Matrix in Functions

In this tutorial from our C++ ebook, we will learn how to work with matrix and functions, learning to declare, invoke and use these two important topics together.

How to Pass a Matrix to a Function

In the study of arrays, we saw that there are some ways to declare the header of functions with arrays as parameters, as follows:

type func(tipo *array);
type func(tipo array[tamanho]);
type func(tipo array[]);

In other words, just pass the pointer (*array - we will study more ahead) or just with the pair of open brackets (array[]).

In the case of two-dimensional arrays, we need to specify the number of columns in the array we are sending:

void func(int arr[][COLUMN]);

You see, the number of rows is not mandatory (we can even pass), but the number of columns is.
Let's declare and initialize a 2x2 matrix and then send it to the show() function, which will simply display it as a table, see how our code looks:

#include <iostream>
using namespace std;

void show(int arr[][2], int row)
{
    for (int i=0 ; i<row ; i++){
        for(int j=0 ; j<2 ; j++)
            cout<<arr[i][j]<<"  ";
        cout<<endl;
    }
}

int main()
{
    int arr[][2]={ {1,2}, {3,4} };
    show(arr, 2);
    return 0;
}

Look some important things in the code above.

First, we pass the array arr[][2] to the function, with the number of columns.
But what about the number of lines? How will the function know how many lines to print the table?
It doesn't know, so we pass another parameter in the function, the integer 'row'.

C++ Matrix: Passing by Reference

All data passing to functions that involve arrays and matrix is by reference. Ever.
That is, passed an array to a function? It will directly access the array and its data, directly into memory. It is not a copy that goes to function, it is not a pass for value, ok?

That means one thing: watch out! Functions can modify the arrays, always remember that.
The code below introduces the 'init' function, which will receive an array and initialize each element of it, asking the user:

#include <iostream>
using namespace std;
const int COLS = 3;
const int ROWS = 3;

void init(int arr[][COLS], int ROWS)
{
    for(int i=0 ; i<ROWS ; i++)
        for(int j=0 ; j<COLS ; j++){
            cout << "matrix["<<i+1<<"]["<<j+1<<"]: ";
            cin  >> arr[i][j];
        }
}

void show(int arr[][COLS], int ROWS)
{
    for (int i=0 ; i<ROWS ; i++){
        for(int j=0 ; j<COLS ; j++)
            cout<<arr[i][j]<<"  ";
        cout<<endl;
    }
}

int main()
{
    int arr[ROWS][COLS];
    init(arr, ROWS);
    show(arr, ROWS);
    return 0;
}

To improve the organization, we have already defined the rows (ROWS) and columns (ROLS) as global variables of the constant type, so that there is no danger of anyone, anywhere in the code, changing their values. This makes the code clearer and safer for maintenance.

Matrix Exercise in C ++

Create a 4x4 matrix, where each row represents a student's grades, and each column is a different subject. You must create a function that will fill in the students' grades, one by one, indicating which is the subject and which is the student.

Then, your program should display, in an organized manner, the grades of each student, as well as the average of each, the class average for each subject, and the general average, of all students of all grades.

Post your solution in the comments.

Progressive C++