Programs

1. Programs • A program is a stored set of instructions that can be interpreted and executed by a computer. This applies to the written program which is just a text document and to the electronic version which is a stream of non-human readable binary digits ( 0 and 1). • Two Categories of Programs: • System • Multitasking/Single Tasking • Multiuser/Single User • Ex. operating system • Applications • Ex. Word Processor

2. Characteristics of a Well Designed and Written Program The program must operate properly Correctness – meets the specifications Integrity – does not create ‘side-effects’ Reliable – does not fail (crash, blue-screen) Usable – easy to learn, screen presentation Efficient – make good use of resources Secure – protection from external threats The program must be able to be maintained & revised Documentation Organization Other desirable characteristics: Expandability, Portability

3. Programming Languages A programming language is a language used to write instructions for acomputer. It lets the programmer express data processing in a symbolic manner without regard to machine-specific details. Low-level language: First level above the binary language (machine language) of the computer and is specific to the computer’s architecture. High-level language: Closer to human language Depending upon the language, all programming languages must be translated by application programs called compilers, assemblers, or interpreters into executable machine language. The C++ programming language uses a compiler.

4. Overview of the Programming Process • Clearly define what the program should do • State in writing what the program is to do • What information does it need? List the inputs and give them names. • How is it going to acquire that information? (keyboard, file, instrument, etc.) • How should the information be processed? • What should be the product(s) (output(s)) of the program? List them and give them names. • How should be outputs be presented? (display on screen, print, create file, etc.) • Create an algorithm (step by step procedure) to solve the problem (many tools are available for this process) • pseudocode – Hybrid of code like and English like statements delineating the steps involved to create a program that meets the problem conditions • flow charts – visual aid to help visualize the solution • UML – Unified Modeling Language • others • Create and test the program • Write the code (text file*) • Save the file • Compile it to create a machine readable form • Run it with one or more sets of test data (Note: Test data should include all possible situations) • Correct errors and go back to the start of this list

5. The Translation Process A human readable document containing instructions written in a high-level language (in our case, C++) is created and passed off to a program called a compiler that can process the C++ statement into something the computer hardware can understand and execute. **** Source code – text document containing the human readable written instructions defining the algorithm (procedure) the computer is to follow to accomplish a task or tasks. Preprocessor – part of the compiler program used to translate the written document into machine language. Some of the instructions in the source code tell the compiler that it needs to modify or amplify the other instructions. The statements in the source code preceded by # are for the preprocessor. Object Code created - Compiler processes the code produced by the preprocessor into ‘almost machine executable code’ called object code that contains the translated program and references to pieces of code provided by the language to perform common tasks. Linking - These references need to be ‘linked’ together to form the final executable code.

6. Algorithm Step by step outline of how to solve a problem. Note: The program is the coded implementation of the algorithm Example: Problem: Given the price of an object on the price tag, determine the sales tax and actual sales price which includes the sales tax. Algorithm (Steps used to solve the problem): Get the amount on the price tag. Compute the sales tax. (Sales tax = Price Tag * Sales) Compute the selling price. (Selling Price = Price Tag + Sales tax) Display the Sales tax and the Selling Price

7. Program Source CodeProvide instructions for the compiler and the computer AND important information for the programmer Source code is just a human readable text file with a file extension indicating the language that the programmer used to write the program. For C++ that file extension is ‘.cpp’. As a beginner your programs will start with three basic sections • header comment • compiler directives • program body

8. Header Comment The header comment appears at the top of the file and contains information for programmers who need to understand the program. Examples of kinds of Information in the header comment • Identification of the programmer and his/her organization • Name/location of source file • Statement of the task(s) the program is to perform • Inputs required and their format • Outputs produced • Error code description • Other information required by the company

9. Compiler Directives Compiler directives are C++ statements that tell the compiler about features of the program that it will need to know about before it starts translating the rest of the program. You will use the following two compiler directives in every program you write for this class. Others will be added as we go along. • #include <iostream> • using namespace std;

10. Program Body The program body is made up of sections of code called functions. EVERY program will have a function called ‘main’ which is always the starting point for code execution. Functions contain the code statements that instruct the computer to carry out the algorithm you want to use to carry out the task(s) the program is to perform. For now, your programs will contain only 1 function, the one that is always required, main.

11. Elements of a C++ Program • Key Words • Reserved – cannot be used in other than in their intended fashion • Lower case – always written in lower case • Operators • Symbols such as +,-,*,=, etc. that require operands and ‘operate’ on the operands • Programmer Defined Symbolic Names • Cannot be the same as Key Words • Case sensitive • Usually follow a style dictated by your employer or instructor • Punctuation • Semicolons, Commas • Comments • /* Used for programmer notes spanning multiple lines. Everything between these two symbols is for human readers of the program text and is ignored by the compiler */ • Preceded by // on each new line they appear (single line comments) • Used to document a program • Grouping Symbols • Used to enclose sections of code or items that belong together • () and {}

12. Example C++ Program (color-coded) /*Given the price tag of a store item, this program displays the sales tax and the final cost with sales tax * included. */ #include <iostream> using namespace std: int main() { doublemarked_price, tax, selling_price; //Get the price on the price tag cout<< “What is the price indicated on the price tag?”; cin>>marked_price; //Calculate the sales tax tax= marked_price* .0825; //Calculate the final selling price selling_price=marked_price+tax; //Display the tax and final selling price cout<< “Sales tax: “ << tax<< endl; cout<< “Final selling price: “ << selling_price<<endl; return 0; } Legend Key Word Operator Programmer defined name Punctuation Comment Grouping symbols Literal

13. Syntax vs. Style Syntax Style Required formatting Statements are terminated with ‘;’ () surround function arguments {} enclose code belonging to a unit ‘main’ function required and is the entry point for your program Key words are all lower case ‘,’ separates members of a list Self or industry (or instructor) imposed formatting Convention for naming variables Named constants (to be discussed later) are ALL CAPS Indentation required for readability Note: C++ doesn’t care about style. Only employers, programmers AND instructors reading the code care about style

14. IDE – Integrated Development EnvironmentEclipse Designed to maximize programmer productivity by providing tightly-knit components with a similar user interface so the programmer has to do less mode switching versus using discrete development programs. Because an IDE is a complicated piece of software by its very nature, higher productivity only occurs after a lengthy learning process. Typically an IDE is dedicated to a specific programming language. However, there are some multiple-language IDEs, such as Eclipse,Oracle JDeveloper, recent versions of NetBeans and Microsoft Visual Studio (many others). We will be using Eclipse C++ IDE.

15. Two Kinds of Errors Syntax errors – failure to follow the rules of statement structure Note: Program will usually fail to compile Ex. missing semi-colons, un-paired grouping symbols, undeclared variables, typos Logic errors – program organization does not lead to the correct result Note: Program does compile but does not ‘work’

16. Operating Systems and Newlines Newline – sequence of one or two non-human readable characters indicating that a new line of text should begin. CR – carriage return LF – line feed CR/LF – used in Windows and DOS operating systems LF – used in Unix and Unix like operating systems including Mac OS X CR – used in Mac operating system prior to Mac OS X Note: Eclipse creates and expects the Unix format. Files created in the Eclipse IDE will have the Unix format.