Download Operators and Expressions

CH/S4CIT(A)/Sept. 2005.
OPERATORS AND EXPRESSIONS
Operators

4 types of operators in Pascal:
i.
arithmetic operators
ii.
relational operators
iii.
logical operators
iv.
string operators
Arithmetic operators
operation
operator
operand type(s)
result type
example
positive unary
+
integer, real
same type
+x
positive numbers
negative unary
-
integer, real
same type
-x
negative numbers
addition
+
integer, real
same type
x+y
add y to x
subtraction
-
integer, real
same type
x-y
subtract to x
multiplication
*
integer, real
same type
x*y
multiply x by y
integer division
DIV
integer
integer
x DIV y
division
/
integer, real
real
x/y
integer modulo
MOD
integer
integer
x MOD y

quotient after integer division of x
by y
divide x by y
remainder after integer division of
x by y
e.g.
algebra expression
Pascal expression
x + 3y
x + 3 * y
x - y
z
x - y / z
xy
z
x * y / z
(x + y)
z
(x + y) / z
x(-y)
x * (-y)
z
xy

meaning
(ref.)
exp(exp(z*ln(y))*ln(x))
For integer powers
x3 : x*x*x
OPERATORS AND EXPRESSIONS
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CH/S4CIT(A)/Sept. 2005.

For real powers
xy : exp(y*ln(x)) which in mathematics notation e

y ln x
where e  2.718 and 1n means log e .
Sample statements:
Area := (Base * Altitude) / 2;
FirstRoot := (-B + exp(ln(B*B - 4*A*C)/2))/(2*A);
r := 123; s := 7;
t := r mod s; (*then t = 4*)
u := r div s; (*then u = 17*)
Relational Operators


Relational operators are used to compare two values. The result of comparison is either ‘True’ or ‘False’.
operator
operand type(s)
result type
example
meaning
=
any type but file
Boolean
x=y
<>
any type but file
Boolean
x<>y
x is not equal to y
>
any simple type
Boolean
x>y
x is greater than y
<
any simple type
Boolean
x<y
x is greater than y
>=
any simple type
Boolean
x>=y
x is greater than or equal to y
<=
any simple type
Boolean
x<=y
x is less than or equal to y
x is equal to y
e.g. if x = 3, y = 7.5, a = 120, b = 6
(x + 2*y ) < (a / b)
OPERATORS AND EXPRESSIONS
gives a
value
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CH/S4CIT(A)/Sept. 2005.
Logical operators

Logical operators are used in logical operations. They operate on Boolean data or expression and return
value of either “True” or “False”.

Three Logical Operators:


operator
operand type
result type
meaning
NOT
Boolean
Boolean
logical complement
AND
Boolean
Boolean
logical and
OR
Boolean
Boolean
logical or
Results of each operator (Truth Table)
x
y
NOT X
NOT y
x AND y
x OR y
T
T
F
F
T
T
T
F
F
T
F
T
F
T
T
F
F
T
F
F
T
T
F
F
e.g. if A = 3, B = 2, C = 1
NOT ((B*B - 4*A*C)) < 0
A > 2 OR A < 0
B < 10 AND B > 0
returns false
returns true
returns true
String Operators

Only one string operator: concatenation, i.e. ‘add’ two strings, the second string is added to the end of the
first string.

e.g. Str1 := 'Con' + 'cate' + 'nate';
Str1 is assigned ‘Concatenate’.

Strings may be compared using relational operators. String comparisons are performed by taking one
character at a time from the leftmost character of each string. The ASCII values of the characters from the
two strings are compared.
** ASCII - American Standard Code for Information Interchange.

All operation must be done with strict restriction on type.

Example:
If the variable declaration is as follows:
var
a, b
c, d
e
: integer;
: real;
: string;
Then the following statements are wrong in syntax:
a
e
c
c
:=
:=
:=
:=
c + b;
12 + 43;
e * 5;
a div b;
OPERATORS AND EXPRESSIONS
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CH/S4CIT(A)/Sept. 2005.
** Expression

An expression may be simply a constant, a variable, or a combination of constants, variables and functions
with operators.
e.g.

force * distance * cos(angle)
Only a single value can be returned from an expression no matter how complicated the expression is.
*** Order of Precedence of Operators

Operators in expression are evaluated in order of their precedence.

For operators of equal precedence, they will be evaluated as they are encountered, reading from left to right.
precedence
operators
operator class
( )
Parenthesis
2
NOT
Unary
3
*, /, DIV, MOD, AND
Multiplying
4
+, -, OR
Adding
=, <, >, < >, < =, > =, IN
Relational
1 (highest)
5 (lowest)
OPERATORS AND EXPRESSIONS
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