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DATA IN C++

Introduction to C++

C++ is a programming language that extends the basic capabilities of the C language, keeping its syntax but introducing many advanced functionalities. One of the key aspects of this language is working with data, where the basics are similar to the C language, but with significant improvements.

C++ provides flexibility and efficiency in data management through:
  • Basic data types: Inherited from the C language (eg int, float, char) for working with basic values.
  • Namespaces: Enable organization and avoidance of conflicts between function and variable names.
  • New data types: Such as bool for logical values ​​and string for working with text, which simplifies working with modern applications.
  • Constants: Defined using the const keyword, which ensure that values ​​cannot be changed during program execution.
In the following, we will take a closer look at basic and derived data types in the C++ language, the differences compared to the C language, as well as specific features such as:
  • Variable declarations and initializations,
  • Using constants,
  • Code organization through namespaces.
In the c++ language, similarly to the C language, data can be variable(s), for which it is necessary to provide memory, constant data, constants and symbolic constants. We don't reserve memory for constants, we simply use them in expressions, but for data, whether they are variable or constant, we have to do that. For example defining the integer data would be:

int a;

where the first word represents the data type, and the second the data name. Therefore, the definition of the data is required according to the following template, with the note that it is about simple data.
​data_type  name_of_data;
To watch a video lesson for solving simple examples using the "Code Block" tool, as well as examples for independent work, click on the following link: Data-examples
C++ supports the same basic data types as C, with the addition of specific types and modern concepts. Data can be:
  • Variables: Require memory reservation.
​Example:

int a; // Declaration of a variable of type int

a = 5; // Value assignment

Constant data: Declared with const or constexpr:​

constexpr double PI = 3.14159;
Boolean Type: To describe boolean data in C++ language, there is bool data type which is used for boolean type. The use of logical types is usually when branching in a program using if, if-else and if-else if-else selections.
​This type is often used in conditional expressions:
bool isEven = (a % 2 == 0);
Character type (char): The char type is used to describe characters, letters, numbers, whitespace and special characters. This is actually an integer type that occupies a data size of 1 byte.
​
​ Example of code using characters:

char c;

c='A';

cout << "ASCII character code " << c << " is " << c << endl;

Test your code in the editor!

// Write your C++ code here...

Derived data types

In addition to arrays and pointers, C++ allows working with classes, objects, and standard libraries that simplify working with complex data structures.​
​
Array type: If you need to define an array of numbers of the same type, for example, integers, use the following syntax:

int A[10];

This reserves space for 10 elements of type int. Array elements are accessed via index, starting at array[0].

Pointer type: If you need to define a pointer to data of type double, then the pointer is defined and initialized as follows:

double a;

double *pA;;//A pointer to data of type double

pA=&a;

​See more about pointers on the page: Pointers in C/C++
From derived data types, classes and functions are also used
Type void
​In the C++ language, the void type is used when a function does not return any value:
​
void function() {
// Cod of function
}

Signed and unsigned data (signed and unsigned)

Signed data can have positive and negative values, while unsigned data are always positive. By default, data in the C++ language is signed.
Examples:

int a;

signed int b;

unsigned int c;


The data range depends on the size in memory. For example, for a 32-bit int:
  • signed int: from -2,147,483,648 to 2,147,483,647
  • unsigned int: from 0 to 4,294,967,295
The first digit in marked numbers is used to determine the sign (0 for positive, 1 for negative), while the remaining digits represent the value. Other basic types, like char, can also be signed or unsigned:
unsigned char z;
Note: Float and double types cannot be signed or unsigned.

Assigning value to data

Consider the following example:

Example 1:

Enter two integers, calculate their product and display the result on the screen.​​
Solution:

int a,b;// you can split it into two rows

int a;

int b;


​Next, we assign some value to the data using the value assignment operator “=”.
See more about operators in the c++ language on the website: Operators in the C/C++ language
This does not mean equality and it is not true that the left of the “=” sign is the same as the right. Here on the left must be the memory that should receive a value and on the right is that value or some expression whose result will be stored in the memory on the left. For example let's assign some values ​​to the variables a and b:

a=7;

b=22;

​These are the numbers 7 and 22 in binary form. For simplicity, we will consider the numbers in memory as decimal numbers
7

a

22

b

If we now define another integer variable c:

int c;

​and we set the expression for multiplying the numbers a and b:

c = a * b;

the state in memory would be:
154

c

​The calculated number is stored in memory, and in order to display it on the screen, a command is needed that prints the value on the standard output (console).
It is c++ function cout from iostream header.
In the previous example, the programmer ordered a=7; and b=22; programmatically determined the value of a and b and the user of the program could not influence those values. In most cases, it is necessary to ensure that the user enters values ​​as desired, and for this it is necessary to provide a command that temporarily remembers the number typed on the keyboard by the user as a string of characters and then converts it with the appropriate input conversion in binary form. See below reading data.
​
Complete code:
​
#include <iostream>
using namespace std;

int main() {
// Declaration of variables
int a, b, c;

// Input values ​​for a and b
cout << "Enter the first number: ";
cin >> a;
cout << "Enter another number: ";
cin >> b;

// Product calculation
c = a * b;

// Display results
cout << "The product of the numbers is: " << c << endl;
return 0;
}

Constant data

​If a variable does not change its value during the program, it is defined as a constant using the const keyword.
Example:

const double e = 2.718281;

​Note: The value of the constant must be assigned during declaration.

