Syntax and Semantics,
and the Program
Development Process
ROBERT REAVES
Four Basic Control Structures?
Sequence
Selection (branch)
Looping (repetition)
Subprogram (function)
Program
Main function
Square function
Cube function
C++ Program Structure
Every C++ program must have a function named main.
Always begins with the first statement of main.
The body of a function is the statements between the ({) and (}).
Master(main) -> Servants(functions)
Value-Returning Functions
Square and Cube are both value-returning functions.
Returns a single value to it’s caller.
How do we know what the function returns?
Who calls main?
Main Function
Required function.
Execution begins here.
Returns a value to the OS.
Syntax and Semantics
Programming language is a set of rules, symbols, and special words
used to construct a program.
Syntax is formal rules governing how valid instructions are written in a
programming language.
Semantics is the set of rules that determines the meaning of
instructions written in a programming language.
Metalanguage is a language that is used to write syntax rules for
another language.
Syntax Templates
Identifier is a name associated with a function or data object and
used to refer to that function or data object.
Made up of letters (A-Z, a-z), digits (0-9), and or the underscore
character (_).
Must being with a letter or underscore.
Identifiers (valid)
sum_of_squares
J9
Box_22A
Bin3D4
count
Identifiers (invalid)
40Hours
Get Data
box-22
cost_in_$
int
Reserved Words
Reserved word is a word that has special meaning in C++; it cannot
be used as a programmer-defined identifier.
Example:
int
char
return
for
const
Data Types
Data type a specific set of data values, along with a set of
operations on those values.
Each piece of data must be a specific data type.
Determines how the data is represented in the computer and the
kinds of processing the computer can perform on it.
Can define your own data types. (programmer-defined types)
Char Data Type
char describes data consisting of one alphanumeric character.
(letter, digit, or special symbol)
Example:
‘A’
‘1’
‘&’
Each character must be enclosed in single quotes.
String Data Type
String is a sequence of characters, such as a word, name, or
sentence, enclosed in double quotes.
Example:
“Hello, World!”
“Robert”
“Today is going to be a LONG class. =)”
What is a string containing no characters?
Not supplied by the C++ standard library.
Declarations
Identifiers can be used to name both constants and variables.
How do we tell the computer what an identifier represents?
Declaration a statement that associates an identifier with a data
object, a function, or a data type so that the programmer can refer
to that item by name.
Example:
int year;
Data Objects
Constants and variables collectively are called data objects.
Variables
A program operates on data, which is stored in memory.
Variable a location in memory referenced by an identifier, that
contains a data value that can be changed.
Symbolic name associated with memory location is the variable
name or variable identifier.
Declaring a variable means specifying both the variable’s name
and its data type.
Variable Identifier myChar (memory location 1101010011)
Variable
p
(char)
Data Type
Value
Constants
Constant is something whose value never changes.
Literal value any constant value written in a program.
Named Constant (symbolic constant) a location in memory,
referenced by an identifier, that contains a data value that cannot
be changed.
const DataType Identifier = LiteralValue;
Executable Statements
Assignment statement a statement that stores the value of an
expression into a variable.
Expression an arrangement of identifiers, literals, and operators that can
be evaluated to compute a value of a given type.
lastName = “Reaves”;
(=) what does the meaning of this operator mean?
String Expressions
Can’t perform arithmetic on strings, however you can use the (+)
operator to perform something called concatenation.
Result of concatenating two strings is a new string containing the
characters from both strings.
Output
Can write out values or variables and expressions by using a special
variable named cout along with the insertion operator (<<).
Displays on the standard output device, usually the display screen.
Cout is predefined in C++ systems to denote an output stream.
What is we want (“) is our output?
How do we terminate an output line?
Comments
Denoted by (//) or (/* */)
Single line or block comments
Ignored by the compiler
Can appear anywhere but in the middle of an identifier, a reserved
word, or a literal constant.
You must use them or your coworkers and classmates will develop a
seething hatred for you.
Failure to use proper comments is grounds for execution.
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