Signed integers can be of these types (the int after short, or long is optional):
signed char c = 127; /* required to be 1 byte, see remarks for further information. */
signed short int si = 32767; /* required to be at least 16 bits. */
signed int i = 32767; /* required to be at least 16 bits */
signed long int li = 2147483647; /* required to be at least 32 bits. */
Version ≥ C99
signed long long int li = 2147483647; /* required to be at least 64 bits */
Each of these signed integer types has an unsigned version.
unsigned int i = 65535;
unsigned short = 2767;
unsigned char = 255;
For all types but char the signed version is assumed if the signed or unsigned part is omitted. The type char constitutes a third character type, diﬀerent from signed char and unsigned char and the signedness (or not) depends on the platform.
Diﬀerent types of integer constants (called literals in C jargon) can be written in diﬀerent bases, and diﬀerent width, based on their preﬁx or suﬃx.
/* the following variables are initialized to the same value: */
int d = 42; /* decimal constant (base10) */
int o = 052; /* octal constant (base8) */
int x = 0xaf; /* hexadecimal constants (base16) */
int X = 0XAf; /* (letters 'a' through 'f' (case insensitive) represent 10 through 15) */
Decimal constants are always signed. Hexadecimal constants start with 0x or 0X and octal constants start just with a 0. The latter two are signed or unsigned depending on whether the value ﬁts into the signed type or not.
/* suffixes to describe width and signedness : */
long int i = 0x32; /* no suffix represent int, or long int */
unsigned int ui = 65535u; /* u or U represent unsigned int, or long int */
long int li = 65536l; /* l or L represent long int */
Without a suﬃx the constant has the ﬁrst type that ﬁts its value, that is a decimal constant that is larger than INT_MAX is of type long if possible, or long long otherwise.
The header ﬁle <limits.h> describes the limits of integers as follows. Their implementation-deﬁned values shall be equal or greater in magnitude (absolute value) to those shown below, with the same sign.