Programming and Languages Dept. of Computer and Information Science IUPUI

Programming as Problem Solving Problem solving principles: 1. Completely understand the problem 2. Devise a plan to solve it 3. Carry out the plan 4. Review the results Developing a Program: 1. Analyze the problem 2. Design the program 3. Code the program 4. Test the program

 Hardware  Machine code  Assemblers  Compilers  Interpreters Progression

Hardware encoding  Change physical structure of machine  Extremely tedious  Very difficult  Prone to error

Programming Languages  Programming languages allow programmers to code software.  The three major families of languages are:  Machine languages  Assembly languages  High-Level languages

Machine Language  Stored Language Concept  Von Neumann  Treat Instructions as data  Comprised of 1s and 0s  The “native” language of a computer  Difficult to program – one misplaced 1 or 0 will cause the program to fail.  Example of code:

Assembly Languages  Mnemonics  Labeled cells  somewhat easier on programmers  Assembly languages are a step towards easier programming.  Assembly languages are comprised of a set of elemental commands which are tied to a specific processor.  Assembly language code needs to be translated to machine language before the computer processes it.  Example: ADD ,

High-level Language  Typed in near-human language  Converted to assembler  Much easier on programmers  Can be assembled or compiled  Language is still very precise, but more nearly readable  High-level languages represent a giant leap towards easier programming.  The syntax of HL languages is similar to English.  Historically, we divide HL languages into two groups:  Procedural languages  Object-Oriented languages (OOP)

Procedural Languages  Early high-level languages are typically called procedural languages.  Procedural languages are characterized by sequential sets of linear commands. The focus of such languages is on structure.  Examples include C, COBOL, Fortran, LISP, Perl, HTML, VBScript

 Most object-oriented languages are high-level languages.  The focus of OOP languages is not on structure, but on modeling data.  Programmers code using “blueprints” of data models called classes.  Examples of OOP languages include C++, Visual Basic.NET and Java. Object-oriented

Interpreting  Some programs are translated using an interpreter. Such programs are translated line-by-line instead of all at once (like compiled programs). Interpreted programs generally translate quicker than compiled programs, but have a slower execution speed.  Interpreter runs in background  Instructions are translated in real time  high-level code is distributed  More flexible  Slower

Compiling  Some programs are translated using a compiler. When programs are compiled, they are translated all at once. Compiled programs typically execute more quickly than interpreted programs, but have a slower translation speed.  Compiler converts entire program into machine language  binary code is distributed  Less flexible  Faster  Regardless of the HL Language, all HL programs need to be translated to machine code so that a computer can process the program.

Structured Programming  A method for designing and coding programs in a systematic, organized manner.  It combines the principles of top-down design, modularity and the use of the three accepted control structures of sequence, repetition and selection.

Control Structures  Sequence –in sequential order.  The simplest of control structures – start at the beginning and continue in sequential order.  Selection – selectively execute statements  Called a branch, it requires a condition to determine when to execute statements.

Control Structures  Repetition – repeat statements more than once  Called a loop, it needs a stop condition, I.e, the program will continue to loop until some condition is met.

Sequence Structure  Start – where the program begins  Input – data to be used for the program  Step One, Step Two, etc. – the sequence of the program until it finishes  No deviation

Selection Structure  Start the program  Input – data to be used  Asking the question; only one question  The answer, YES or NO  Depending on the answer, the action to be taken  The program moves on or ends

Loop Structure  Program starts  The condition is set  Input – ask for password  Answer is evaluated, compared to condition  If no, action of asking for password continues until input of correct password

Event-Driven Programming  In an event-driven program, the flow of control is based on the user’s clicking on menus and buttons, etc. These user actions are called events.  Event-driven programming still uses the basic principles of structured programming – program modules, control structures, good programming style, and program testing.

Types of Errors  Syntax – wrong grammar, i.e., breaking the rules of how to write the language  Forgetting punctuation, misspelling keyword  The program will not run at all with syntax errors  Logic - the program runs, but does not produce the expected results.  Using an incorrect formula, incorrect sequence of statements, etc.

Programming Example  Simple programming problem: Convert a price from British pounds into Dollars.  Pseudocode Input the price of the item, PoundPrice, in pounds Compute the price of the item in dollars: Set DollarPrice = 1.62 * PoundPrice Write DollarPrice

Programming Example  Translating to Basic: INPUT PoundPrice LET DollarPrice = 1.62 * PoundPrice PRINT DollarPrice END

<!– var strUserName = ""; // user's name, this is a STRING var strUserCity = ""; // user's city, this is a STRING var intNumLetters = 0; // number of letters in user's first name, this is an INTEGER var strMessage = "" // output to the user, this is a STRING strUserName = window.prompt("What is your name?"); //this is asking for the user's name strUserCity = window.prompt("Where do you live?"); //this is asking what city does the user live in strMessage = ("Hello, "); strMessage += (strUserName.toUpperCase()); //this puts the user's name into uppercase letters strMessage += (". You live in "); strMessage += (strUserCity.toUpperCase()); //this puts the user's city into uppercase letters window.alert(strMessage); //this is the message given to the user intNumLetters = strUserName.length; // output to the user window.alert("There are " +intNumLetters+" letters in your first name."); //this is a string method, it is counting the number of letters in the user's name //this tells the user how many letters that user has in their name // -->