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.

C++ Function - What It Is, How It Works, and How to create and Use?

In this tutorial, we will begin the study of C++ Functions, where we will learn:

• What is a function?
• What is a function for?
• How to create one?
• How to use a function?

C++ Function: What It Is and What It Is For

Have you ever seen a board with some hardware, like your computer board, or the inside parts of a television, cell phone ... it's something like this:

See: There is not just one piece responsible for doing everything.
A board is a portion of small pieces doing small, very specific jobs.

Because they do very specific things, such as counting or measuring temperature, for example, we can use these little pieces on other boards, such as a car or a refrigerator.

That is, each little piece has a specific function, does something.
In C++ programming, it's the same thing: Function is a piece of stuff that does a specific thing.

Putting it best, function is a block of code, with some C++ commands inside, that does a certain task. A function can receive and return information for the caller.

It is much better, more efficient, faster, and more feasible to create a board with several small pieces, doing specific things, than a big and only piece doing something alone.

Likewise, it is not feasible to have a single block of giant code, thousands of lines, because it would be extremely difficult to work with, knowing where there are errors, where is something ... the ideal is to go breaking your program in smaller programs that make things more specific and easier to understand.

It is as if each function were a little lego. You put the pieces together and you assemble great and cool things. Your operating system, for example, works like this.

Let's learn how to create a function?

How to create a function in C++

The code syntax for creating a function is as follows:

type name(parameter_list)
{
    // Code of
    // funtion

    return something;
}

Functions may or may not return some information, such as an integer or a float.

For example:

• int function1 () {...} - returns an integer
• float function2 () {...} - returns a float
• void function3 () {...} - returns nothing

Within the parentheses, they can receive information to work with these data, are the parameters:

• void function1 (int num) {...} - Send an integer to the function and return nothing
• int function2 (int num1, float num2) {...} - Send two numbers as a parameter, an integer and a float, and return an integer.

If the function returns any data type, we use return within the code block to return the data type we declared in the function header.

Let's create the hello () function, it returns no data and receives no information, just prints hello, world! on the screen:

void hello()
{
    cout <<"Hello, world!\n";
}

How to call and use a function in C++

To call the function simply write its name, followed by parentheses and the information it should receive.

To call the function we created earlier, we simply do:
hello();

Ready. C++ goes there to get this function and execute the code that has it, see:

You can invoke (call) function 1, 10 or a million times, just do: hello() ;, without having to repeat the code 1 million times, just reuse using functions.

Example of Using C++ Functions

Let's create two functions now.
The menu() displays a menu of options about which time of day you are.

In welcome(), the user will have to type some option, which will be stored in the op variable, declared within the function.

Then, still within this function we make a treatment to display the message correctly:

#include <iostream>
using namespace std;

void menu()
{
    cout<<"What time of day is:\n";
    cout<<"1. Morning\n";
    cout<<"2. Afternoon\n";
    cout<<"3. NIght\n";
}

void welcome()
{
    int op;
    cin>>op;

    if(op==1)
        cout<<"Good morning!\n";
    else if(op==2)
        cout<<"Good afternoon!\n";
    else if(op==3)
        cout<<"Good night!\n";
    else
        cout<<"Invalid entry\n";
}

int main(int lista)
{
    menu();
    welcome();
    cout<<"Shuting down...\n";

    return 0;
}

Note that it has three functions in the code:

1. menu()
2. welcome ()
3. main ()

main() is a special function of C ++, it is automatically executed when we compile and execute our code. Inside it, we first call menu() and only when it finishes executing, it calls welcome().

Note that only after the user enters the value in welcome() and she greets you, will it end and return to main(), which displays a final closing cout.

When to use a function in C++

Ever. As much as you can.

So far in our course we have done small and simple code examples.

But when you become a professional programmer, it is normal to make systems with hundreds or thousands of lines of code, and that's when you will understand how important the concept of functions is in C++.

You should get into the habit of creating small, simple, easy-to-understand and easy-to-use functions, because whenever you start a new project, you'll use your old functions and existing C++ functions by default.

This technique is called divide and conquer, and throughout our C ++ course you will see that a large and complex program is nothing more than a bunch of small, simple, correctly connected programs that work in harmony.