Operators in C

Balochistan University of IT & MS 1
Lecture 4
Operators and Expressions
CS1
Introduction to Programming
Methodologies & Abstraction
Fall 2005
Balochistan University
of I.T & M.S
Faculty of System Sciences
Sadique Ahmed Bugti

Expressions
• Expressions are meaningful combinations
of constants, variables and function calls.
• Most expressions have both a value and a
type.
• The expression may consist of a single
entity, such as a constant or variable, or it
may consist of some combination of such
entities, interconnected by one or more
operators.
• Expressions can also represent logical
conditions which are either true or false.

Example Expressions
• Several simple expressions are given below:
a + b
– This expression represents the sum of the
values assigned to variables a and b.
x = y
– This expression causes the value
represented by y to be assigned to x.

Example Expressions
t = u + v
– In this expression, the value of the
expression (u + v) is assigned to t.
It is poor programming practice to mix
data types in assignment expressions.
Thus, the data types of the constants or
variables on either side of the = sign
should always match.

Expression Statements
• An expression statement consists of an
expression followed by a semicolon.
• For example:
area = PI * radius * radius;
– This causes the value of the
expression on the right of the equal
sign to be assigned to the variable on
the left.

Assignment Statements
• In an assignment statement, the value
of a variable is replaced with the value
of an expression.
• e.g. PI = 3.14159;
• The general form of the assignment
statement is:
variable = expression;
• The = operator is used for assignment.

Assignment Statements
• Even though assignment statements sometimes
resemble mathematical equations, the two
notions are distinct and should not be confused.
• The mathematical equation:
χ + 2 = 0
does not become an assignment statement
when you type:
x + 2 = 0;
• The left side of the equal sign is an expression,
not a variable, and this expression may not be
assigned a value.

Defining Equations
• The following example is the equation
of a straight line:
Algebra: y = mx + c
C: y = m * x + c
Algebra: a = πr2
C: area = π * r * r

Defining Equations
X1 = (-b+ sqrt((b * b) – 4 * a * c )) )/ (2 *a)
X2 = (-b – sqrt((b * b) – 4 * a * c))) / (2 * a)

What are operators?
• C has a rich set of operators (i.e., things like +
- * / ), which allow you to write complicated
expressions quite compactly.
• General expressions are formed by joining
together constants and variables (operands)
via various operators.
• Operators in C fall into a number of classes:
– arithmetic operators, unary operators,
relational and logical operators, assignment
operators,equality operators, and the
conditional operator.

Unary Operators
• Unary operators are operators that only
take one argument.
+123 positive 123
-123 negative 123
!i logical negation (i.e., 1 if i is zero, 0 otherwise)
++i adds one to i, and returns the new value of i
– –i subtracts one from i, and returns the new value of i
i++ adds one to i, and returns the old value of i
i– – subtracts one from i, and returns the old value of i

Unary –
• The most common unary operator is the
unary minus, which occurs when a
numerical constant, variable, or
expression is preceded by a minus sign.
• Note that the unary minus is distinctly
different from the arithmetic operator (–)
which denotes subtraction, since the latter
operator acts on two separate operands.
e.g. -12

Binary Operators
• Binary operators work on two
operands ('binary‘ here means 2
operands, not in the sense of base-2
arithmetic).

Binary Operators
+ addition
– subtraction
* multiplication
/ division
% remainder (e.g., 2%3 is 2), also called 'modulo'
<< left-shift (e.g., i<<j is i shifted to the left by j bits)
>> right-shift
& bit wise AND
| bit wise OR
^ bit wise exclusive-OR

Binary Operators
&& logical AND (returns 1 if both operands are
non-zero; else 0)
|| logical OR (returns 1 if either operand is non-
zero; else 0)
< less than (e.g., i<j returns 1 if i is less than j)
> greater than
<= less than or equal
>= greater than or equal
== equals
!= does not equal
? conditional operator

Assignment Operators
• The most common assignment
operator in C is the equals operator, =.
– It is used to change the value of a variable.
• For instance, the expression:
f = 3.4;
• causes the floating-point value 3.4 to
be assigned to the variable f.

• Multiple assignments are permissible in
C. For example,
i = j = k = 4;
• causes the integer value 4 to be
assigned to i, j, and k, simultaneously.

