Two-dimensional arrays - matrix in the programming language C and C++

A matrix in programming is a way to organize data in a grid format, making it easy to store values in rows and columns. In C and C++, we use two-dimensional arrays to represent matrices. For example, an array with dimensions [3][3] forms a 3x3 grid.

Defining a Two-Dimensional Array

In C or C++, a matrix of integers with 3 rows and 3 columns is defined as:
int matrix[3][3];
This creates a grid with space for 9 integers in total.

Example Code: Initializing and Printing a Matrix

Here’s an example to initialize and print a 3x3 matrix. Each line of code includes comments for clarity.
#include <stdio.h>

int main() {
// Define a 3x3 matrix
int matrix[3][3] = { 
        {1, 2, 3},
        {4, 5, 6},
        {7, 8, 9}
    };

// Nested loop to print each element
for(int i = 0; i < 3; i++) {             // Loop over rows
for(int j = 0; j < 3; j++) {         // Loop over columns
            printf("%d ", matrix[i][j]);      // Print element at row i, column j
        }
        printf("\n");                         // New line after each row
    }
return 0;
}Explanation of Key Parts In order to store a set of data, in the form of a matrix, i.e. data placed in several rows and columns, we will use a two-dimensional array.
​Suppose we want to print a series of the first 100 natural numbers, but to be printed in 10 rows and 10 columns, as in the picture below:​two dimensional aaray: Matrix display of 100 numbers in 10 rows
Figure 1: Matrix display of 100 numbers in 10 rows
In order to print this, we use the nested "for" loop:​Ispisivanje prvih 100 prirodnih brojeva matrično
Figure 2: Matrix display of 100 numbers in 10 rows-code
To put these numbers in the memory, we should either introduce 10 sets of 10 elements or if we want to remember all the data in one variable, then we would use a two-dimensional array (matrix)
int matrix [10] [10];
This is an integer matrix with 10 rows and 10 columns.
Access to a certain element that we say is in row 3 and column 5 would be:
matrix [3] [5]
The previous example would have been a little changed

C

int matrix[10][10];
for( int i = 0; i < 10; i++)
{
for(int j = 0; j < 10; j++)
{
int a=10 * i +(j+1);
matrix[i][j]=a;
printf("%2d ",a);
}
printf("\n");//New row
}

C++

int matrix[10][10];
for( int i = 0; i < 10; i++)
{
for(int j = 0; j < 10; j++)
{
int a=10 * i +(j+1);
matrix[i][j]=a;
cout<< a<
}
cout << endl;//New row
}
In each cycle, the calculated number is placed in the matrix in the i-th row and j-th column.​

If we know in advance the numbers to be placed in the matrix


For example. grades from some subjects for more students could be placed in a matrix:

int estimates [3] [5] = {{2,3,2,2,4,5,5,4}, {2,3,2,2,4,5,5,4}, {2,3 , 2,2,4,5,5,4}}

Dimensions should be placed in square brackets, although they are determined by the series that we initialized in the matrix.
So, 3 rows and 8 columns. Here it can be concluded that the matrix is ​​actually a series of elements where these elements are also arrays.
Each column and row have their index with which the matrix element can be accessed. In the previous example, rows are numbered with indexes 0-2, and columns indexes 0-7.

Example: Calculate the average grade for all students from the predefined sets

​In order to calculate the average, we must first collect all the elements of the matrix and divide it with the number of elements. We need it ugly for the loop:

C

void average(){
int estimates[3][8]={ {2,3,2,2,4,5,5,4}, {2,5,2,5,4,5,5,4}, {2,4,4,2,4,3,5,4} };
int sum=0;
double average;
for(int i=0; i < 3; i++){
for(int j=0; j < 8; j++){
sum=sum + estimates[i][j];
printf("%d ",estimates[i][j]);
}
printf("\n");
}
printf("Average:\n");
average=sum/(3.0*8.0);
printf("%.2f\n",average);
}

C++

void average(){
int estimates[3][8]={ {2,3,2,2,4,5,5,4}, {2,5,2,5,4,5,5,4}, {2,4,4,2,4,3,5,4} };
int sum=0;
double average;
for(int i=0; i<3; i++){
for(int j=0; j<8; j++){
sum=sum + estimates[i][j];
cout << estimates[i][j] << " ";
}
cout << endl;
}
cout << "Average:" << endl;
average=sum/(3.0*8.0);
cout << average;
}

After starting:

Two dimensional array in c: Calculating the average-execution of the console application
Figure 3: Calculating the average-execution of the console application

​Suggested topic: Classes and objects

Object-oriented programming is based on the concept of objects. It is an approach that enables solving problems by mutual cooperation of facilities within the program. One of the most popular programming languages ​​is JAVA.

