Primitive Data Types

Integer Types

Three integer types:

• short
  • $2^{15}-1$
  • 2 Bytes
• int
  • Maximum at least $2^{15}-1$
  • At least 2 Bytes
  • Normally $2^{31}-1$
  • Normally 4 Bytes
• long
  • Maximum at least $2^{31}-1$
  • At least 4 Bytes

unsigned Keyword

Creates a new data type in which only nonnegative values are allowed. Can hold twice as many positive values:

• short, int $2^{15}-1(32767)\to 2^{16}-1(65535)$
• modern int, long $2^{31}-1\to 2^{32}-1$

Syntax:

unsigned short NAME;
unsigned int NAME;
unsigned NAME; // Equivalent to unsigned int

Different Representation

Bases:

• N base-10
• 0N base-8
• 0xN base-16

Suffix:

• NL Specify N's type is long
• NU Specify N is unsigned

Floating-point Types

Numbers that include a decimal fraction are called floating-point numbers, which are used to approximate real numbers in mathematics. Three floating-point types:

• float
• double
• long double

Representation

• 2.0
• 2.9979E+8 $2.9979\times {10}^8$
• 3.0E-2 $3.0\times {10}^{-2}$

Text Types

See Strings and Characters for details.

Boolean Type

Booleans are special integers

• Takes up 1 byte
• Value true or false (1 or 0)

*Enumeration Type

Enumeration types list the elements that constitute their domains.

Syntax:

enum NAME {ELEMENT_LIST};

• ELEMENT_LIST A list of identifiers called enumeration constants
• name The name of the new type

Using the newly created type:

NAME var;

• Declares var to be the type of NAME
• var can take on any of the values in the ELEMENT_LIST

Internal Representation

The values of an enumeration type are stored internally as integers. Unless given the initial index, the compiler ordinarily assigns consecutive integers to the enumeration constants, starting with the integer 0 (0, 1, 2, ...).

enum directionT { North, East, South, West };
// Now North = 0, East = 1, etc.

To control the encoding:

enum coinT {
  Penny = 1,
  Nickel = 5,
  Dime = 10,
  Quarter = 25,
  HalfDollar = 50
};

If the value of any enumeration constant is not specified, the compiler simply adds one to the value of the previous constant.

enum monthT {
  January = 1, February, March, April, May, June,
  July, August, September, October, November, December
};

// The same effect as
const int JANUARY = 1;
...

Benefits:

• Separate type name are more easily readable
• Variables of enum type cannot be assigned integer values without typecast, preventing range outage
• Easier to debug with names rather than just integers

Scalar Types

A data type that can represent a single value. In C++, enumeration types, characters and the various representation of integers are scalar types, and are converted into integers automatically as values.

Example:

string DirectionName(directionT dir) {
  switch (dir) {
    case North: return "North";
    case East:  return "East";
    case South: return "South";
    case West:  return "West";
    default:    Error("Illegal direction value");
  }
}

Pointers and Arrays

See Memory and Pointers and [[CS106B/Arrays]]