Transcript Data Types and Sizes : (Continued)

ITEC113Algorithms and
Programming Techniques
C programming: Variables,
Expressions Part I
Objectives
• To understand what variables are
– initialization/garbage values
– naming conventions
• To learn about the frequently used data types
• To understand the components of
– an assignment Statements
– arithmetic expressions
• To learn about
– frequently used operators,
– operator precedence
VARIABLES
• Variables are basic data objects manipulated in a
program.
• Each variable has to be declared before use.
• Each variable has a name and a data type.
• You can give initial value (variable initialization) on
variable declaration.
Examples:
int x;
float sum=0;
char gender;
char name[10];
float avg;
int *fp;
VARIABLES
• Variable declaration allocates a cell in the main
memory whose size is determined by the data type
– For example for int 4 bytes are used, for double 8 bytes
are used
• When the variable is created in the main memory it
contains garbage value
– This is due to the existence of 1’s and 0’s in the memory. 1
means high voltage, 0 means low voltage.
• It is a good idea to initialize variables before first usage.
• A variable name is the symbolic representation of the
memory location that is allocated on variable
declaration
Rules on Variable Names:
• DO NOT use reserved words as variable names
(e.g. if, else, int, float, case, for, …).
• The first character has to be a letter or
underscore. It can not be a numeric digit.
The second and the other characters of the name can be any letter,
any number, or an underscore “_”.
Examples
Some valid names:
my_name, m113_1, salary, bluemoon , _at
Some invalid names:
my name, my-name , 1stmonth , salary! , guns&roses ,
Tradition on Variable Names:
These are NOT rules but you can increase the
quality of your program by using them!
• Select related and meaningful names
indicating tasks of the variables.
• Do not use variable names that exceed 8
characters.
• Use small case letters for variable names.
– Upper case letters are mostly used in the names
of symbolic constants.
Variable Declaration:
• Variable declaration is used to introduce the system to the variables
that the programmer decides to use on the rest of the program.
• On variable declaration,
– variable name,
– data type
are declared.
• Also you can give the initial value of the variable on its declaration.
Example :
int k ;
int m=15;
float fnumber= 1.75;
char ch=’w’ ;
Data Types of the Variables :
• A variable data type specifies:
– The kind of value a variable can store
– The set of operations that can be applied to the variable
• There are 3 main different data types and their derivations
for declaration in ANSI–C.
Main Data types Derived Data
Types
integer
short, long
float
Double
char
Data Types and Sizes : (Continued)
• Integers (int) :
• Integers are all numeric values that have no fractional or decimal
components.
• Integer numbers may be positive or negative.
Examples :
13
7
–6
208
1024
• C compiler allocates 4 bytes (32 bits) to an integer (int) variable.
• An integer variable can store values in the range
•
–32,768 through 32,767
• Derived Integers :
• short, long and unsigned are data types derived from int, and used to
keep integer values.
• The sizes of long and short is differentiated from int.
• The data type unsigned is used only with positive integers.
Data Types and Sizes : (Continued)
•The sizes of long and short is differentiated from int.
• The data type unsigned is used only with positive integers.
Data Types
Bytes Used
int
4 Bytes
short
2 Bytes
double
8 Bytes
unsigned
4 Bytes
Data Types and Sizes : (Continued)
Real Numbers :
• C compiler uses float and double data types for storing
real numbers.
• The float data type requires 4 bytes and has a precision of
seven digits
– This means after the decimal point you can have seven digits
Example:
3.14159
534.322344
0.3333333
0.1234567
• The double data type requires 8 bytes and has a precision
of fifteen digits
Example :
-3738.7878787878
3.141592653589790
0.123456789123456
Data Types and Sizes : (Continued)
• We can use Scientific Notation to represent real
numbers that are very large or very small in
value.
• The letters e or E is used to represent times 10
to the power.
Example:
• 1.23 x 10 5 is represented in C as 1.23e5 or 1.23e+5 or
1.23E5
• 1 x 10 -9 is represented in C as 1e-9
Data Types and Sizes : (Continued)
Character : ( char )
• Characters constants are usually used enclosed
single quotes
Example: ‘A’ , ‘7’,
• Only one byte of memory location is used by a
character variable.
• In ASCII code is used to represent uniquely any
one of the available 255 characters
Example:
A is represented by decimal 65 or
8-bit binary 0 1 0 0 0 0 0 1
Data Types and Sizes : (Continued)
Categories of characters :
• Alphabetic Letters :
– ( Upper case : ‘A’ , ‘B’, …….. ‘Z’ )
– ( Lower case : ‘a’ , ‘b’, …….. ‘z’ )
• Numeric digits
– ( ‘1’,’2’,’3’,…………,’9’,’0’ )
• Special Characters
– ( blank, ‘+’,’#’,’-‘,’_’,……..)
• Control Characters
– ( ‘\n’ , ‘\t’ , ……. )
Assignment Statements
• The ‘=‘ sign is an assignment operator.
• Assignment statements replace old values of the
variables with the new ones
• An assignment statement assigns a value or a
computational result to a variable.
Example
stores values 1 and 0 to cnt and sum.
cnt = 1; sum = 0;
stores character ‘Y’ to ch
ch = ‘Y’;
sum = sum + 1; avg = sum / cnt;
stores computational results to sum and avg
Expressions
• Arithmetic Expressions involve arithmetic
operators such as *,+,-,/,%:
– Example : a * 5 + b % 4
• Relational Expressions involve relational
operators that compare two values such as >,<,==
etc:
– Example:
a > b
• Logical Expressions involve the logical and and
or operators && and || and are used to combine
relational expressions:
– Example: ( a > b && c == 7 )
Arithmetic Expressions
In the Assignment Statement:
M = a*5+ b%4 ;
• The expression to the right of the assignment operator
( = ) involves an arithmetic operation that combines
arithmetic operands with arithmetic operators.
• The most commonly used arithmetic operators are:
–
–
–
–
–
Addition (+) Operator
Subtraction (-) Operator
multiplication (*) Operator
division (/) Operator
remainder (%) Operator
For real or integer
numbers
For integer numbers only
Operator Precedence Rules
• Arithmetic expressions inside parentheses are
executed first (left to right).
• Unary operators ( minus signs and plus signs)
are executed before multiplications, divisions
and remainder operations.
• Additions and subtractions are executed last.
parentheses
-ve and +ve
signs
Mult. Div., and
mod.
Add and
subtract
Operators
( ,)
+ , - ( unary )
*,/, %
+ , -
Associativity
Left to Right
Right to Left
Left to Right
Left to Right
Priority Level
Highest
Lowest
Operator Precedence Rules:Examples
•
? =3 + 5* 4
– Evaluated as 3 + (5*4)
•
? = 8 / (5 – 2)
– Evaluated as
•
8 + (12%5)
and the result is 10
( (6*5) /2) + 2 and the result is 17
?=9–4+2*6
– Evaluated as 9 –
•
and the result is 2
?=6*5/2+2
– Evaluated as
•
8 /3
? = 8 + 12 % 5
– Evaluated as
•
and the result is 23
4 + (2*6) and the result is 17
? = 1 + 2 * (3 + 4)
– Evaluated as 1 + (2 * (3+4)) and the result is 15
•
?=5*2+9%4
– Evaluated as
•
(5*2) + (9 % 4) and the result is 11
? = 5 * 2 % ( 7 – 4)
– Evaluated as
(5 * 2) % (7 – 4) and the result is 1
THAT’S IT FOR NOW!
NEXT LECTURE: MORE ON VARIABLES, DATA TYPES
AND EXPRESSIONS