Example: Calculate the average grade for each student separately from the predefined sets

In order to calculate the average for each student, then we must separately compose each order of the grade and divide it with the number of elements of each inner string, because the rank each grade represents a student's grades. The average will now be a number of numbers:

C

int grades[3][8]={ {2,3,2,2,4,5,5,4}, {2,5,2,5,4,5,5,4}, {2,4,4,2,4,3,5,4} };
double sum=0;
double average[3];
for(int i=0; i < 3; i++)
{
for(int j=0; j<8; j++)
{
sum=sum+grades[ i ][ j ];
printf("%.2f ",grades[ i ][ j ]);
}
average[ i ]=sum/8;
sum=0;
printf("\n");
}
printf("Average:\n");
for(int i=0; i < 3; i++)
printf("%d. %.2f"\n",(i + 1),average[ i ]);

C++

int grades[3][8]={ {2,3,2,2,4,5,5,4}, {2,5,2,5,4,5,5,4}, {2,4,4,2,4,3,5,4} };
double sum=0;
double average[3];
for(int i=0; i<3; i++)
{
for(int j=0; j<8; j++)
{
sum=sum+grades[ i ][ j ];
cout << grades[ i ][ j ] << " ";
}
average[ i ]=sum/8;
sum=0;
cout << endl;
}
cout << "Average:" << endl;
for(int i=0; i < 3; i++)
cout << i + 1 << " . " << average[ i ] << endl;
​After starting:
Two dimensional array in c: Calculating the average score of the individual execution of the program
Figure 4: Calculating the average score of the individual execution of the program

One dimensional array

A one-dimensional array, or simply an array, is a complex data type that contains several consecutive elements of the same type. Read more about it on the web page:
Arrays in C/C++One dimensional array
Figure 5: One dimensional array

Entering data and placement in the two dimensional array

In the previous example, the assessment matrix was assigned. In order for the user to load the matrix, the number of rows and columns should be pre-loaded.​

C

int m,n;
scanf("%d%d",&m,&n);
int matrix[m][n];

for( int i = 0; i < m; i++)
{
for(int j = 0; j < n; j++)
{
scanf("%d",matrix[i][j]);
}
}

C++

int m,n;
cin >> m >> n;
int matrix[m][n];

for( int i = 0; i < m; i++)
{
for(int j = 0; j < n; j++)
{
cin >> matrix[i][j];
}
}
Example: Attack jumper
Load the position of the jumper in the chess m and n and determine which jumper field is attacking. If the columns are marked 1-8 and lines A-H, mark the field codes that the jumper attacks. Mark the remaining fields with an asterisk, except where the jumper is located.
​
Input
The lines and columns representing the jump position 1 <= m <= 8, 1 <= n <= 8

Output
Field codes in those fields that jumpers attack, empty in the field where the jumper is, stars on the other		 Example: Attack jumper
Figure 6: Example: Attack jumper
Instruction:
To print the corresponding text to the appropriate field, we will use a matrix whose elements are a string type. Since the chessboard is a dimension of 8 * 8, and the index in the matrix starts from zero, we will create a matrix of order 9 * 9.

    string board [9] [9];

It needs to go through all the matrix elements in a row. Since the last row in the matrix is ​​the first row in the chessboard, it should be set up to nest for the loop as follows:
for (int i = 8; i> = 1; and--)
{
        for (int j = 1; j <= 8; j ++)
        {
...
        }
}
When it arrives at the position i = m, j = n, then it is necessary to print the codes in the fields that are attacked by the jumper. For example. position i = m + 2, j = n-1 and  j = n + 1, etc.		 Example:
Input
4
4
OutputExample Jumper Attack - Execution
Figure 7: Example Jumper Attack - Execution

Interactive task

Goal of the Exercise
The user can modify the values ​​in the matrix or resize the matrix in code to better understand working with two-dimensional arrays.

Instructions for the user

Task: Create and populate a two-dimensional array in C++.
Description: Initialize a matrix of 3 rows and 4 columns and enter user-modifiable values. Then display the array as a matrix on the console.
Example Code
Use the following code as a base. Modify the values ​​in the matrix and run the code to see the changes:
​Useful site Geek For Geeks:​https://www.geeksforgeeks.org/multidimensional-arrays-c-cpp/
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