Syntax and Semantics, and the Program Development ProcessROBERT 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.

p

Variable Identifier myChar (memory location 1101010011)

Variable (char)

ValueData Type

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.