1. Data Types, Identifiers, and Expressions
Topics to cover here:
Data types
Variables and Identifiers
Arithmetic and Logical Expressions
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2. Programming Fundamental Slides
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.
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3. Data Types in The Algorithmic Language
Predefined Data Types:
INT : values (e.g , , 12)
operations (e.g. +, -, *, /, , MOD, <, >, =, ≠, ≤, ≥ )
FLOAT : values (e.g , 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.
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4. 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.
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5. 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.
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6. 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.
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7. 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 }
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8. Identifiers, Location, and Variables.. cont.
-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
hourly_rate
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9. 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
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10. 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;
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11. Programming Fundamental Slides
Expressions
Arithmetic Expression:
- It is composed of operands and arithmetic
operations ( + , - , *, /, MOD).
- Its result is a numeric value
(e.g 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 / gives 6, if x 12
T MOD 2 gives 0 if T is any even number, and
1 if T is any odd number
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12. Programming Fundamental Slides
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
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13. Programming Fundamental Slides
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
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14. Programming Fundamental Slides
Expressions .. cont.
NOTES
A relational expression may contain arithmetic sub-expressions,
e.g. ( ) < (12 * 4 )
2) A logical expression may contain relational and arithmetic sub-expressions,
e.g.
x AND y AND ( a > b )
(2 + t ) < (6 * w ) AND ( p = q )
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15. Programming Fundamental Slides
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.
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16. Operator Precedence .. cont.
Description
Operator
Higher
parentheses (
unary plus, unary minus, Not
++, - – , NOT
*, /, MOD
Binary plus, binary minus
+ , -
<, <=, >, >=
Equal, not equal
= , !=
AND OR
Lower
Assignment 
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17. Programming Fundamental Slides
Examples
Find the value of the following expression:
(1) * / 4 16 4
(This is the final result)
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18. Programming Fundamental Slides
Examples .. cont.
( ) / 12 3 9
(this is the final result)
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19. Evaluating Logical Expressions
The truth table
AND table
AND True False
True True False
False False False
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20. Evaluating Logical Expressions.. cont.
(2) OR table
OR True False
True True True
False True False
(3) NOT table
NOT True False
False True
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21. Examples on Logical Expressions
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)
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22. 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)
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