'll actually go about creating our vector with the syntax that we saw before, so just simply the word vector, open angle bracket, it should automatically insert a close angle bracket, then you specify the type and we'll say the type here is just int and then make a space after that close angle bracket and we'll call this vector as v, you know you can name it anything, but we'll just say v for vector, open parenthesis and then we'll specify the size, so the size of the vector goes in the parenthesis here and we'll say the size of it is three, so a fairly small vector.

標準テンプレート・ライブラリはこのベクトル構文をサポートしてくれるもので、名前空間standardも使用する、すると自動的に閉じ角括弧が挿入されます。それから型を指定します。ここでは型をintとし、閉じ角括弧の後にスペースを空けて、このベクトルをvと呼びます。

And as it is right now, whenever this vector is created out in memory, it'll actually initialize each one of those elements to the value of zero if we're talking about a numeric type.

今のままでは、このベクトルがメモリ上に作成されるたびに、各要素は初期化され、数値型の場合はゼロになります。

So if we wanted to change those particular element values to something else, we could specify a particular element, do v, open square bracket and it should automatically insert a close square bracket, if we wanted to change say the first element, we'd specify zero there as the index and then use our assignment operator and maybe we'll put the value of ten there in the first element.

例えば最初の要素を変更したい場合、インデックスにゼロを指定し、代入演算子を使って最初の要素に10の値を入れる。

And we could do that for the second element, so we'll do that, maybe we'll use the value of 22 and then the third element, which would have the index value of two and we'll say that it has a value of five.

つ目の要素には22という値を使い、3つ目の要素には2というインデックス値を使い、その値は5とします。

So we now have changed each one of our elements to a different value beyond or besides what was there by default, which was zero.

つまり、各エレメントをデフォルトの値（ゼロ）とは異なる値に変更したのだ。

Now one of the operations associated with vectors is that we can actually dynamically add more elements to our vector, which is really nice because there's other container objects that are supported by C++ that doesn't allow you to dynamically change the size of it.

C++でサポートされている他のコンテナ・オブジェクトでは、ベクターのサイズを動的に変更することはできません。

So the way that we can do that, say we wanted to add another element on to the end, we could do this, we could do v and then do dot and you may get a little pop-up list or drop-down list there, it's for code completion and I'm going to start typing in push and if you want you can just select push back there and then you can select what value that you want to have placed in that last element.

例えば、最後にもう1つ要素を追加したい場合、こうすることができます。vと入力し、ドットと入力すると、小さなポップアップリストかドロップダウンリストが表示されます。

So this is actually a value that you want to have placed there, so we'll put the value of seven.

つまり、これは実際に配置したい値なので、7という値を配置します。

So that's going to be in the fourth element, the index value or the element with the index value of three.

つまり、4番目の要素、インデックス値、またはインデックス値3の要素に入ることになる。

Okay, and maybe we'll do some cout operations, so we'll do cout and we can do v dot, I'm going to just make use of another operation that's available to us and I'll use what's called front.

coutとvドットを使って、もうひとつ利用できる操作を使ってみよう。

So that will retrieve the value from the very first element, the one that's in the front, so it should be retrieving the value of ten.

つまり、一番最初の要素から値を取得することになる。

And we'll do an indel and then I'll do another cout and as you can imagine if there's a front there's also a back, so we can select that.

そして、インデルを行い、もう1つカウトを行います。ご想像の通り、表があれば裏もありますから、それを選択します。

So there's no arguments being specified there for front or back, it's just, you know, depending on how large our vector is, the back will just simply retrieve the value there that's in the very last element and the front will retrieve the value that's in the very front element.

つまり、frontやbackに引数を指定するのではなく、ベクトルの大きさに応じて、backは単純に一番最後の要素にある値を取得し、frontは一番前の要素にある値を取得するだけなのだ。

And we can also specify, you know, directly what element we want to maybe print out.

また、プリントアウトしたい要素を直接指定することもできる。

So we can do a cout and then we can do v dot at, which is similar to what we did when we were talking about strings, the at operation, so now it's associated with the vectors and maybe we want to specify two here for the, that would actually be, I guess, the third element, right?

これは、文字列について話したときにやったことと似ている。

So it's the vector that has the index value of two.

つまり、インデックス値が2のベクトルだ。

Alright, so we have that and I'm going to just do a return zero here and we'll go ahead and save this and then we'll build it, see if we get any error messages, it looks like everything compiled and linked okay and now we'll run it and see what happens.

エラーメッセージが表示されたら、コンパイルとリンクは完了したようだ。

So we got ten, seven, and five outputted, so ten was in the front, seven was in the back, because we did this push back operation here, so that's what we expected, and then five is what we expected to get from this operation here, it was the third element but with the index value of two.

10、7、5が出力されたので、10は前に、7は後ろに、ここでプッシュ・バック操作を行ったので、これは期待通りの結果だ。

So again, whenever we use the at operation we are specifying the index value.

つまり、at演算を使うときはいつも、インデックス値を指定していることになる。

Let's do one more thing here and we'll make it a fairly short function, we'll write another function that allows us to maybe print out the contents of our vector, so instead of us having to actually go through and specify every single element here line by line, if we had, you know, a hundred elements it would take a long time for us to actually write out a bunch of cout operations like we did here for every single element.

