Transcript Part2
Data Types, Identifiers, and Expressions
Topics to cover here:
Data
types
Variables and Identifiers
Arithmetic and Logical Expressions
Programming Fundamental Slides
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Data Types
A data type provides a method of
modeling or representing a particular set
of values and determines what operations
can be performed on those values.
Programming Fundamental Slides
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Data Types in The Algorithmic Language
Predefined Data Types:
INT : values (e.g. 5 , -321 , 12)
operations (e.g. +, -, *, /, , MOD, <, >, =, ≠, ≤, ≥ )
FLOAT : values (e.g. 3.2 , 1.23E+5 , 0.34E-2)
operations (e.g. +, -, *, /, <, >, =, ≠, ≤, ≥)
BOOL : values (true , false)
operations (e.g. AND, OR, NOT)
CHAR : values (e.g. ‘A’ , ‘t’ , ‘(‘ , ‘5’ , ‘;’ )
operations (e.g. <, > , ≤, etc.)
String values (e.g. “ABC” , “computer”, “960”)
NOTE: In C++ language, some of the operations have
different symbols.
Programming Fundamental Slides
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Identifiers, Locations, and Variables
Memory:
It is a part of the computer
that has many locations (of fixed size)
used to store values (data) and
instructions.
Programming Fundamental Slides
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Identifiers, Locations, and Variables.. cont.
Identifiers (Names):
- Use meaningful identifiers (names) to represent
data in your program.
- Identifiers are used to refer to memory
locations: to store data in them or retrieve data
from them.
The rule of defining an identifier:
(1) It may contain
letters (A .. Z , a .. z ) ,
digits (0, 1, 2, …, 9), and
underscore ( _ ).
(2) It should begin with a letter.
Programming Fundamental Slides
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Identifiers, Locations, and Variables.. cont.
NOTES:
Some programming languages are case
sensitive. That is the uppercase identifiers are
different than lowercase identifiers (as in C++).
In
programming languages, some words cannot
be used as identifiers in your program. Such
words are called reserved words (or keywords)
that have special use.
Programming Fundamental Slides
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Identifiers, Locations, and Variables.. cont.
Examples of valid identifiers:
area , length, X , Y1, abc, d3, st_number
{ these all begin with a letter }
Examples of invalid identifiers:
2Y
{ begins with a digit }
Ali’s
{ contains the symbol ‘ }
st-age { the symbol - is not underscore }
while { it is a keyword }
ab cd { it has a space }
Programming Fundamental Slides
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Identifiers, Location, and Variables.. cont.
Variables:
-The name of the location is the variable name.
-The location content is the value of the variable
- You can change the content of the variable at any
time in the statements of the algorithm.
e.g.
Name of the location
Inside Memory location
employee_name
“Ali Ahmed”
age
35
hourly_rate
3.25
Programming Fundamental Slides
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Identifiers, Location, and Variables.. cont.
Constants:
- You can use a constant identifier in your
algorithm to indicate a constant data.
- You CANNOT change the content of the constant
identifier.
- Use the keyword CONST to indicate a constant
identifier.
e.g.
CONST pi = 3.14
Here, pi is a constant identifier that cannot be changed
Programming Fundamental Slides
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Declaring Identifiers
In
the algorithmic language, we will use
identifiers without declaring them
In C++, you should define any identifier used in
in the program before using it in any statement of
the program.
Ex: int y;
Programming Fundamental Slides
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Expressions
Arithmetic Expression:
- It is composed of operands and arithmetic
operations ( + , - , *, /, MOD).
- Its result is a numeric value
(e.g. 3 + 4 gives 7)
- Operands may be numbers and/or identifiers that
have numeric values
e.g.
x–y
gives 4, if x is 6 and y is 2
x/2
gives 6, if x 12
T MOD 2 gives 0 if T is any even number, and
1 if T is any odd number
Programming Fundamental Slides
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Expressions .. cont.
Logical Expression:
- It is called also Boolean expression.
- It is composed from operands and operators.
- Operands are identifiers that have logical values
- Its result is a logical value (true or false) (see
later).
- Operators are logical: AND , OR, NOT
e.g.
X AND Y
a AND b OR c
where X, Y, a, b, c are defined logical
Programming Fundamental Slides
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Expressions .. cont.
Relational Expression:
- It is composed from operands and operators.
- Operands may be numbers and/or identifiers
that have numeric values
- Its result is a logical value (true or false).
- Operators are relational operators:
<, >, =, ≠, ≤, ≥
e.g.
(a < b) gives true, if value of a is less than value of b
false, if value of a is not less than value of b
(x ≠ y) also gives true or false according to the values of x
and y
Programming Fundamental Slides
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Expressions .. cont.
NOTES
A relational expression may contain arithmetic
sub-expressions,
e.g. ( 3 + 7 ) < (12 * 4 )
2) A logical expression may contain relational and
arithmetic sub-expressions,
e.g.
1x AND y AND ( a > b )
2(2 + t ) < (6 * w ) AND ( p = q )
1)
Programming Fundamental Slides
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Operator Precedence
Expressions are evaluated according to the
precedence rule.
Precedence Rule:
- Each operator has its own precedence that
indicates the order of evaluation.
- If the expression has operators of the same
precedence, then the evaluation starts from
left of expression to the right.
Programming Fundamental Slides
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Operator Precedence .. cont.
Operator
(
++, - – ,
NOT
*, /, MOD
+, <, <=, >, >=
= , !=
AND
OR
Description
parentheses
unary plus, unary minus,
Not
Precedence
Higher
Binary plus, binary minus
Equal, not equal
Assignment
Programming Fundamental Slides
Lower
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Examples
Find the value of the following expression:
(1)
5 + 8 * 2 / 4
16
4
9
(This is the final result)
Programming Fundamental Slides
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Examples .. cont.
(2)
(9 + 3) - 6 / 2
+
5
12
3
9
14
(this is the final result)
Programming Fundamental Slides
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Evaluating Logical Expressions
(1)
The truth table
AND table
AND
True
False
True
True
False
False
False
False
Programming Fundamental Slides
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Evaluating Logical Expressions.. cont.
(2) OR table
OR
True
False
True
True
True
False
True
False
(3) NOT table
NOT
True
False
False
True
Programming Fundamental Slides
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Examples on Logical Expressions
(1)
If x = True, y = False, z = False, find the
value of the expression x AND y OR z
x AND y OR z
False
False
(the final result)
Programming Fundamental Slides
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Examples on Logical Expressions .. cont.
(2) If a = 3, b = 5, x = true, y = false, find the value
of the expression: ( a < b ) AND y OR x
( a < b ) AND y OR x
True
False
True
(the final result)
Programming Fundamental Slides
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