Constants And Internal Representation
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ANSI C acknowledges that the size and numeric range of the basic data types (and their various permutations) are implementationspecific and usually derive from the architecture of the host computer. For Appmethod C++, the target platform is the IBM PC family (and compatibles), so the architecture of the Intel Pentium family of microprocessors governs the choices of internal representations for the various data types.
The following table lists the sizes and resulting ranges of the data types.
32bit data types, sizes, and ranges
Type 
Size (bits) 
Range 
Sample applications 
unsigned char 
8 

Small numbers and full PC character set 
char 
8 

Very small numbers and ASCII characters 
short int 
16 

Counting, small numbers, loop control 
unsigned int 
32 

Large numbers and loops 
int 
32 

Counting, small numbers, loop control 
unsigned long 
32 

Astronomical distances 
enum 
32 

Ordered sets of values 
long 
32 

Large numbers, populations 
float 
32 

Scientific (7digit precision) 
double 
64 

Scientific (15digit precision) 
long double 
80 

Financial (18digit precision) 
Internal Representation Of Numerical Types shows how these types are represented internally in the Intel Pentium family of microprocessors.
See Also
 Constants
 Integer Constants
 Floating Point Constants
 Character Constants
 The Three char Types
 Escape Sequences
 Widecharacter And Multicharacter Constants
 Unicode Character Types and Literals (C++0x)
 String Constants
 Enumeration Constants
 Internal Representation Of Numerical Types
 Constant Expressions
 Extended Integer Types: __int8, __int16, __int32, __int64