Numeric Variable Types

C provides several different types of numeric variables. You need different types of variables because different numeric values have varying memory storage requirements and differ in the ease with which certain mathematical operations can be performed on them. Small integers (for example, 1, 199, and -8) require less memory to store, and your computer can perform mathematical operations (addition, multiplication, and so on) with such numbers very quickly. In contrast, large integers and floating-point values (123,000,000 or 0.000000871256, for example) require more storage space and more time for mathematical operations. By using the appropriate variable types, you ensure that your program runs as efficiently as possible.
C's numeric variables fall into the following two main categories:

• Integer variables hold values that have no fractional part (that is, whole numbers only). Integer variables come in two flavors: signed integer variables can hold positive or negative values, whereas unsigned integer variables can hold only positive values (and 0).
• Floating-point variables hold values that have a fractional part (that is, real numbers).

Within each of these categories are two or more specific variable types. These are summarized in Table 3.2, which also shows the amount of memory, in bytes, required to hold a single variable of each type when you use a microcomputer with 16-bit architecture.

Table 3.2. C's numeric data types.

Variable Type	Keyword	Bytes Required	Range
Character	char	1	-128 to 127
Integer	int	2	-32768 to 32767
Short integer	short	2	-32768 to 32767
Long integer	long	4	-2,147,483,648 to 2,147,438,647
Unsigned character	unsigned char	1	0 to 255
Unsigned integer	unsigned int	2	0 to 65535
Unsigned short integer	unsigned short	2	0 to 65535
Unsigned long integer	unsigned long	4	0 to 4,294,967,295
Single-precision	float	4	1.2E-38 to
floating-point			3.4E381
Double-precision	double	8	2.2E-308 to
floating-point			1.8E3082
1Approximate range; precision = 7 digits.
2Approximate range; precision = 19 digits.

Approximate range means the highest and lowest values a given variable can hold. (Space limitations prohibit listing exact ranges for the values of these variables.) Precision means the accuracy with which the variable is stored. (For example, if you evaluate 1/3, the answer is 0.33333... with 3s going to infinity. A variable with a precision of 7 stores seven 3s.)
Looking at Table 3.2, you might notice that the variable types int and short are identical. Why are two different types necessary? The int and short variable types are indeed identical on 16-bit IBM PC-compatible systems, but they might be different on other types of hardware. On a VAX system, a short and an int aren't the same size. Instead, a short is 2 bytes, whereas an int is 4. Remember that C is a flexible, portable language, so it provides different keywords for the two types. If you're working on a PC, you can use int and short interchangeably.