• Assignment operators are really just binary
operators.
= assignment
+= addition assignment
-= subtraction assignment
*= multiplication assignment
/= division assignment
%= remainder/modulus assignment
&= bit wise AND assignment
|= bit wise OR assignment
^= bit wise exclusive OR assignment
<<= left shift assignment
>>= right shift assignment

• Examples of using assignment
operators:
velocity = distance / time;
force = mass * acceleration;
count = count + 1;

Arithmetic Operators
• There are four main arithmetic operators in C:
addition +
subtraction –
multiplication *
division /
• There is no built-in exponentiation operator in
C . Instead, there is a library function (pow)
which carries out this operation.
e.g. x2 is represented as x * x

Division, /
• The division operator is special.
– There is a vast difference between an
integer divide and a floating-point divide
– In an integer divide, the result is truncated
i.e. the fractional part is discarded
– If either the divisor or the dividend is a
floating-point number, a floating-point
divide is performed.
– e.g. 19/10 = 1
– 19.0/10.0 = 1.9

Integer Division, /
• Integer division returns just the result
with no remainder.
• For example:
15/3 = 5 16/3 = 5 17/3 = 5
3/15 = 0 0/4 = 0 4/0 = undefined

Arithmetic Operators
Operation C Operator Algebraic
Expression
C Expression
Addition + f + 7 f + 7
Subtraction – a – b a - b
Multiplication * bm b * m
Division / x / y or x ÷ y x / y
Modulus % r mod s r % s

Parentheses, ( )
• Parentheses are used as punctuators
to clarify or change the order in which
operations are performed.
• For example:
a = 12 * (x + y)

Note
• An alternative to turning one statement into two is to
split long statements into multiple lines.
– When breaking up a line, the preferred split point is where
the parenthetic nesting is lowest.
result = ( ( ( x + 1 ) * ( x + 1 )) - ( ( y + 1 ) * ( y + 1 ) ) );
1233333332223333333211123333333222333333321
• The best place to break the line is where the nesting
level is lowest; in this case at the – operator in the
middle:
result =(((x1 + 1) * (x1 + 1))
-((y1 + 1) * (y1 + 1)));

Operator Precedence
• The operators within C are grouped
hierarchically according to their precedence
(i.e., their order of evaluation).
• Amongst the arithmetic operators, * and /
have precedence over + and –.
– In other words, when evaluating
expressions, C performs multiplication
and division operations prior to addition
and subtraction operations.
• The rules of precedence can always be
bypassed by the use of parentheses, ( , ).

Operator Precedence
• For example:
a - b / c + d
is equivalent to the unambiguous
expression
a - (b / c) + d
• since division takes precedence over
addition and subtraction.

Operator Precedence and
Associatively
• The precedence of an operator gives the
order in which operators are applied in
expressions: the highest precedence
operator is applied first, followed by the next
highest, and so on.
• The associatively of an operator gives the
order in which expressions involving
operators of the same precedence are
evaluated.

Associatively

Associatively
• Note: the +, – and * operators appear twice
in the above table. The unary forms (on the
second line) have higher precedence that
the binary forms.
• Operators on the same line have the same
precedence, and are evaluated in the order
given by the associatively.
• To specify a different order of evaluation
you can use parentheses. In fact, it is often
good practice to use parentheses to guard
against making mistakes in difficult cases,
or to make your meaning clear.

Exercise
Evaluate the value of following expressions
m = 3, n=4
X = 2.5, y= 10
1. Z= m + n + x + y
2. Z= m + x * n + y
3. Z= X / y + m / n
4. Z= X – y * m + y / n
5. Z= X / 0

Mathematical Operators For
Increment / Decrement
k
k :=k+1
k 4
3 k 9
K:= k-1
k 8

Exercise
command x y z
x = 2 2 unknown unknown
x = x + 1 3 unknown unknown
y = 2 3 2 unknown
z = x + y 3 2 5
y = x + z 3 8 5
z = z - 2 3 8 3
x = 3 + z 6 8 3
x = y mod z 2 8 3

Relational Operators
Symbol Operator Example
< Less Than a Greater Than a > b
= Equal to a = b
<= Less or Equal a <= b
>= Greater or
Equal
a >=b
<> Not Equal a <> b

Relational Operators
a = 2, b=5
Symbol Operator OutPut
< a a > b 0
= a = b 0
<= a <= b 1
>= a >=b 0
<> a <> b 1

Logical Operators
Effects on relational expression’s results also AND, OR combines
two or more Relational expressions, Results will be returned
either TRUE( 1 ) or FALSE ( 0 ) regards with specific situations.
AND AND A d
OR OR a d
NOT NOT NOT ( a < b )

Logical Operators
a = 2, b = 5, c = 9, d = 7
AND a d 1
OR a d 1
NOT NOT ( a < b ) 0

Exercise
Before Execution Expression After execution
a = 2 , b = -1 a = a + b a=
a = 2 a = -a a=
x = 4 , y := 3 z = x > y + 1 z = , x =, y =
a = 1 z = a != a z =
x = 11, y = 6 z = x > 9 && y != 3 z =
x = 11, y = 6 z = x = 5 || y != 3 z =
x = 11, y = 6 z = ! ( x > 14 ) z=
x = 11, y = 6 z = !( x > 9 AND y !=23) z=
a = 13 , b = 4 z = a % b z=
a = 3, x = a z = x = a; z= , x= , a=

Operators in C

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Operators in C