# Integer Constant in C language

## 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

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