# C++中具有用户定义大小的2D矢量vector

2021年3月9日16:17:36 发表评论 675 次浏览

2D向量是

## CPP

// CPP program
#include <iostream>

/* Vectors belong to a C++ library
called STL so we need to import
it first! */
#include <vector>
using namespace std;
int main()
{
/*
In the case of a normal vector we initialize it as:

1. vector<datatype> variable_name

Now in the case of a 2D vector all we do is create
a vector of datatype vector.

We simply replace "datatype" with "vector<int>":

1. vector<vector<int>> variable_name

That's literally it! We just created a 2D vector!
On line 23 below we declare an actual 2D vector
named "vect".
*/

vector<vector< int >> vect;

return 0;
}

## CPP

/* C++ code to demonstrate a 2D vector
with elements(vectors) inside it. */
#include <iostream>
#include <vector>
using namespace std;

int main()
{
/*
Below we initialize a 2D vector
named "vect" on line 12 and then
we declare the values on
line 14, 15 and 16 respectively.
*/

vector<vector< int >> vect
{
{1, 2, 3}, {4, 5, 6}, {7, 8, 9}
};

/*
Now we print the values that
we just declared on lines
14, 15 and 16 using a simple
nested for loop.
*/

for ( int i = 0; i < vect.size(); i++)
{
for ( int j = 0; j < vect[i].size(); j++)
{
cout << vect[i][j] << " " ;
}
cout << endl;
}

return 0;
}

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## CPP

/*
C++ program to demonstrate a 2D vector where
each of its elements is of different size.
*/
#include <iostream>
#include <vector>
using namespace std;
int main()
{
/*
We initialize a 2D vector
named "vect" on line 16 with
different number of values
in each element.
*/

vector<vector< int >> vect
{
/* Element one with 2 values in it. */
{1, 2}, /* Element two with 3 values in it. */
{4, 5, 6}, /* Element three with 4 values in it. */
{7, 8, 9, 10}
};

/*
Now we print the vector that we
just defined using a simple
nested for loop.
*/

for ( int i = 0; i < vect.size(); i++)
{
for ( int j = 0; j < vect[i].size(); j++)
{
cout << vect[i][j] << " " ;
}
cout << endl;
}
return 0;
}

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Input : Number of rows : 5
Number of columns in rows :
2 3 4 5 1
Output : 1 2
1 2 3
1 2 3 4
1 2 3 4 5
1

Input : Number of rows : 3
Number of columns in rows :
3 2 1

Output : 1 2 3
1 2
1

2D向量通常被视为内部带有"行"和"列"的矩阵。实际上, 它们实际上是2D矢量的元素。

## CPP

/*
C++ program to create a 2D vector where
every row has a certain number of values
as defined by the user.(On line 13)
*/

#include <iostream>
#include <vector>
using namespace std;
int main()
{

/* Here we tell how many rows
the 2D vector is going to have. */
int row = 5;

/* We define the number of values
each row is supposed to have. */
int colom[] = {5, 3, 4, 2, 1};

/*
We now create a vector of vector with size
equal to row.
*/

vector<vector< int >> vec(row);
/*
On line 21 we created a 2D vector and assinged
it a capacity of "row"(in this case 5) units.
*/

/*
Now we will proceed to create the sturture of
our 2D vector by assigning the value of rows and
columns through a nested for loop.
*/

for ( int i = 0; i < row; i++)
{
/* Declaring the size of the column. */
int col = colom[i];

/*
On the 43rd line we declare the
i-th row to the size of the column.
We create a normal vector of capacity "col" which
in every iteration of the for loop will define the
values inside of each row.
*/
vec[i] = vector< int >(col);
for ( int j = 0; j < col; j++)
{
vec[i][j] = j + 1;
}
}

/*
We now finally use a simple nested for loop
to print the 2D vector that we just created above.
*/

for ( int i = 0; i < row; i++)
{
for ( int j = 0; j < vec[i].size(); j++)
{
cout << vec[i][j] << " " ;
}
cout << endl;
}
return 0;
}

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1 2 3
1 2 3 4
1 2
1

" n"

" m"

## CPP

// CPP program
#include <iostream>
#include <vector>
using namespace std;
int main()
{
int n = 3;
int m = 4;

/*
We create a 2D vector containing "n"
elements each having the value "vector<int> (m, 0)".
"vector<int> (m, 0)" means a vector having "m"
elements each of value "0".
Here these elements are vectors.
*/
vector<vector< int >> vec( n , vector< int > (m, 0));

for ( int i = 0; i < n; i++)
{
for ( int j = 0; j < m; j++)
{
cout << vec[i][j] << " " ;
}
cout<< endl;
}

return 0;
}

0 0 0 0
0 0 0 0
0 0 0 0

" n"

" b"

## CPP

// CPP program
#include <iostream>
#include <vector>
using namespace std;
int main()
{
int n = 4;
int m = 5;

/*
Create a vector containing "n"
vectors each of size "m".
*/
vector<vector< int >> vec( n , vector< int > (m));

for ( int i = 0; i < n; i++)
{
for ( int j = 0; j < m; j++)
{
vec[i][j] = j + i + 1;
}
}

for ( int i = 0; i < n; i++)
{
for ( int j = 0; j < m; j++)
{
cout << vec[i][j] << " " ;
}
cout << endl;
}

return 0;
}

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