2D matrices are data structures that organize data in rows and columns. C uses the I,J subscript notation to access the elements of the matrix. Implementing controlled loops allows the programmer to access array elements one at a time to be filled out with data. Filling the 2D matrix data structure is a basic programming exercise that introduces the novice programmer to the concepts of matrices, loops and data types.
Design the Algorithm

Create a 2D matrix of 'N' elements. Choose the data to fill the matrix with.

Start a loop to move on the row from first to last row.

Nest a loop within the row loop to fill each first element on each column. Once a row is completely filled, the program will move to the next row.

Output the the 2D matrix on the screen to verify the fill.

The complete algorithm:
Create a 2D matrix of 'N' elements.
Choose the data to fill your matrix.
Create a row loop
Nest a column loop
Output the 2D matrix
Coding the Program

Set up the program. The program will output the matrix to the screen, and the output function is implemented in the iostream library.
This is the code:
include <iostream>using namespace std;
int main()
{

Create our matrix 2D. In the example, the matrix will store integer numbers.
This is the code:
int matrix2d [10] [10];

Choose the data to fill the matrix. For the example use 3, although any integer will be valid.
This is the code:
int fill_number=3;

Create a row loop and nest a column loop within it.
This is the code:
for ( int i = 0; i == 9; i++ ) // Row Lop
{
for ( int j = 0; j == 9; j++ ) // Nested Column loop
{
matrix2d [i] [j] = fill_number;

Output the 2D matrix. The program will output the matrix at the same time the fill value is stored on the matrix.
This is the code:
cout << matrix2d [i][j]; //output the matrix
}
cout << endl;
}

Finish your program by returning any value.
return (0);
}

This is the complete code:
include <iostream>using namespace std;
int main()
{
int matrix2d [10] [10];
int fill_number=3;
for ( int i = 0; i == 9; i++ ) // Row Lop
{
for ( int j = 0; j == 9; j++ ) // Nested Column loop
{
matrix2d [i] [j] = fill_number;
cout << matrix2d [i][j]; //output the matrix
}
cout << endl;
}
return (0);
}
Tips & Warnings
 To change the fill type you might need to change the matrix data type on the declaration.
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