Tableaux : tableaux dynamiques multidimensionnels

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Del curso dictado por École Polytechnique Fédérale de Lausanne

Initiation à la programmation (en C++)

214 calificaciones

École Polytechnique Fédérale de Lausanne

Initiation à la programmation (en C++)

214 calificaciones

Ce cours initie aux bases de la programmation en utilisant le langage C++ : variables, boucles, fonctions, ... Il ne présuppose pas de connaissance préalable. Les aspects plus avancés (programmation orientée objet) sont donnés dans un cours suivant, «Introduction à la programmation orientée objet (en C++)». Il s'appuie sur de nombreux éléments pédagogiques : vidéos sous-titrées, quizz dans et hors vidéos, exercices, devoirs notés automatiquement, notes de cours.

De la lección

Tableaux

Après plusieurs semaines sur les traitements, nous revenons cette semaine et les suivantes sur les données pour présenter des types de données plus avancés que les types de base. Cette semaine : les tableaux qui permettent de regrouper plusieurs données de même type.

Tableaux : introduction9:34

Tableaux : déclaration et initialisation des vector7:44

Tableaux : utilisation des vector15:44

Tableaux : exemples simples (vector)6:53

Tableaux : fonctions spécifiques vector11:50

Tableaux : tableaux dynamiques multidimensionnels8:35

Tableaux : array16:04

Conoce a los instructores

Jean-Cédric Chappelier
Dr.
School of Computer and Communication Sciences
Jamila Sam
Dr
School of Computer and Communication Sciences

In a previous episode,

we have seen one-dimensional dynamic array,

that is, dynamic arrays of values.

For example, the different ages of this course's students.

How should we proceed in order to represent

multi-dimensional arrays?

For example, an array of all the grades

of all the students for for all exams.

For example, we could build an array for one student

containing the different grades for the different exams.

Then build a second array for another student,

also containing the grades for all their exams.

Then build a third array and so on.

Globablly, we would thus have

an array of ... arrays.

Each element of this array being an array of grades itself.

For example, let us suppose

that we wish to have an array for 5 students.

And that, for example,

each of these students will have passed 6 exams.

Finally, we thus have 6 grades.

We will thus end up with a dynamic array of 5 arrays of 6 marks.

We will thus declare a dynamic array

which we will call "tab".

This dynamic array will itself contain

a dynamic array of integers.

The integers are our grades.

The dynamic array of integers

is the array of a student's grades.

And the dynamic array of the dynamic arrays of integers

is the array of the arrays of all the students.

We will initialize it to the number of students.

We have 5 students here.

What is each of these 5 element actually?

It is itself a dynamic array of integers,

representing a student's grades.

Each of these elements will contain 6 grades.

Finally, we have a dynamic array

containing 5 dynamic arrays of 6 grades.

The syntax used here in order to give an initial value

to each array of grades, each student,

each subarray

is the same as the one we have already encountered

during the copy of an array.

It is the anonymous array.

It is like writing : " vector <int> tab2 ",

initialized with 6 ints, all with the initial value zero

except that we have suppressed the name.

We thus end up with an anonymous array.

Here, we did not name

our dynamic array of 6 null integers.

Now, let us look at our dynamic array

of dynamic arrays of integers

that we have declared here and called "tab".

" tab[i] " is thus an element of this dynamic array

corresponding to an array of grades.

" tab[i] " is thus a itself a dynamic array of integers,

It corresponds to the type we have given here :

a dynamic array of integers.

Also, we have given the initial value here.

Thus "tab[i]", for example "tab[0]"

is this array of 6 integers.

" tab[i][j] " is the element at the position "j".

Therefore, it means that it is the (j+1)th element of the "tab[i]" array.

Thus, starting from this array here,

the dynamic array of dynamic arrays of integers,

if we take "tab[i]",

" tab[i] " is itself a dynamic array of integers.

We are looking for the (j+1)th element,

the element at the position "j".

As usual, we represent " tab[i] [j] "

as the element on the (j+1)th row and (j+1)th column.

We do not need to forget that, here, we have

a dynamic array of dynamic arrays of integers.

The dynamic aspect of these rows is still there;

indeed, each of the rows may have elements

added or removed from it.

Finally, this means that

the dynamic array of dynamic arrays

does not necessarily have rows of the same size.

For example, we may very well

have a first size for " tab[0] " here

(it is indeed a dynamic array of integers),

a different size for " tab[1] "

(a second dynamic array of integers)

and so on.

Let us now thoroughly look at this example.

We will thus declare

a dynamic array of dynamic arrays of integers.

We will call it, for example, "tableau". (TN: "tableau" means "array").

If we wish to initialize it to the value of the example

we have drawn here,

what we will do is to

give an initial value as a list of elements.

Each of these elements being

a dynamic array of integers.

We can see the first row here.

Then the second row

and so on for the third row

and the fourth row

of our dynamic array of dynamic arrays of integers.

This initialization corresponds exactly

to the drawing here on the right.

A little digression regarding the syntax :

When we declare a dynamic array of dynamic array of integers,

we need here to glue together the closing of the two types

with the two "greater than" signs,

glued together like this.

This is only allowed in C++ 2011.

If need to write it in a compiler

which is not C++ 2011,

then you will have to put a blank space between these two signs here.

Indeed, the syntax with the two "greater than" signs

glued together like this is not supported

by older compilers.

Now, let us see how to go through this array.

For that, we will use a C++ 2011 loop

with the colon.

The array we wish to go through

is "tableau" here.

Here, we are declaring the variable which will go through the rows.

We call it "ligne". (TN: "ligne" means "line" or "row").

This will let us go through the array row by row.

Then, going through a row,

we will explore all the elements of a given row.

For example, if we are on the first row,

we will then go through the different elements of this line here

in a second "for loop".

This loop will, this time,

go through the array "ligne" we have declared here

which is a given line.

We will go through this row, naming it

"element".

This "element" variable will go through the different elements of a row.

This is what we have written here.

We can then use this "element" variable

in order to go through the different elements

of a row.

Finally, let us illustrate the fact that the elements of the array

are indeed dynamic arrays

by giving the size of the different rows

of the different dynamic arrays.

To that end, we will use

a usual "for loop".

As usual, we will start with " i ",

declared as a "size_t" to the value 0.

As long as " i " is less than the array size

(the array we are talking about,

the initial array, here),

as we have done countless times,

" i " will be incremented 1 by 1.

What we will do is to print

" tableau[i] ".

Thus, we will print "tableau[0].size() ", "tableau[1].size() " and so on.

Then, we can use, as such,

"tableau[i]" which as array

".size()", returning the size of the array.

The following will thus be printed :

5 for " tab[0].size() " ,

3 for " tab[1].size() " ,

2 for " tab[2].size() " ,

and, finally, 3 again

for " tab[3].size() " .

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