# Software # C++ Variables, Literals and Constants In this tutorial, we will learn about variables, literals, and constants in C++ with the help of examples. *Content from [https://www.programiz.com/cpp-programming/variables-literals.](https://www.programiz.com/cpp-programming/variables-literals)* ## C++ Variables In programming, a variable is a container (storage area) to hold data. To indicate the storage area, each variable should be given a unique name (identifier). For example, ``` int age = 14; ``` Here, age is a variable of the `int` data type, and we have assigned an integer value 14 to it. **Note:** The `int` data type suggests that the variable can only hold integers. Similarly, we can use the `double` data type if we have to store decimals and exponentials. We will learn about all the data types in detail in the next tutorial. The value of a variable can be changed, hence the name **variable**. ``` int age = 14; // age is 14 age = 17; // age is 17 ```

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### Rules for naming a variable

- A variable name can only have alphabets, numbers, and the underscore `_`. - A variable name cannot begin with a number. - It is a preferred practice to begin variable names with a lowercase character. For example, name is preferable to Name. - A variable name cannot be a [keyword](https://www.programiz.com/cpp-programming/keywords-identifiers). For example, `int` is a keyword that is used to denote integers. - A variable name can start with an underscore. However, it's not considered a good practice.

**Note:** We should try to give meaningful names to variables. For example, first\_name is a better variable name than fn.

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## C++ Literals Literals are data used for representing fixed values. They can be used directly in the code. For example: `1`, `2.5`, `'c'` etc. Here, `1`, `2.5` and `'c'` are literals. Why? You cannot assign different values to these terms. Here's a list of different literals in C++ programming.

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### Integers An integer is a numeric literal(associated with numbers) without any fractional or exponential part. There are three types of integer literals in C programming:

- decimal (base 10) - octal (base 8) - hexadecimal (base 16)

For example: ``` Decimal: 0, -9, 22 etc Octal: 021, 077, 033 etc Hexadecimal: 0x7f, 0x2a, 0x521 etc ``` In C++ programming, octal starts with a `0`, and hexadecimal starts with a `0x`.

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### Floating-point Literals A floating-point literal is a numeric literal that has either a fractional form or an exponent form. For example:

`-2.0` `0.0000234` `-0.22E-5` **Note:** `E-5 = 10^-5`

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### Characters A character literal is created by enclosing a single character inside single quotation marks. For example: `'a'`, `'m'`, `'F'`, `'2'`, `'}'` etc.

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### Escape Sequences Sometimes, it is necessary to use characters that cannot be typed or has special meaning in C++ programming. For example, newline (enter), tab, question mark, etc. In order to use these characters, escape sequences are used.

Escape Sequences	Characters
`\b`	Backspace
`\f`	Form feed
`\n`	Newline
`\r`	Return
`\t`	Horizontal tab
`\v`	Vertical tab
`\\`	Backslash
`\'`	Single quotation mark
`\"`	Double quotation mark
`\?`	Question mark
`\0`	Null Character

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### String Literals A string literal is a sequence of characters enclosed in double-quote marks. For example:

`"good"`	string constant
`""`	null string constant
`" "`	string constant of six white space
`"x"`	string constant having a single character
`"Earth is round\n"`	prints string with a newline

We will learn about strings in detail in the C++ string tutorial.

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## C++ Constants In C++, we can create variables whose value cannot be changed. For that, we use the `const` keyword. Here's an example: ``` const int LIGHT_SPEED = 299792458; LIGHT_SPEED = 2500 // Error! LIGHT_SPEED is a constant. ``` Here, we have used the keyword `const` to declare a constant named `LIGHT_SPEED`. If we try to change the value of `LIGHT_SPEED`, we will get an error. A constant can also be created using the `#define` preprocessor directive. We will learn about it in detail in the C++ Macros tutorial. # C++ Data Types In this tutorial, we will learn about basic data types such as int, float, char, etc. in C++ programming with the help of examples. In C++, data types are declarations for variables. This determines the type and size of data associated with variables. For example, ```C++ int age = 13; ``` Here, age is a variable of type `int`. Meaning, the variable can only store integers of either 2 or 4 bytes.

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## C++ Fundamental Data Types The table below shows the fundamental data types, their meaning, and their sizes (in bytes):

Data Type	Meaning	Size (in Bytes)
`int`	Integer	2 or 4
`float`	Floating-point	4
`double`	Double Floating-point	8
`char`	Character	1
`wchar_t`	Wide Character	2
`bool`	Boolean	1
`void`	Empty	0

Now, let us discuss these fundamental data types in more detail.

