Integer literals may be expressed in a variety of formats. The sections below describe the rules for each format and provide examples.
Decimal (base 10)
Rules
- Cannot start with 0 (except for 0 itself), that would make it octal.
- Cannot include a decimal point - that would make it floating point, even if the fractional part is 0.
- Cannot include commas or spaces.
- Must use only the digits zero-nine.
- May be preceded by a minus sign "-".
Examples of Valid Decimal Integers
Examples of Invalid Decimal Integers
32,767 |
25.0 |
1 024 |
0552 |
7A |
Hexadecimal (base 16)
Rules
- Must begin with 0x or 0X.
- May use digits zero-nine and the letters A-F or a-f (not case sensitive).
- Cannot include a decimal point.
- Cannot include commas or spaces.
- May be preceded by a minus sign "-".
Examples of Valid Hexadecimal Integers
0x |
0x1 |
0x0A2B |
0x12 |
0xBEEF |
Yes, 0x is legal and represents a value of 0. However, nobody uses 0x alone, except perhaps in The International Obfuscated C Code Contest.
Examples of Invalid Hexadecimal Integers
Octal (base 8)
While octal is still part of the ANSI/ISO C specification, almost no one uses it anymore.
Rules
- Must begin with 0.
- Must use only the digits zero-seven.
- Cannot include a decimal point.
- Cannot include commas or spaces.
- May be preceded by a minus sign "-".
Examples of Valid Octal Integers
Examples of Invalid Octal Integers
Binary (base 2)
ANSI C does not specify a format for binary integer literals. However, this quasi-standard notation is supported by many compilers for embedded microcontrollers. If your code must be ANSI compliant, do not use this notation.
Rules
- Must begin with 0b or 0B.
- Must use only the digits zero-one.
- Cannot include a decimal point.
- Cannot include commas or spaces.
- May be preceded by a minus sign "-".
Examples of Valid Binary Integers
0b |
0b1 |
0b0101001100001111 |
Examples of Invalid Binary Integers