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.