Constant

Constants are values ​​that we use directly in the program, such as 2, 3.14 or 9.81. Although they have no reserved memory, they have their own type:

Header files​

Header files provide access to predefined functions.
Example:
  • #include <iostream> – for data input and output (cin, cout).
  • #include <cmath> – for math functions like sqrt or pow.
 
More information about headers:​ C++ Reference.

Data types in the C++ language

In C++, the basic data types are similar to those in the C language, with extensions to the boolean type bool and classes used for complex data or objects. The following table illustrates this:
Data is the basic element of processing in programs, and in C++, data types are extended compared to C.

The data type in C++ determines the set of values a variable can hold and the operations that can be performed on it.

Data Type Description Memory [bits]
bool Binary data (true or false) 8
char Character data, used for storing a single character 8
wchar_t Extended character data for Unicode characters 16 or 32
short Short integer 16
int Integer 16 or 32
long Long integer 32
long long Very long integer 64
float Floating-point number with single precision 32
double Floating-point number with double precision 64
long double Floating-point number with extended precision 80 or 128
As can be seen from the previous tables, the C: programming language does not have a built-in bool type. Boolean values ​​are usually represented by int (0 for false, any non-zero value for true).
C++ programming language: Introduces the type bool with the values ​​true and false. It improves code readability and clarity.
​

An example of using a bool variable in C++

#include <iostream>
using namespace std;

int main() {
bool isValid = true;
if (isValid) {
cout << "Value is true!" << endl;
} else {
cout << "Value is false!" << endl;
}
return 0;
}
Here is an if command which, based on the logical variable (bool type) isValid, checks its value, and if it is correct, the command is executed: cout << "The value is true!" << endl;
which prints the text: "The value is true", and if the isValid variable has the value false, then the text "The value is false" is printed.​
The cout and cin commands will be described in the text below.

Difference between classes and objects in C and C++ programming languages

  • C: Classes are not supported. Data and functions are organized using structs and functions.
  • C++: Introduces classes, which enable object-oriented programming. Classes combine data and methods into a single unit, support encapsulation, inheritance and polymorphism.

An example with classes and objects in C++

#include <iostream>
#include <string>
using namespace std;

// Definition of the Student class
class Student {
public:
// Fields of the Student class
string name;
int age;

// Method to introduce the student
void introduce() {
cout << "Hello, I am " << name << " and I am " << age << " years old." << endl;
}
};

// Main function
int main() {
// Creating a Student object
Student s1;
// Assigning values to the object's fields
s1.name = "Mark";
s1.age = 20;

// Calling the introduce method
s1.introduce();
return 0;
}

I/O data streams in C++

Input conversion to C++ (cin):

​The cin object is used to input data in the C++ language and comes from the <iostream> library. Input is accomplished using the extraction operator (>>), which takes values ​​entered from the keyboard and stores them in variables.

Example:

#include <iostream>
using namespace std;

// Main function
int main() {
// Define a variable
int broj;

// Print a message to the screen
cout << "Enter a number: " << endl;

// Input a number
cin >> broj;

// Display the entered number
cout << "You entered: " << broj << endl;

return 0;
}

Output conversion to C++ (cout):

The cout object, also from the <iostream> library, is used to print data. The insertion operator (<<) sends data to the standard output (usually the screen). Can be used chained to print multiple values.

Example:

cout << "Hello, " << "world!" << endl;

Dataflows in C++:​

In C++, cin and cout work with data streams:
  • cin is the input stream for reading data.
  • cout is the output stream for sending data.
These streams allow for type conversion, buffering, and error checking.
Note: You can extend the explanation with examples with formatted input (getline) and output.
Read more about it in the articles: C Strings as well as Strings in C/C++
When the command is executed:

 cout << "Hello, " << "world!" << endl;
​
 here's what happens:
  1. cout object: cout is an object of the ostream class, which is used to print data to the standard output (most often the screen).
  2. Operator <<: This is an overloaded insertion operator. It passes the values ​​on the right-hand side into the data stream that cout handles.
  3. Data Stream: "Hello," is first sent to the data stream associated with cout. Then the operator << is applied again with "holy!", adding it to the existing stream.
  4. endl: This manipulator adds a newline character (\n) and immediately flushes the stream, ensuring that the data is displayed.
Data conversion
  • "Hello," and "Holy!" are const char* type strings. The stream automatically recognizes their type and passes them to the ostream::operator<< method which knows how to process strings.
  • If other data types were used (eg int or double), the << operator would call the appropriate function to convert those types to text. ​

