Variables

-a variable is a named memory location which stores a value

--to use a variable in a program, it must be defined by giving it a type and identifier

eg: double Radius

Once defined the variable must be given a value

eg: Radius = 12.3 ;
the = sign is similar to the := in Pascal which means that the value is assigned to the variable

Using Named Constants

-defined in a statement and begins with the word "const"

--this is used to define a constant: in math Pi is a constant value (3.14159)...to represent this in C++, you do the following:

const double PI = 3.14 ;

--a constant is used to represent a value that does not change during the execution of a program

Choosing Identifiers

Rules for choosing identifiers:

must start with a letter
must contain only letters, digits and the underscore ( _ ) character
can be of any length
are case sensitive: Radius is different than radius

Built in Data Types

1. double

used to store positive or negative real numbers (decimals)
floating point numbers (decimals)
when the number is very large, it will be stored in scientific notation: the computer stores 1.23457 x 10⁸as 1.23457e+08
the double value is rounded to six digits

2. int and long

used to store positive and negative integers (no decimals!)
only difference is the range of values : long goes beyond 32767

3. char:

used to store a single character
can be used to store a single letter, digit or symbol like the % sign
requires single quotation marks:

Example: char Ch:

Ch = 'A';

cout<<Ch<<endl;

displays : A

VARIABLE DEFINITIONS

VARIABLES can be defined in single statements or in multiple variables in one line

example: int x,y,z

Char ch1,ch2

Expressions and Operators

-built in arithmetic operations include: (*) multiplication,

(+) addition, (-) subtraction, and ( / ) division

Promotion: numeric values of various types can be mixed in an expression: an expression involving two doubles, results in a double, however, whenever an integer and a double are used, C++ promotes the value with the narrow range to the value with the wider range: integer becomes a double: this avoids the problem known in Pascal as "type mismatch"

Integer Division: if you divide two integers, the resulting number will be truncated, or the decimals will be cut off!

Type Casting: when real division is done, type casting converts one of the values into a real number

Modulus Division: represented by %, Modulus division returns the remainder....similar to MOD in Pascal

Operator Precedence: same as order of operations in mathematics

Output Formatting

use width ( ) to control your output: creates a field width, so width(10) will allow 10 digits
use setf( ) to change the alignment (see handout)
use precision ( ) to specify the number of decimals

Defining Variables and Type Casting: More Details