Fundamental Datatypes

Integer numbers

• required by ANSI C to use a binary representation
• typically use two's complement arithmetic
• char
  • usually the smallest chunk of memory that can be operated on, typically an 8 bit byte
  • unsigned char uses all available bits to represent the value
  • signed char reserves one bit for a sign flag (to switch between positive and negative values)
  • on a machine with 8 bit bytes and two's complement arithmetic,
    • unsigned char can hold values between 0 and 255
    • signed char can hold values between -127 and 127
  • without a signed or unsigned qualifier, char may use whichever representation is more efficient on the target machine
  • Example declarations:
    • unsigned char a
    • signed char b
    • char ch
• int
  • minimum of 16 bits wide (usually 2 bytes)
  • just as with char, an int can be signed or unsigned
  • the signed qualifier is the default on all int types (that is, int and signed int mean the same thing, making the signed qualifier optional)
  • three sizes of int - short int, int, and long int
    • int is usually the most efficient fundamental datatype because it is normally the same size as a machine word
    • in the mid '90s, most common Unix workstations have 32 bit words and thus use 32 bit ints
    • short int is smaller than or the same size as int
    • long int is larger than or the same size as int
    • for short int and long int, the int is optional.
  • Example declarations:
    • int i
    • signed i (same as int i)
    • unsigned j
    • short smaller
    • unsigned short small
    • long large
    • unsigned long largest

<limits.h>

• machine dependent ranges for the char and int types are defined in the <limits.h> file
• minimum ranges as defined by ANSI C:

    CHAR_BIT	          8	/* number of bits in a 'char' */
    SCHAR_MIN	       -127	/* minimum value for 'signed char' */
    SCHAR_MAX	        127	/* maximum value for 'signed char' */
    UCHAR_MAX	        255	/* maximum value for 'unsigned char' */
    SHRT_MIN	     -32767	/* minimum value for '(signed) short (int)' */
    SHRT_MAX	      32767	/* maximum value for '(signed) short (int)' */
    USHRT_MAX	      65535	/* maximum value for 'unsigned short' */
    INT_MIN	     -32767	/* minimum value for '(signed) int' */
    INT_MAX	      32767	/* maximum value for '(signed) int' */
    UINT_MAX	      65535	/* maximum value for 'unsigned int' */
    LONG_MIN	-2147483647	/* minimum value for '(signed) long (int)' */
    LONG_MAX	 2147483647	/* maximum value for '(signed) long (int)' */
    ULONG_MAX	 4294967295	/* maximum value for 'unsigned long (int)' */
  

• if char is an unsigned value, these values are also defined:

    CHAR_MIN	          0
    CHAR_MAX	          UCHAR_MAX
  

• otherwise (if char is signed):

    CHAR_MIN	          SCHAR_MIN
    CHAR_MAX	          SCHAR_MAX
  

Real numbers

• float, double and long double have the same relation to each other that the integer short, int and long types have
  • double is usually the most efficient real number representation
  • float is smaller than or the same size as double
  • long double (which is an ANSI C invention) is larger than or the same size as double
• due to rounding problems, it's generally true that (a / b) * b will almost never yield the original value of a
• Example declarations:
  • float f
  • double dbl
  • long double huge

<float.h>

• machine dependent characteristics for the float and double types are defined in the <float.h> file