Programming Fundamental Slides1 Data Types, Identifiers, and Expressions Topics to cover here: Data types Variables and Identifiers Arithmetic and Logical Expressions

Programming Fundamental Slides2 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 Slides3 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 Slides4 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 Slides5 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 Slides6 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 Slides7 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 Slides8 Identifiers, Location, and Variables.. c ont. 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 Slides9 Identifiers, Location, and Variables.. c ont. 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 Slides10 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 Slides11 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 / 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 Slides12 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 Slides13 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 Slides14 Expressions.. cont. NOTES 1) 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. 1- x AND y AND ( a > b ) 2- (2 + t ) < (6 * w ) AND ( p = q )

Programming Fundamental Slides15 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 Slides16 Operator Precedence.. cont. PrecedenceDescriptionOperator Higherparentheses ( unary plus, unary minus, Not ++, - –, NOT *, /, MOD Binary plus, binary minus +, -, >= Equal, not equal =, != AND OR LowerAssignment 

Programming Fundamental Slides17 Examples Find the value of the following expression: (1) * 2 / (This is the final result)

Programming Fundamental Slides18 Examples.. cont. (2) ( ) - 6 / (this is the final result)

Programming Fundamental Slides19 Evaluating Logical Expressions The truth table (1) AND table AND True False True True False False False False

Programming Fundamental Slides20 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 Slides21 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 Slides22 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)