Lesson 3.2 data types for memory location

Introduction to Programming in C++
Eight Edition
Lesson 3.2:
Data types for memory
location

An Introduction to Programming with C++, Eight Edition
• Memory locations come in different types and sizes
• Type and size you choose depends on the item you want
to store
• A memory location will only accept an item that matches
its data type
• Data type of a memory location is determined by the
programmer when declaring the location
Selecting a Data Type for a Memory
Location
2

• Fundamental data types are basic data types built into
C++
– Also called primitive or built-in data types
– Include short, int, float, double, bool, and char
• bool data type stores Boolean values (true and false)
• short and int types store integers (numbers without a
decimal place)
– Differences are range of values and memory used (int
has the greater of both)
Location (cont’d.)
3

• float and double types store real numbers (numbers
with a decimal place)
– Differences are range of values, precision, and memory
used (double has the greater of each)
• char type stores characters (letter, symbol, or number
that will not be used in a calculation)
– Only one character stored at a time
• string data type is a user-defined data type (defined with
a class, or group of instructions)
– Can store zero or more characters
4

5

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• Numbers represented in internal memory using binary
(base 2) number system (two digits, 0 and 1)
• We are used to the decimal (base 10) number system
(ten digits, 0 through 9)
• Character data is stored using ASCII codes
– Eight-bit codes (bit = binary digit, 0 or 1)
– Upper- and lowercase versions of letters have distinct
codes
• Computer distinguishes between numbers and ASCII
codes based on data type
How Data Is Stored in Internal Memory
7

How Data Is Stored in Internal Memory (cont’d.)
8

How Data Is Stored in Internal Memory (cont’d.)
9

How Data Is Stored in Internal
Memory (cont’d.)
10

• Setting an initial value for a variable or named constant
is called initializing
• Required for constants; recommended for variables
• Memory locations are usually initialized with a literal
constant (item of data that can appear in a program
instruction and be stored in memory)
• Data type of literal constant should match data type of
memory location it is assigned to
Selecting an Initial Value for a
Memory Location
11

• Numeric literal constants initialize short, int, float, and
double data types
– Can contain digits 0 through 9, +, -, ., and e or E
(for scientific notation)
• Character literal constants initialize char data types
– Consist of one character in single quotation
marks
• String literal constants initialize string data types
– Zero or more characters enclosed in double
quotation marks
– Empty string (“”) is a valid string literal constant
Memory Location (cont’d.)
12

• Before assigning initial value to a memory location,
computer checks that value’s data type matches
location’s data type
• If they don’t match, computer performs implicit type
conversion to match them
– If initial value is converted to type that holds
larger numbers, value is promoted
– If initial value is converted to type that only holds
smaller numbers, value is demoted
• Promoting will not usually have adverse effects, but
demoting can (information is lost)
13

• Important to initialize memory locations with values of
the same data type
• Named constants should be initialized with the value
they will hold for the duration of the program
• Variables whose initial values are not known should still
be initialized
– short and int types usually initialized to 0
– float and double types usually initialized to 0.0
– string types usually initialized to empty string (“”)
– bool types initialized to either true or false
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• Variables and named constants are declared using a
statement (C++ instruction)
• A statement that declares a variable causes the
computer to set aside a memory location with the given
name, data type, and initial value
• Statements must follow correct syntax (rules of a
programming language)
• In C++, all statements must end with a semicolon
Declaring a Memory Location
16

When declaring variables, a data type and name must be
provided
• Syntax for declaring a variable in C++
– dataType variableName [= initialValue];
• After variable is declared, you use its name to refer to it
later in the program
• Initial value is optional but recommended
• If variable is not initialized, it contains the previous value
of that memory location, which may be the wrong type
(called a garbage value)
(cont’d.)
17

• Syntax for declaring a named constant in C++ – const
dataType constantName = value; • The const keyword
indicates that the memory location is a named constant
(value cannot be changed during runtime) • Initial value
required for constants, unlike variables • As with
variables, after declaring a constant, you can use its name
to refer to it later in the program
(cont’d.)
18

• Several advantages to using named constants when
appropriate
– Make program more self-documenting (meaningful
words in place of numbers)
– Value cannot be inadvertently changed during runtime
– Typing a name is less error-prone than a long number
– Mistyping a constant’s name will trigger a compiler
error; mistyping a number will not
– If the constant needs to be changed when modifying the
program, it only needs to be changed in one place
(cont’d.)
19

(cont’d.)
20

(cont’d.)
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(cont’d.)
22

The End ♥ ♥ ♥
26

Lesson 3.2 data types for memory location

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