Integer Constant in C programming

Integer constant 

‘‘What is an integer? Explain giving example.”

Definition: An integer constant is a whole number without any decimal point. No extra characters are allowed other than + and –sign. If + and – are present, they should precede the  number. An integer constant can be classified into three types as shown below.

Integer Constants are

Decimal : e.g: 120,14,-1, etc
Octal   : e.g : 070,012,-040, etc.
Hexadecimal : e.g. 0xBA, 0x3B etc


Now, let us explain decimal integer with example.
Definition: A decimal integer can be any combination of digits from ‘0’ to ‘9’. No extra characters are allowed other than ‘+’ and ‘–’ sign. If ‘+’ and ‘–’are present. Then they should precede the integer. For example, 100,-7,+989 etc.The following are invalid:

Decimal Integers	Validity	Reasons for Invalidity
10,000	invalid	Comma is not allowed.
0.5	invalid	Decimal point is not allowed.
10 20	invalid	Space is not allowed.
085	invalid	Should not start with the digit 0.
32768	invalid	Out of range for 16 bit machine.
-32769	invalid	Out of range for 16 bit machine.

Now let us see ‘‘What is an octal number? Explain giving example.’’

Definition: An octal integer constant can be any combination of digits from ‘0’ to ‘7’ with a Prefix 0(digit zero).No extra characters are allowed other than preceding ‘+’ and ‘- ’ sign. For Example, 01612, 034567, -0765 etc. are valid. The following are invalid:

Octal Integers	Validity	Reasons for invalidity
7,000	Invalid	Comma is not allowed.
0.075	Invalid	Decimal point is not allowed.
10 20	Invalid	Space is not allowed.
085	Invalid	8 is invalid in octal.
275	Invalid	Should have a prefix 0.

Now, let us see ‘‘What is a hexadecimal number? Explain giving example.’’

Definition: An hexadecimal integer constant can be any combination of digits from ‘0’ to ‘9’ along with the letters ‘A’ to ‘F’ or ‘a’ to ‘f’. This constant has be preceded OX or OX. For example, 0x18A, OXB, OXFFF etc. are valid. The following are invalid hexadecimal constant:

Hexadecimal Integers	Validity	Reasons for invalidity
10,000	invalid	Comma is not allowed.
0xIJ	invalid	I and J are invalid characters.
Ox123	invalid	Should be preceded with 0(zero) not O(Oh.)
O1234	invalid	Should be preceded with 0x or OX.

Note: usually decimal integers are used in programming. Octal and hexadecimal  are rarely used.

Floating point constant