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### 1. C++ int

- The `int` keyword is used to indicate integers. - Its size is usually 4 bytes. Meaning, it can store values from **-2147483648 to 2147483647**. - For example,

```C++ int salary = 85000; ```

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### 2. C++ float and double

- `float` and `double` are used to store floating-point numbers (decimals and exponentials). - The size of `float` is 4 bytes and the size of `double` is 8 bytes. Hence, `double` has two times the precision of `float`. To learn more, visit C++ float and double. - For example,

```C++ float area = 64.74; double volume = 134.64534; ``` As mentioned above, these two data types are also used for exponentials. For example, ```C++ double distance = 45E12 // 45E12 is equal to 45*10^12 ```

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### 3. C++ char

- Keyword `char` is used for characters. - Its size is 1 byte. - Characters in C++ are enclosed inside single quotes `' '`. - For example,

```C++ char test = 'h'; ``` **Note:** In C++, an integer value is stored in a `char` variable rather than the character itself. To learn more, visit [C++ characters](https://www.programiz.com/cpp-programming/char-type).

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### 4. C++ wchar\_t

- Wide character `wchar_t` is similar to the `char` data type, except its size is 2 bytes instead of 1. - It is used to represent characters that require more memory to represent them than a single `char`. - For example,

```C++ wchar_t test = L'ם' // storing Hebrew character; ``` Notice the letter L before the quotation marks.

**Note:** There are also two other fixed-size character types `char16_t` and `char32_t` introduced in C++11.

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### 5. C++ bool

- The `bool` data type has one of two possible values: `true` or `false`. - Booleans are used in conditional statements and loops (which we will learn in later chapters). - For example,

```C++ bool cond = false; ```

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### 6. C++ void

- The `void` keyword indicates an absence of data. It means "nothing" or "no value". - We will use void when we learn about functions and pointers.

**Note:** We cannot declare variables of the `void` type.

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#### Putting it all together Run the following repl to see its results. Looking at the `main.cpp` file, a range of variables of different data types are declared at the top. `cout` is used with the `+` operator to output the sum of two integers. `cout` is also used to display a message that includes the contents of the string variables, and lastly an if statement is used to present a message based on which letter is stored in the char variable. ##### Try doing each of the following, running the between each change: 1. Change the string variables to reflect your name 2. Change the values of the integers 3. Change the operator used in the output to `*` 4. Change the letter stored in the char variable to a grade you would like to receive 5. Change the integer variables to float, and assign decimal values.

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## C++ Type Modifiers We can further modify some of the fundamental data types by using type modifiers. There are 4 type modifiers in C++. They are:

1. `signed` 2. `unsigned` 3. `short` 4. `long`

We can modify the following data types with the above modifiers:

- `int` - `double` - `char` ---

### C++ Modified Data Types List

Data Type	Size (in Bytes)	Meaning
`signed int`	4	used for integers (equivalent to `int`)
`unsigned int`	4	can only store positive integers
`short`	2	used for small integers (range -32768 to 32767)
`unsigned short`	2	used for small positive integers (range 0 to 65,535)
`long`	at least 4	used for large integers (equivalent to `long int`)
`unsigned long`	4	used for large positive integers or 0 (equivalent to `unsigned` `long int`)
`long long`	8	used for very large integers (equivalent to `long long int`).
`unsigned long long`	8	used for very large positive integers or 0 (equivalent to `unsigned long long int`)
`long double`	12	used for large floating-point numbers
`signed char`	1	used for characters (guaranteed range -127 to 127)
`unsigned char`	1	used for characters (range 0 to 255)

Let's see a few examples. ```C++ long b = 4523232; long int c = 2345342; long double d = 233434.56343; short d = 3434233; // Error! out of range unsigned int a = -5; // Error! can only store positive numbers or 0 ```

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## Derived Data Types Data types that are derived from fundamental data types are derived types. For example: arrays, pointers, function types, structures, etc. We will learn about these derived data types in later tutorials. # data science topis **Topic : Introduction to data science** -

Data scientist skills

Data scientist responsibilities

data vs information

**Topic : Presenting data science projects** - Planning - performing - Data visualization - Data analytics **Topic : Ethics of data science** - Code of ethics - Privacy, transparency and security - Consent - Fairness and Algorithms **Topic : Data manipulation** - What is data manipulation? - Tools - Techniques **Topic : Artifical intelegence** - AI history - Three phases of AI - Learning processes - Strong AI vs. weak AI - AI ethics - Case studies - business - education - healthcare - finance **Topic : Machine Learning** - Mathematics for machine learning - Linear algebra and discrete mathematics - Multivariate calculus - Statistics - Machine learning algorithms - Machine learning pipeline - Optimisation for machine learning **Topic : Deep learning** - Deep learning vs machine learning - Natural language processing (NLP) - Self learning - Self-learning agents in games # Python Strings