Operands and Operators

1
Operands and Operators

• data types
• operators

2
Basic Data Types

• char used to declare variables for storing
  character (textual) data, e.g. A
• int used to declare variables that store integer
  values, e.g. 100
• float used to declare variables that store real
  (floating point) values, e.g. 0.12345
• double used to declare variables that store
  double precision values, e.g 3.1415926536
• Quantifiers such as long, short, signed and
  unsigned could be applied to these basic data
  types
• Complex data types include enumerations, arrays,
  structures, unions, lists, stacks, queues, trees
• Pointers are a special data type that can hold a
  memory address

3
Data

• Variables
• global variables
• include ltstdio.hgt
• int num100 / declaration of global
  variable /
• int main()
• printf("Global value is d", num)
• return 0

• local variables
• include ltstdio.hgt
• int num100 / declaration of global
  variable /
• int main()
• int num10 / declaration of local variable /
• printf(Local value is d", num)
• return 0

4
Data

• attributes of Variables or identifiers
• name
• type
• size
• value
• other attributes include storage class, storage
  duration, scope and linkage

int total int total 0
5
Data

• Constants are declared using const keyword

include ltstdio.hgt main()
const float PI 3.141593 int
diameter float radius, circ, area printf("\nE
nter the diameter of a ") printf(" circle in
mm ") scanf("d", diameter) circ
(float) PI diameter radius (float) diameter
/ 2 area (float) PI (radius
radius) printf("\tIts circumference is .2f
mm\n", circ) printf("\tAnd its area is .2f
sq.mm\n ", area) return 0
Symbolic Constants are defined in the
preprocessor area of the program They are
declared using define CONSTANT_NAME Value
6
Operators

• Arithmetic Operators
• Assignment
• Addition
• Subtraction -
• Multiplication
• Division /
• Modulus
• Parenthesis () is used as in algebra
• variable expression

• Relational or comparison operators
• gt gt greater than
• lt lt less than
• gt greater than or equal to
• lt lesser than or equal to
• if (condition)
• statement
• Equality Operators
• equivalent
• ? ! not equal

7
Operators

• Logical Operators
• AND
• OR
• ! NOT
• if (condition1 AND condition2)
• statement
• Unary Operators
• unary minus
• sizeof(data_type)
• (type) variable_name

• Increment
• Decrement Operators
• i i 1 is equivalent to i
• i i - 1 is equivalent to --i
• prefix form variable is changed before
  expression is evaluated
• i --i
• postfix form variable is changed after
  expression is evaluated
• i i--

8
Rules

• Precedence
• order of evaluation

• Associativity
• direction of evaluation

Precedence
9
L-Value R-Value

• L-values
• Expressions that can appear on left side of
  equation
• Can be changed (i.e., variables)
• e.g. x 4
• R-values
• Only appear on right side of equation
• Constants, such as numbers (i.e. cannot write 4
  x)
• L-values can be used as R-values, but NOT vice
  versa

10
Confusing Equality () and Assignment ()
Operators

• Example
• if ( payCode 4 )
• printf ("You get a bonus!\n)
• If paycode is 4, bonus given
• If was replaced with
• if ( payCode 4 ) printf ("You get a
  bonus!\n)
• Paycode set to 4 (no matter what it was before)
• Statement is true (since 4 is non-zero)
• Bonus given in every case

11
Operators - demo
Output Addition 9 Division 0 Modulus
4 Postfix increment 4 Now a is 5 Prefix
increment 6 Now a is 6 Postfix decrement 5
Now b is 4 Prefix decrement 3 Now b is 3

• include ltstdio.hgt
• int main ()
• int a4, b5, result
• result a b
• printf("Addition d\n", result)
• result a / b
• printf("Division d\n", result)
• result a b
• printf("Modulus d\t\n", result)
• printf("Postfix increment d\n", a)
  printf("Now a is d\n", a)
• printf("Prefix increment d\n", a)
  printf("Now a is d\n", a)
• printf("Postfix decrement d\n", b--)
  printf("Now b is d\n", b)
• printf("Prefix decrement d\n", --b)
  printf("Now b is d\n", b)
• return 0

12
Type Conversion

• C allows for conversions between the basic types,
  implicitly or explicitly
• Explicit conversion uses the cast operator

• Example 2
• int i
• short int j1000
• ijj / wrong!!! /
• i(int)j (int)j / correct /

Example 1 int x10 float y,z3.14 y(float) x
/ y10.0 / x(int) z / x3
/ x(int) (-z) / x-3 -- rounded
approaching zero /
13
Implicit Conversion

• If the compiler expects one type at a position,
  but another type is provided, then implicit
  conversion occurs.
• Conversion during assignments
• char c'a'
• int i
• ic / i is assigned by the ascii of a /
• Arithmetic conversion if two operands of a
  binary operator are not the same type, implicit
  conversion occurs
• int i5 , j1
• float x1.0 , y
• y x / i / y 1.0 / 5.0 /
• y j / i / y 1 / 5 so y 0 /
• y (float) j / i / y 1.0 / 5 /
• / The cast operator has a higher precedence /

14
C Promotion Rules

• The C compiler uses the following diagram to
  promote the types if two operands do not agree in
  expressions

long double
double
float
unsigned long int
long int
unsigned int
int
char