Example with different types:
cout << "Number: " << 42 << ", Real number: " << 3.14 << endl;
The number 42 is converted to the text form "42", and 3.14 to "3.14" before inserting into the stream.
Purpose: 
Together, the << operator and flow cout enable flexible, type-safe data output in C++, relying on function overloading to support different data types.

​Declaration and initialization of different data types

In the C and C++ programming languages, variables must be declared before we can use them. Declaration includes defining the data type and variable name, while initialization involves assigning an initial value to the variable.

Example of declaration and initialization of basic data types

The following example illustrates the declaration and initialization of various data types in C++:
#include <iostream> // Include library for input/output
#include <iomanip> // For output formatting

int main() {
// Integer types
int a = 10; // Declaration and initialization of an integer
short b = 5; // Short type
long c = 1000000; // Long type

// Real numbers
float pi = 3.14f; // Float type (shorter decimal precision)
double e = 2.71828; // Double type (longer decimal precision)

// Characters
char ch = 'A'; // A single character

// Boolean type
bool isValid = true; // Logical value

// Output results using std::cout
std::cout << "Integers: " << a << ", " << b << ", " << c << std::endl;
std::cout << "Real numbers: " << std::fixed << std::setprecision(2) << pi << ", " << std::setprecision(5) << e << std::endl;
std::cout << "Character: " << ch << std::endl;
std::cout << "Boolean value: " << std::boolalpha << isValid << std::endl;

return 0;
}
Explanation:
#include <iostream>:
  • Used for input/output via std::cout and std::cin.
#include <iomanip>:
  • Allows control over formatting, such as decimal precision (std::setprecision) and fixed format (std::fixed).
std::boolalpha:
  • Displays boolean values ​​(true/false) as textual representation instead of numeric (1/0).
std::fixed and std::setprecision:
  • They are used to control the format of real numbers.

Difference between float and double

  • float uses 4 bytes of memory and allows for lower precision (approximately 6 to 7 decimal places).
  • double uses 8 bytes of memory and allows for higher precision (approximately 15 to 16 decimal digits).

Example

#include <iostream> // For input and output
#include <iomanip> // Required for setprecision

int main() {
// Float and double variable declarations
float x = 0.123456789f; // Float type
double y = 0.123456789; // Double type

// Set precision and print float value
std::cout << std::fixed << std::setprecision(9);
std::cout << "Float value: " << x << std::endl;

// Set precision and print double value
std::cout << std::fixed << std::setprecision(16);
std::cout << "Double value: " << y << std::endl;

return 0;
}
Explanation:
  1. #include <iomanip>
    This header allows using functions like std::setprecision to set the number of significant digits when printing.
  2. std::fixed 
    Sets the output of numbers to fixed decimal format, thus preventing scientific notation.
  3. std::setprecision(9) and std::setprecision(16)
    Specifies the number of digits after the decimal point.
  4. Difference between float and double
    float: Displays 6-7 significant digits.
    double: Displays 15-16 significant digits.

The result of program execution:

float value: 0.123456791

double value: 0.1234567890000000

Practical use of different types

  • Use float when you need less precision and want to save memory (eg in graphics applications or games).
  • Use double when you need high precision (eg in scientific or financial applications).
Differences in Memory and Size of Basic Data Types

This table shows the basic data types, the memory size they occupy, and their value ranges.

Data Type Memory [bytes] Value Range
char 1 -128 to 127 (or 0 to 255 for unsigned)
int 4 -2,147,483,648 to 2,147,483,647
float 4 ±3.4e−38 to ±3.4e+38
double 8 ±2.2e−308 to ±1.7e+308
short 2 -32,768 to 32,767
long 8 -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807

Namespace in C++

In C++, a namespace is a mechanism that enables code organization and prevents conflicts between identifiers (eg names of functions, classes, or variables) that have the same name but are used in different contexts.
A namespace is defined using the namespace keyword. Everything declared within a namespace belongs to that space and can only be called with the appropriate qualifier (namespace name as a prefix).

Example: 

#include <iostream> // For input and output

// Definition of two namespaces
namespace MySpace {
void display() {
std::cout << "Function in MySpace" << std::endl;
}
}

namespace AnotherSpace {
void display() {
std::cout << "Function in AnotherSpace" << std::endl;
}
}

int main() {
// Calling functions from different namespaces
MySpace::display();
AnotherSpace::display();

return 0;
}
Output:

Function in MySpace

Function in AnotherSpace

The official word using

The official word using is used for:
  1. Introducing a namespace into the current environment, which simplifies access to the members of that space.
  2. Declaration of individual namespace members.