ここではもうひとつ、かなり短い関数にして、ベクトルの中身をプリントアウトできるような関数を書いてみましょう。

So what we're going to do is write a function that will actually print out each one of those values.

そこで、それぞれの値を実際に出力する関数を書くことにする。

So this is going to be a void returning function and we'll just call it maybe print vector and we'll pass to it a vector that's of type int, since vector v is of type int, and it really doesn't matter what you name it, you could name it v, you could name it, I don't know, I'll name it b, just to name it something different, just to show you that we can have it name something different than what we had here before.

ベクトルvはint型なので、int型のベクトルを渡します。vという名前でもいいですし、bという名前でもいいでしょう。

And we'll simply do a for loop, so for int i assignment statement zero, so this is our initial statement, we're just initializing that counter called i, and we'll say as long as i is less than, and we have the size operation, so we can do v dot size here, well not v, I should have said b, do v dot size, it doesn't know what v is, so v dot size, maybe that was a bad choice, b's and v's sound a lot alike, so b as in Bob, and then we'll do i plus plus.

そして単純にforループをします。for int i assignment statement zero、これが最初のステートメントで、iというカウンターを初期化しています。

So again, just looking at our for loop header, we have our initial statement here that's simply declaring a counter, we have our loop continuation condition, so this is basically specifying that we will keep looping through the body of this for loop as long as i is less than the size, which in our case right now, our vector size is four, so we should make four iterations through this loop body, and each time we go through the loop body, we need to be incrementing that counter, if we don't increment that counter, then we'll set ourselves up where we'd be infinitely going through this for loop body.

繰り返しになりますが、forループのヘッダーを見ると、ここにはカウンターを宣言しただけの初期文があり、ループの継続条件があります、ループ本体を通過するたびにカウンターをインクリメントする必要があります。カウンターをインクリメントしなければ、forループ本体を無限に通過することになります。

So we'll do c out, and then we'll specify that we want to print out the contents, so we do that by specifying again the, I keep writing the b, the name of the vector, and then whatever the index value is in between the open square bracket, closed square bracket, and then we'll I guess separate out each one of these values with a pipe symbol, so we'll use the pipe, so that should be just shift and your backslash key, that's the case on most keyboards, and make sure you add in a semicolon.

そこでc outとし、次に内容をプリントアウトするように指定します。そのためには、b、ベクターの名前を書き続け、開いた角括弧と閉じた角括弧の間にインデックス値を指定します。

One thing that I'll note here is that whenever we call this particular function, so down here I'm going to call this function print vector, and we'll pass it v, what's happening is is we actually get a copy of the vector v being passed up here to print vector.

ここでひとつ注意しておきたいのは、この関数を呼び出すたびに、つまりこの下にある関数print vectorを呼び出すときにvを渡すと、print vectorに渡されるベクトルvのコピーが実際に得られるということだ。

Now is that really needed, probably not, I think in the next video we'll actually look at the various types of parameter passing that we have available to us in C++, and we'll find out that in cases like this, we can just simply pass a reference to that vector v up here to this b, and the b will just now be an alias as opposed to just holding a brand new copy of a new vector.

次のビデオでは、C++で利用できるさまざまなタイプのパラメータ渡しを実際に見てみましょう。このような場合、単純にベクトルvへの参照をこのbに渡せばいいことがわかります。

Alright maybe the other thing that we'll do, right now we'll have a pipe symbol after every single value that we print out, but if you wanted to have a pipe symbol at the very beginning you may want to do the cout, and then just put the pipe symbol there before the for loop, and that'll ensure that you have a pipe symbol at the very beginning.

でも、もし一番最初にパイプ記号をつけたかったら、coutを実行し、forループの前にパイプ記号をつければ、一番最初に確実にパイプ記号をつけることができる。

So let's go ahead and save this program once again, and build it, and we have some mistakes here, what did I, how did I, what did I do here, expected semicolon before, oh I forgot to do a semicolon after my cout statement, ah, okay let's try building that once more.

このプログラムをもう一度保存してビルドしてみよう。ここでいくつかミスがあった。

Okay so we got past all of our errors, it did provide a warning here, or output a warning, it says comparison between signed and unsigned integer expression, so this is related to the size operation here, so the size operation isn't actually returning an int value, but it's trying to compare it to an int value, so again you could do a cast operation there and cast that to an int, but I'm going to just ignore that for now, it's not really important that we change that.

さて、これでエラーはすべて取り除かれましたが、ここで警告が表示されたり、警告が出力されたりしました。符号付き整数式と符号なし整数式の比較と書かれています。

So we've got everything building okay, and now I run this program, and we get what we had before, but we also get the contents of our vector actually being printed out.

このプログラムを実行すると、以前と同じように、ベクターの内容が実際にプリントアウトされる。

So that's pretty much it, a little bit about vectors, and we'll probably come back and discuss vectors in much more detail, and maybe have a full problem statement related to vectors and how we can use them.

ベクトルについてもう少し詳しく説明し、ベクトルとその使い方に関する完全な問題文を作成することになるだろう。