# Constants in C

Constants are those tokens in C language whose value is fixed and does not change during the execution of a program. There are various types of constants in C.

** Integer Constants**

These constants refer to a sequence of digits. Any representation can be used to specify an integer constant. Table -1 shows ways to specify an integer constant, whose value is 1234 in decimal number system, in different number systems.

Table -1: Representation of an integer in different number systems

**Real Constants**

These constants refer to those numbers which contain fractional parts like 12.34. Such numbers are called real or floating point numbers. A real constant can also be expressed in exponential or scientific notation. As an example, 12.34 can also be expressed as 1234E-2. In this form, the real number is expressed in terms of mantissa and exponent. The mantissa is either a real number or an integer and exponent is an integer number. Both can have an optional plus or minus sign. The letter E separating the mantissa and the exponent can be written in lowercase also.

** Character Constants**

These constants refer to those tokens which contain a single character enclosed within a pair of single quotes like ‘W’. The character may be a letter, number, special character or blank space. As an example, ‘5’ is a character constant while as 5 is an integer constant. Similarly, 5.0 can be treated as real constant.

Character constants are printable characters which are stored in memory as their ASCII (American Standard Code for Information Interchange) code.

**String Constants**

These constants refer to those tokens which contain a string of characters enclosed within a pair of double quotes. The characters may be letters, numbers, special characters and blank space. Examples include “Hello World!”, “123”, and so on. It should be noted “123” is a string constant while 123 is integer constant.

**Backslash Character Constants**

These constants refer to those special character constants which contain a backslash and some character enclosed within a pair of single quotes. These constants are used in output functions and are known as escape sequences. Table 1 shows the list of backslash character constants along with their interpretation.

Figure -1: ASCII Table

Table -1: List of backslash character constants in C