Data Types, Variables, Constants, and Identifiers

(BICS 265 Notes.1)

Learn how to maintain data in C++...

To process data, a program must have a place to store it and an identifier for referencing it.

Like other programming languages, C++ provides a method for declaring data areas used by a program. C++ also supports a variety of data types...

Standard C++ Data Types
char	A single alphabetic character, numeric digit, or punctuation symbol Examples y 7 $
int	A whole number (with no decimal places) Examples 231 -15
float	A real number (with decimal places) Examples 7.304 -5.716E25

While some languages provide a string data type for storing words or phrases (such as a customer name or street address), C++ has no string data type...

Strings in C++

Represented by an array of characters

Each letter or digit in the word or phrase occupies an adjacent character location

Example

An array of characters

While the standard data types are fairly simple, they have many variations.

The variations support different programming requirements on different kinds of computers...

Common Variations on Standard Data Types
signed char char	Default for character data One byte in size Each character has a decimal value from -128 to 127 Positive values support 7-bit ASCII code (128 characters) Examples y has a decimal value of 121 7 has a decimal value of 55 $ has a decimal value of 36
unsigned char	One byte in size Each character has a decimal value from 0 to 255 Expands on the ASCII character set (256 characters)
short int short	Two bytes in size on PCs Number may be from -32,768 to 32,767
unsigned short int unsigned short	Two bytes in size on PCs Number may be from 0 to 65,535
long int int long	Default for integer data Four bytes in size on PCs Number may be from 2,147,483,648 to 2,147,483,647
unsigned long int unsigned long unsigned	Four bytes in size on PCs Number may be from 0 to 4,294,967,295
float	Four bytes in size on PCs Always signed Number may be from -3.4E38 to 3.4E38 WARNING: Some significant digits may be truncated Example 1234567.89 would be stored as 1.23457E6
double	Eight bytes in size on PCs Always signed Number may be from -1.7E308 to 1.7E308 Stores twice as many significant digits as type float
"Select the proper data type based on the magnitude of the data to be stored..."

Every data area your program uses must be declared to the compiler. This is done by specifying its data type and identifier name. It is optional to provide an initial value...

Declaring Data Areas in C++

General syntax: datatype identifiername;

Where datatype is a valid data type (such as int, float, char, etc...) and identifiername consists of up to 32 alphanumeric characters or underscores with no embedded blanks. The first character of the identifier must not be a numeric digit.
The following are some valid identifier names:

Amount_Due
Total_for_1998
_1998_Sales
CustCreditLimit

Sample Data Declarations (uninitialized)

short int Number_of_Employees;
unsigned char KeyStroke;
float BalanceDue;
unsigned long int Really_Big_Number;
char Address[30];

Notes

[ ]

The value of an uninitialized data area is generally unpredictable when the program begins execution.

Sample Data Declarations (initialized)

unsigned short int Count = 0;

char Again = 'Y';

float TotalSales = 3127.94;

float TempF = -12.4;

char CustName[30] = "Jane Doe";

Notes

Enclose character values in single quotes (apostrophes).

Enclose string values within double quotes.

It is possible to declare multiple data areas of the same type in a single statement...

Declaring Multiple Data Areas of the Same Type

List identifiers after data type

Individual data areas may be initialized

Examples

float Length, Width;

int X = 3, Y = -5 , Z;

char TransCode = '1',

KeyValue;

"Because the compiler ignores spaces, tabs, and returns (whitespace characters), you can continue a C++ statement on the next line (after indenting for clarity)."

Not all data changes during program execution. For example, if a program calculates the area of several circles based on their radius (PI times the square of the radius), the value of PI would never change.

Unlike most programming languages, C++ differentiates between constants and variables...

Declaring Constants in C++

Code const before data type

Compiler will flag statements that attempt to modify the value of the data area

Examples

const char Yes = 'Y';

const float PI = 3.14156;

"Data areas that are not constant are automatically variable..."

Sample Program

Programming Exercise