# C Constants

Constants are the terms that can't be changed during the execution of a program. For example: 1, 2.5, "Programming is easy." etc. In C, constants can be classified as:

### Integer constants

Integer constants are the numeric constants(constant associated with number) without any fractional part or exponential part. There are three types of integer constants in C language: decimal constant(base 10), octal constant(base 8) and hexadecimal constant(base 16) .

Decimal digits: 0 1 2 3 4 5 6 7 8 9

Octal digits: 0 1 2 3 4 5 6 7

Hexadecimal digits: 0 1 2 3 4 5 6 7 8 9 A B C D E F.

#### Example

```Decimal constants: 0, -9, 22 etc
Octal constants: 021, 077, 033 etc
Hexadecimal constants: 0x7f, 0x2a, 0x521 etc
```
Note
• You can use small caps a, b, c, d, e, f instead of uppercase letters while writing a hexadecimal constant.
• Every octal constant starts with 0 and hexadecimal constant starts with 0x in C programming.

### Floating-point constants

Floating point constants are the numeric constants that has either fractional form or exponent form.

```-2.0
0.0000234
-0.22E-5
```

### Character constants

Character constants are the constant which use single quotation around characters. For example: 'a', 'l', 'm', 'F' etc.

### Escape Sequences

Sometimes, it is necessary to use newline(enter), tab, quotation mark etc. in the program which either cannot be typed or has special meaning in C programming. In such cases, escape sequence are used. For example: \n is used for newline. The backslash( \ ) causes "escape" from the normal way the characters are interpreted by the compiler.

Escape SequencesCharacter
\bBackspace
\fForm feed
\nNewline
\rReturn
\tHorizontal tab
\vVertical tab
\\Backslash
\'Single quotation mark
\"Double quotation mark
\?Question mark
\0Null character

### String constants

String constants are the constants which are enclosed in a pair of double-quote marks.

#### Example

```"bad"                  //string constant
""                     //null string constant
"      "               //string constant of six white space
"y"                    //string constant having single character.
"Earth is circle\n"      //prints string with newline
```

### Enumeration constants

Keyword enum is used to declare enumeration types.

#### Example

`enum color {yellow, green, black, white};`