Department of Computer and Information Science, School of Science, IUPUI

1. Department of Computer and Information Science,School of Science, IUPUI CSCI N305 Introduction to Computers - Languages

2. CPU Control Circuit (ex: PC: Program Counter) Memory I/O ALU Computer Organization A Typical Von-Neumann Architecture Example: • Input unit • Output unit • Memory unit • Arithmetic and logic unit (ALU) • Central processing unit (CPU) • Secondary storage unit

3. Programming Languages • Machine languages (machine dependent) • Native tongue of a particular kind of computer. Each instruction is a binary string. The code is used to indicate the operations to be performed and the memory cells to be addressed. This form is easiest form of computers to understand, but is most difficult for a person to understand. • Strings of numbers giving machine specific instructions • Example: +1300042774 • +1400593419 • +1200274027

4. Programming Languages (cont.) • Assembly languages (machine dependent) • English-like abbreviations representing elementary computer operations (translated via assemblers) • Again specific to only one type of computer. Uses descriptive names for operations and data, e.g. , “LOAD value”, “ADD delta”, “STORE value”. Assemblers will translate these to machine languages. Intermediate level. Somewhat descriptive, but basically following the machine instructions. • Example: LOAD BASEPAY ADD OVERPAY STORE GROSSPAY

5. a 10 Before b 7 a 17 After b 7 Programming Languages (cont.) • High-level languages (machine independent) • Codes similar to everyday English • High-level languages: Write program instructions called statement that resemble a limited version of English. e.g., the statement “value = value + delta”. Portable, meaning it can be used on different types of computers without modifications. Compilers translate them to machine languages. Examples are FORTRAN, PASCAL, COBOL, C, C++, BASIC etc. • Use mathematical notations (translated via compilers) Example: grossPay = basePay + overTimePay Example: Statement: a= a + b

6. Application Area Origin of Name Language FORTRAN Scientific programming Formula Translation COBOL Business data Processing Common Business-Oriented Language Lisp Artificial Intelligence (AI) List Processing C System Programming Predecessor B Prolog AI Logic Programming Ada Real-time distributed systems Ada Augusta Byron & Charles Babbage Smalltalk GUI, OOP Objects “talk” via message C++ Supports object & OOP C (++ is the increment operator) JAVA SupportsWeb programming Originally named “Oak” Programming Languages (cont.) • Structured programming • Disciplined approach to writing programs • Clear, easy to test and debug and easy to modify • Multitasking • Specifying that many activities run in parallel (still timesliced)

7. Semantic Gap • A “semantic gap” exists between the amount of information conveyed in assembly language v high level languages. Consider the following C single statement: x = x + 3; • This single statement may require many assembly language statements (operations): Load memory location 24 into accumulator Add a constant 3 to the accumulator Store accumulator in memory location 24 • The number of executable statement expands greatly during the translation process from a high level language into assembly language.

8. C Programming Language • C • High-level general-purpose language developed in 1972 at AT&T Bell Lab. By Dennis Ritchie from two previous programming BCPL and B • Originally developed to write the UNIX operating system • Hardware independent (portable) • By late 1970's C had evolved to "Traditional C" • Today, virtually all new operating systems are written in C or C++. • The current standard in C is ANSI C. • C++ is a more advanced version of C, incorporating among other things, the object-oriented constructs • Standardization • Many slight variations of C existed, and were incompatible • Committee formed to create a "unambiguous, machine-independent" definition • Standard created in 1989, updated in 1999 • C has become a popular language industry due its power and flexibility

9. The C Standard Library • C programs consist of pieces/modules called functions • A programmer can create his own functions • Advantage: the programmer knows exactly how it works • Disadvantage: time consuming • Programmers will often use the C library functions • Use these as building blocks • Avoid re-inventing the wheel • If a pre-made function exists, generally best to use it rather than write your own • Library functions carefully written, efficient, and portable

10. The C Standard Library (cont.) • The Key Software Trend: Objects in C++ and JAVA • Reusable software components that model items in the real world • Meaningful software units: ex: Date objects, time objects, audio objects, video objects, file objects, record objects…any noun can be represented as an object • More understandable, better organized, and easier to maintain than procedural programming • Favor modularity

11. The C Standard Library #include <stdio.h> main() { int i; for (i = 0; i ++; i < 10) { printf ("Hello World!\n"); } }

12. Phases of C Programs: 1. Program is created in the editor and stored on disk Editor Disk 2. Preprocessor program processes the code Preprocessor Disk 3. Compiler creates object code and stores it on disk. Compiler Disk Linker Disk 4. Linker links the object code with the libraries Primary Memory Loader 5. Loader puts program in memory. Disk Primary Memory CPU 6. CPU takes each instruction and executes it, possibly storing new data values as the program executes A Typical C Program Development Environment 1. Edit 2. Preprocess 3. Compile 4. Link 5. Load 6. Execute

13. A Typical C Program Development Environment (cont.) Enter the program code and save as a source (*.c) file using Word Processor (editor) Revised source file Source (.c) file on disk (Format: text) Correct syntax errors Compiler attempts to translate the program into machine code Failure List of errors Success New object (*.obj) files (Format: binary) The linker links the new object file with other object files Other object (*.obj) files Input data Executable (*.exe, *.out) file (Format: binary) Welcome to CSCI230 The loader places the executable file into memory Executable program in memory Results • Procedure to Prepare a C Program for Execution

14. Constructs in C Language • Type Declarations: ex: int, float,… • I/O: ex: printf(), scanf() • Arithmetic and LogicalOperations: ex: +,-,*,/,%,>,<,==,… • Arrays, Pointers, Structures, Unions, … • Functions • Arguments & return values • Recursion • Control Mechanisms: ex: if, else, while, for,… • Characters & Strings: ex: strcat(), strcpy(), … • File Processing: ex:fopen(), fclose(), … • Pre-processor: ex: #define … • Misc. • bit operations, ...

15. Command-line Interface Graphical User Interface (GUI) UNIX MacOS MS_DOS Windows VMS X Windows (linux and solaris) Operation System (OS) • Responsibilities: • Communicating with the computer user • Managing allocation of memory, of processor time, and of other resources for various tasks • I/O handling: BIOS vs DOS services (Interrupts) • Read/Write data from secondary storage • Evolution of Operating Systems • Batch processing: do only one job or task at a time • Operating systems: manage transitions between jobs and Increase throughput (amount of work computers process) • Multiprogramming: Computer resources are shared by many jobs or tasks • Timesharing: Technique used to implement multiprogramming where the computer runs a small portion of one user’s job then moves on to service the next user

16. Application Software • Developed to assist a computer user in accomplishing special tasks • ex: word processing applications: MS-word or Word-perfect • ex: Spreadsheet applications: Lotus1-2-3, Excel • ex: Database: Oracle, MS-Access • Software Development Life Cycle (SDLC) • Problem: specify the problem requirements • Analysis: analyze the problem • Design: design the algorithm to solve the problem • Implementation: Implement the algorithm • Testing: test and verify the completed program • Maintenance: maintain and update the program