Introduction to Algorithmic Processes CMPSC 201C Fall 2000

Software Design Process  Requirements specification – What should this application do?  Analysis – What is needed to perform this task?  Design – How will you accomplish this task (algorithm)?  Implementation – Translate algorithm into a computer language (code).  Reuse review – Are you reusing the objects correctly?  Maintenance and upgrades – How should program be changed with use and time?

Requirement Specification  Ask questions!  What should this program do?  Who will be using it?  What is the program’s expected lifetime?  Etc.  Rewrite problem in your own words.  Document.  Do not skip this step!

Analysis  Determine objects, variables, constants, etc. that you need to complete task.  What properties do these need?

Design  Develop the logic.  Explore different approaches.  Develop the algorithm.  Diagram logic flow and interaction between different parts.  Develop a set of test data.  Documentation.

Implementation  Translate algorithm to computer language.  Compile (checks for syntax errors) and link (combines your code with library programs or other modules).  Document code.  Test.  Modify code as needed to correct errors.

Reuse review  Are items (objects, sections of code etc.) that you may want to reuse organized together and identified?

Upgrade and Maintenance  Modify to meet changing needs.  Modify to run smoother.  Fix errors (“bugs”).  Document.

Syntax  Grammar rules  Punctuation  Semicolons (;)  Braces ({)  Slashes (/)  Etc.

Style Rules  Use meaningful, descriptive names.  Capitalize in a consistent manner.  Document.  At beginning to define problem, variables, constants etc.  Throughout code to explain specific sections.  Use spacing and indentation to help delineate sections of code and logic flow.  See figure 1.10

Questions  ????

Memory

Operating system Your Program data

Variables and Constants  Names for memory locations so the programmer does not have to use cell address!  Variable - data stored in that memory location will change throughout execution of the program.  Constant - data is set at compile time and cannot be changed without recompiling the program.

What is an Identifier?  An identifier is the name used for a data object (a variable or a constant), or for a function, or for a data type, within a C++ source program.  Names (identifiers) in C++ are dependent on case, e.g. someVariable is not the same as SomeVariable.  A keyword (see appendix E) may not be used as an identifier.

Identifiers (Names)  An identifier must start with a letter or underscore,  and be followed by zero or more letters  (A-Z, a-z), digits (0-9), or underscores.  VALID  age_of_dogTaxRate98  PrintHeading AgeOfHorse  NOT VALID (Why?)  age#98TaxRateAge-Of-Cat

More about Identifiers (Names)  Some C++ compilers recognize only the first 32 characters of an identifier as significant.  Then these identifiers are considered the same:  Age_Of_This_Old_Rhinoceros_At_My_Zoo  Age_Of_This_Old_Rhinoceros_At_My_Safari  What about these?  Age_Of_This_Old_Rhinoceros_At_My_Zoo  AgE_Of_This_Old_Rhinoceros_At_My_Zoo

Variables  Need variables for data that is input  Need variables for data that is output  Variable names should be descriptive and easily remembered.  Variables need to be declared before they can be used in a program.

Variable Declaration & Assignment  Variable declaration consists of the data type of the variable and the variable name.  int sampleID  double sulfurContent  Variable assignment stores the result of an expression into the variable.  variablename = expression  The declaration may in some cases be combined with the assignment.  double poundsDioxide = sulfurContent/100

Data Types  Numbers  Integers - whole numbers  Floating Point - contain fractional parts  Characters

Integers  short to  unsigned short0 to  int to  unsigned int0 to  long to  unsigned long0 to

Integers  Long integers require more memory space than int or short.  However, errors may occur if int value is larger than 32767, e.g may be represented as 1 or -1 depending on the compiler.

Floating Point  Float  to  with 6 significant digits  double  to  with 15 significant digits  long double  to  with 19 significant digits

Floating Point  Required memory increases with increased range and significant digits.  Required time for calculations increase with significant digits.

Character  Used to represent characters - letters, spaces, numbers not used for arithmetic operations  char variable can store a single character or an escape sequence.  ‘A’, ‘b’, ‘ ‘,  ‘\n’new line  ‘\t’tab  ‘\f’form feed (new page)

Arithmetic Operations  Unary - one operand  positive and negative  +a or -zebra  Binary - two operands  addition+var1 + var2  subtraction-var1 - var2  multiplication*var1 * var2  division/var1 / var2  remainder (modulus)%var1 % var2

Precedence  Parenthesis  Unary operations  Multiplication, Division, Remainder  Addition, Subtraction

Questions?

Arithmetic Operations  In general expression involving only integers will result in an integer and expressions involving only floating point numbers will result in a floating point number.  Mixed expressions involving both floating point and integer numbers will result in a floating point number. However this result may be unexpected.

Integer Division  Remember that integers are whole numbers.  Integer division may have unintended results depending on the data type of the variables involved.  int var1 = 10  int var2 = var1 / 8(1)  float var3 = var1 / 8(1.0)  float var4 = var1 / 8.0(1.25)

Integer Division (Cont.)  The expression  5.5 * 7 /2  is not the same as the expression  7 / 2 *5.5

Data Type Casting  Casting is the explicit conversion of data type within an expression.  Suppose you have declared two int variables distance and time and the float variable speed. The expression speed = distance/time would lose the fractional component of speed. To avoid this loss you could do one the following.  speed = float(distance) / time  speed = distance / float (time)  speed = float (distance) / float (time)

Data Type Casting (Cont.)  Note that the expression  speed = float (distance / time)  would still lose the fractional part of speed.

Data Type Casting (Cont.)  When a float variable is casted (converted) to an integer value, value is truncated not rounded.  int (12.6) is 12 not 13  To round add 0.5 before converting.  int ( ) is 13 while  int ( ) is 12

Questions?

General Syntax Rules  Statements that should be executed should end in a semicolon (;)  Comments are designated with // or /* & */  Library header files require a line similar to #include

Input/Output  cin >> variable name;  cout<< “text”, variables, expressions;  require the library header file iostream.h (the line #include must be included in your source code.)

Questions ????