C++ Constants/Literals

Constants refer to fixed values that the program may not alter and they are called literals.

Constants can be of any of the basic data types and can be divided into Integer Numerals, Floating-Point Numerals, Characters, Strings and Boolean Values.

Again, constants are treated just like regular variables except that their values cannot be modified after their definition.

Integer literals

An integer literal can be a decimal, octal, or hexadecimal constant. A prefix specifies the base or radix: 0x or 0X for hexadecimal, 0 for octal, and nothing for decimal.

An integer literal can also have a suffix that is a combination of U and L, for unsigned and long, respectively. The suffix can be uppercase or lowercase and can be in any order.

Examples of various types of Integer literals

```85 // decimal
0213  // octal
30  // int
30u // unsigned int
30l // long
30ul // unsigned long
```

Floating-point literals

A floating-point literal has an integer part, a decimal point, a fractional part, and an exponent part. You can represent floating point literals either in decimal form or exponential form.

While representing using decimal form, you must include the decimal point, the exponent, or both and while representing using exponential form, you must include the integer part, the fractional part, or both. The signed exponent is introduced by e or E.

Boolean literals

There are two Boolean literals and they are part of standard C++ keywords:

• A value of true representing true.
• A value of false representing false.

You should not consider the value of true equal to 1 and value of false equal to 0.

Character literals

Character literals are enclosed in single quotes. If the literal begins with L (uppercase only), it is a wide character literal (e.g., L'x') and should be stored in wchar_t type of variable . Otherwise, it is a narrow character literal (e.g., 'x') and can be stored in a simple variable of char type.

A character literal can be a plain character (e.g., 'x'), an escape sequence (e.g., '\t'), or a universal character (e.g., '\u02C0').

There are certain characters in C++ when they are preceded by a backslash they will have special meaning and they are used to represent like newline (\n) or tab (\t). Here, you have a list of some of such escape sequence codes:

Escape sequence Meaning
\\ \ character
\' ' character
\" " character
\? ? character
\b Backspace
\f Form feed
\n Newline
\r Carriage return
\t Horizontal tab
\v Vertical tab
\ooo Octal number of one to three digits
\xhh . . . Hexadecimal number of one or more digits

Example to show few escape sequence characters

```#include<iostream>
using namespace std;
int main()
{
cout <<"Hello\tWorld\n\n";
}
```
Output
`Hello World`

String literals

String literals are enclosed in double quotes. A string contains characters that are similar to character literals: plain characters, escape sequences, and universal characters.

You can break a long line into multiple lines using string literals and separate them using whitespaces.

Defining Constants

There are two simple ways in C++ to define constants:

• Using #define preprocessor.
• Using const keyword.

The #define Preprocessor

#define preprocessor to define a constant:

Syntax

`#define identifier value`

Example

```#include<iostream>
using namespace std;
#define LENGTH 10
#define WIDTH  5
int main()
{
int area;
area =LENGTH *WIDTH;
cout <<area;
}
```
`50`

The const Keyword

You can use const prefix to declare constants with a specific type as follows:

Syntax

```consttype variable = value;
```

Example

```#include<iostream>
using namespace std;
int main()
{
int area;
const int LENGTH 10
const int WIDTH  5
area = LENGTH * WIDTH;
cout <<area;
}
```
`50`