Summary Programming Logic and Design Ch 2

Chapter 2

Declaring and using variables and constants
 Data type- a classification that describes the following:
 What values can be held by the item
 How item is stored in computer memory
 What operations can be performed on the item
 Numeric- data that consists of numbers/decimals, arithmetic operations performed
 Integer values- whole numbers / Floating point values (real numbers) -
decimal numbers
 String- data items that are non-numeric, cannot be used in arithmetic operations
 Numeric constant -Contains numbers that does not change
 String constant (Alphanumeric values) - Enclosed in quotation marks, contains characters
and numbers
 Variable -named memory locations, content can vary
 Numeric variable- holds digits, performs mathematical operations
 String variable- holds text, letter, special characters
 Declaration is a statement that provides a variable's:
 Data type
 Identifier (variable’s name)
 Optionally, an initial value
 Type-safety -Prevents assigning values of an incorrect data type
 Identifier- variable name
 Choose reasonable and descriptive name for variables
 Most languages allow letters and digits
 Some languages allow hyphens
 Reserved keywords are not allowed (num/string)
 Variable names- case sensitive
 Must be one word
 Must start with a letter
 Should have appropriate meaning
Variable Naming
Camel casing (lower) hourlyWage Snake casing hourly_wage
Pascal casing (upper) HourlyWage Underscore casing Hourly_Wage
Hungarian notation numHourlyWage Kebob casing hourly-wage


 Assignment statement- first calculates myNumber * 2, then stores computed value in
myAnswer
 set myAnswer = myNumber * 2
 Assignment operator
 Binary operator- requires two operands - one on each side

,  Operates from right to left, right-associativity or right-to-left associativity
 The result to the left of an assignment operator is called a Lvalue
 Initializing the variable - declare a starting value, variables must be declared before used in
program
 num yourSalary = 14.55 / num yourSalary
 string yourName = “Janita” / string yourName
 Garbage – a variable’s unknown value, till it is given a value (input yourSalary)
 Named constant- Uppercase with underscores
 Can be assigned a value only once
 Assign a useful name to a value that will never be changed during a program’s execution,
or change once to change all instances
 Magic number
 Unnamed constant
 Use taxAmount = price * SALES_TAX_AMOUNT instead of taxAmount = price * .06 (magic
number)


Performing arithmetic operations
 Standard arithmetic operators:
+ (plus sign)- addition * (asterisk)- multiplication = (equal)- assignment
− (minus sign)- / (slash)- division
subtraction


 Rules of precedence (Order of operations)
Parenthesis
 Dictate the order in which operations in the same statement are Multiplication and
carried out Division
Addition and
 All the arithmetic operators have left-to-right associativity
subtraction
 Dividing an integer by another integer is a special case
 Dividing two integers results in an integer, and any fractional part of the result is lost
 The decimal portion of the result is cut off, or truncated
 A remainder operator (modulo operator/ modulus operator) contains remainder of a
division operation
 24 Mod 10 is 4, Because when 24 is divided by 10, 4 is the remainder


The advantages of modularization
 Modules -Subunit of programming problem (subroutines, procedures, functions, or methods)
 Call a module is to use its name to invoke the module, causing it to execute
 Modularization -Breaking down a large program into modules (functional
decomposition)
 Abstraction
 Paying attention to important properties while ignoring nonessential details
 One broad statement corresponds to dozens of machine instructions
 Multiple programmers can work on one problem