In a program, a name May be assigned to a data item. If it remains the same, throughout the program execution, then we say that the value of name is a constant. Thus, constant (literals) is a value, written into a program instruction that does not change during the execution of a program. There are three types of constants as below:

• String constant
• Numeric constant
• Character constant

String Constant

A string constant or literal is a sequence of alphanumeric characters enclosed in  double quotation marks the maximum length of a string constant is limited to 255 characters. Each string constant is automatically added with a terminating character ‘\0’.Thus the string “abc” will actually be represented as “abc\0” in the memory and its size is 4 characters.

Numeric Constant

Numeric constant has a constant value in number. The value of the constant can be positive or negative. There are 4 types of numeric constants as follows.

1. Integer Constant: – Integer constants are whole numbers. An integer constant may be either a short integer or long integer.
2. Floating Point Constant: – A floating point constant has a real value. It may be written in two forms called the fraction form such as 0.3 and the other as exponent form such as 3.7e12.
3. Octal Constant: – Octal numbers are the integer numbers with a base 8. The digits allowed in this system are 0 to 7.
4. Hex Constant: – Hex decimal numbers are integer numbers to the base 16. The digits allowed in this system are 0 to 9 and letters A to F.

Character Constant

Character constant is either a single alphabet or a single digit or a single special symbol enclosed within a pair of single quotation mark, such as ‘A’, ‘a’, ‘.’, ‘?’.