Variables, Values,
and Types:
MEMORY:
MEMORY:
Memory is a collection of locations called variables
In a programming language, we get at the location by using a variable
Each variable has
A name (an identifier)
A type (the kind of information it can
contain)VARIABLE:
§Refer to memory location where a particular value is
stored
§Type of data decides the amount of memory allocated to variables
§Names assigned to variables to store a particular data,
help us in retrieving the data as and when required
MEMOMY AND VARIABLE:
Memory is a collection of locations
called variables
In a programming language, we get at
the location by using a variable
Each variable has
A name (an identifier)
A type (the kind of information it can
contain)
Basic types include
int (integers – whole numbers: 17, -42)
double (floating-point numbers with optional
fraction and/or exponent: 3.14159, 6.02e23)
char (character data: ‘a’, ‘?’, ‘N’, ‘ ’,
‘9’)
Note: ‘9’ is a character; 9 is an
integer – they are different and have different types
DECLARING VARIABLE:
int months;
Integer variables
represent whole numbers:
1, 17, -32, 0 Not 1.5, 2.0, ‘A’
double pi;
Floating point
variables represent real numbers:
3.14, -27.5, 6.02e23,
5.0 Not 3
char first_initial, middle_initial, marital_status;
Character variables
represent individual keyboard
characters:
'a', 'b', 'M', '0' ,
'9' , '#' , ' ' Not "Bill"
DATA TYPE:
§Decides the amount of memory to be allocated to a
variable to store a particular type of data
§Declaring a variable
úAllocates memory
úPortion of memory is referred to by the variable name
§General form of declaring a variable
údata
type (variable name)
§Common data types
- úNumeric
- Alphanumeric
§Type int
úStores numeric data
úConsists of a sequence of one or more digits
úIncludes only whole numbers
§Type char
úStores a single character
úThe single character is enclosed within two single
quotation marks
úDigits can also be stored as characters but cannot be
used for calculations
TYPE float:
úStores values containing decimal places
úStores either whole or fractional numbers
§Type double
úStores twice the
number of digits than a float type
úOccupies double
memory space than a float
§Precise number of digits stored by float
and double types depends upon the particular computer system.
Guidelines for
specifying Variable Names:
§Must begin with an alphabet
§First character to be followed by a sequence of letters
or digits or special character ‘underscore’
§Avoid using letter O in situations where it can be
confused with the number 0 and the lowercase letter l can be mistaken with the
number 1
§Uppercase and lowercase letters are treated different
§Name of the variable should be descriptive of the value
it holds
RESERVED WORDS:
Certain identifiers have a
"reserved" (permanent, special) meaning in C#
•We’ve seen int already
•Will see a couple
of dozen more eventually
These words always have that special
meaning, and cannot be used for other
purposes.
•Cannot be used
names of variables
•Must be spelled
exactly right
•Sometimes also
called “keywords”
PROGRAM EXECUTION:
A memory location is reserved by declaring a C# variable
You should give the variable a name that helps someone else reading the
program understand what it is used for in that program
Once all variables have been assigned memory locations, program
execution begins
The CPU executes instructions one at a time, in order of their
appearance in the program
AN EXAMPLE:
/* calculate and print area of 10x3 rectangle */
void Main(string [] args)
{
int rectangleLength;
int rectangleWidth;
int rectangleArea;
rectangleLength = 10;
rectangleWidth = 3;
rectangleArea = rectangleLength * rectangleWidth ;
Console.WriteLine(“with length {0} and width {1} the area of rectangle is {2}”, rectangleLength,
rectangleWidth ,rectangleArea);
CONVERT CLASS:
§Converts a base data type to another base data type.
§Common methods
úConvert.ToInt16
úConvert.ToInt32
úConvert.ToDouble
úConvert.ToBoolean
úConvert.ToChar
úConvert.ToDateTime
/////////////////////////////////////END OF SESSION/////////////////////////////////////////////////
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