Example 1: Using the entire contents of the namespace

#include <iostream> // For input and output
using namespace MySpace;

namespace MySpace {
void display() {
std::cout << "Using MySpace without prefix" << std::endl;
}
}

int main() {
// Direct call since MySpace is imported
display();

return 0;
}

Example 2: Introducing only one function from a namespace

#include <iostream> // For input and output
using namespace MyNamespace;

namespace MyNamespace {
void function1() {
std::cout << "Function 1" << std::endl;
}
void function2() {
std::cout << "Function 2" << std::endl;
}
}

int main() {
// Direct call for function1()
function1();

// Direct call for function2() must use namespace
MyNamespace::function2();

return 0;
}

Examples for practice

  1. Enter the radius of the circle and calculate the area
  2. Load the sides of the trapezoid and calculate the area.
  3. Load time in seconds and print in hh:mm:ss format​

Solutions:

Solution of example 1:

We solve the task in 4 steps:

First we need to define the data we need: The program needs the user to enter the radius, and the program needs to calculate the area of ​​the circle. In order to define these data, we will give them names and set the data type for real numbers (double). So the first command:

double r,P;


With this, we reserved memory for two data of type double which we marked with r and with P

The second step is to allow the user to enter the radius. For input, we use the cin method found in the file iostream

We will include this file using the directive #include for including files and write this at the top of the document

#include <iostream>

This file also contains the cout method for printing data and text to the console.

Before entering, we print a message to the console so that the user knows what to enter. For printing, we use the cout method, which actually represents the output conversion. Input conversion is achieved using the cin method. This second step is:

#include <iostream>
using namespace std;

int main() {
// Declare a variable for radius
double r;
// Prompt the user to enter the radius
cout << "Please enter the radius of the circle: " << endl;
cin >> r;
return 0;
}
In the third step, we calculate the area using the known formula for the area of ​​a circle. For multiplication, it is mandatory to use the "*" operator, while the symbolic constant is defined by the preprocessor directive #define in the upper part of the file.

In the 4th step, a message with the value of the area is printed on the screen, which is read from the memory marked in this program with P. For the output conversion, the %f format is used for data of type double.​
#include <iostream>
using namespace std;

int main() {
// Declaration of variables
double r, surface;

// Input value for radius
cout << "Enter the radius of the circle: " << endl;
cin >> r;

// Calculating the area of ​​a circle
area = 3.14159 * r * r;

// Print the results
cout << "The area of ​​the circle is: " << area << endl;
return 0;
}

Solution to Example 3:

​We solve the task in 4 steps:
Here the user enters the time in seconds which should be an integer

int totalSeconds;

// Input value for time in seconds
cout << "Enter time in seconds: " << endl;
cin >> vrSec;

​In order to get minutes and hours from this number, we will use the % operator, which gives the remainder of the division of two whole numbers, as well as the "/" operator, which gives the result of the division without a decimal part, that is, the whole number rounded to the first smaller value.  To get the number of whole hours in the total number of seconds we divide
time in seconds and 3600, vrSek/3600, and to get how many seconds are left we use "%", so vrSek % 3600.
Code that does this:

int hh, totalSeconds;

hh = vrSec / 3600;

totalSeconds=totalSeconds% 3600;

​In case the time entered is 7400s, h would be 2 hours, because 7500/2=2, if we round to the first smaller integer, while 300s would remain undivided. It is the result of operation 7200%3600=300;
In a similar way, they would get minutes from the remaining number of seconds (ostSek), but in this case they would take 60 as the divisor because 1min=60sec;

int mm;

mm = totalSeconds/ 60;

totalSeconds = totalSeconds% 60;

The rest would now remain seconds that should not be divided further. Finally to display the time we use printf formatted to display 2 digits for hours, minutes and time. In the case of single-digit numbers, it displays 0 as a prefix. So:

cout << hh << mm << totalSeconds<< endl;

Complete code:
#include <iostream>
using namespace std;

int main() {
// Variable declaration
int totalSeconds, hh, mm, ss;

// Input time in seconds
cout << "Enter time in seconds: " << endl;
cin >> totalSeconds;

// Calculate hours, minutes, and seconds
hh = totalSeconds / 3600;
totalSeconds = totalSeconds % 3600;
mm = totalSeconds / 60;
ss = totalSeconds % 60;

// Output result in hh:mm:ss format
cout << "Time: " << hh << ":" << mm << ":" << ss << endl;
return 0;
}
​Output:
Solution of the task
Figure 1: Solution of the task "formatted time"-output
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