what are default integer values?

Question

I read somewhere that default floating point values like 1.2 are double not float.
So what are default integer values like 6 , are they short , int or long?

Answer 1

The type of integer literals given in base 10 is the first type in the following list in which their value can fit:

• int
• long int
• long long int

For octal and hexadecimal literals, unsigned types will be considered as well, in the following order:

• int
• unsigned int
• long int
• unsigned long int
• long long int
• unsigned long long int

You can specify a u suffix to force unsigned types, an l suffix to force long or long long, or an ll suffix to force long long.

Reference: C99, 6.4.4.1p5

Answer 2

Just if someone is interested:

C11 §6.4.4.1/5:

The type of an integer constant is the first of the corresponding list in which its value can be represented.

---------------------------------------------------------------------------
Suffix        Decimal Constant              Octal/Hexadecimal Constant
---------------------------------------------------------------------------
none          int                           int
              long int                      unsigned int
              long long int                 unsigned long int
                                            long long int
                                            unsigned long long int
---------------------------------------------------------------------------
u or U        unsigned int                  unsigned int
              unsigned long int             unsigned long int
              unsigned long long int        unsigned long long int
---------------------------------------------------------------------------
l or L        long int                      long int
              long long int                 unsigned long int
                                            long long int
                                            unsigned long long int
---------------------------------------------------------------------------
Both u or U   unsigned long int             unsigned long int
and l or L    unsigned long long int        unsigned long long int
---------------------------------------------------------------------------
ll or LL      long long int                 long long int
                                            unsigend long long int
---------------------------------------------------------------------------
Both u or U   unsigned long long int        unsigned long long int
and ll or LL
---------------------------------------------------------------------------

As for the prefix §6.4.4.1/3:

A decimal constant begins with a nonzero digit and consists of a sequence of decimal digits. An octal constant consists of the prefix 0 optionally followed by a sequence of the digits 0 through 7 only. A hexadecimal constant consists of the prefix 0x or 0X followed by a sequence of the decimal digits and the letters a (or A) through f (or F) with values 10 through 15 respectively.

Answer 3

There are three types of integer literals(or integer constants in the standards terminology): decimal, octal or hex and the rule are slightly different for your specific example 6 would be int but in general for decimal constants without a suffix(u, U, l, L, ll, LL) it will be based on which type can represent the value which is covered in the draft C99 standard section 6.4.4.1 Integer constants paragraph 5 which says:

The type of an integer literal is the first of the corresponding list in which its value can be represented.

so for a decimal literal without a suffix the types would be the first of:

• int
• long int
• long long int

and for octal and hex the types would be the first of:

• int
• unsigned int
• long int
• unsigned long int
• long long int
• unsigned long long int