CSC 200 Spring 2006 Instructor: Matt Kayala

What is a “Computer”? We all use them for all kinds of tasks: –Games –Word Processing Good at repetitive tasks. Tasks not built in need to be programmed.

Program/Programming Computers can perform a small set of instructions –Add, Subtract, Send to Screen Program – Sequence of detailed steps to perform a task. Programming – the act of designing and implementing a program

Von Neumann Architecture Programs and Data stored in memory ALU can do limited number of ops Control Unit “fetches” instructions from memory

Machine Code At Von Neumann (hardware) level, instructions very primitive –(a) Move data stored in mem loc 19D8 to register B. –(b) Subtract 100 from register B. –(c) If result is negative, jump to instruction at mem loc 102C. In fact, all instructions encoded as numbers. Example: Instruction (a) might be encoded as “ D8” Not very readable/user friendly.

Assembly Language To move away from number encodings, people began using mnemonics for instructions Example: Instruction (a) might be written as “mov 19D8”. Mnemonics easily translated to Machine Code. Better, but still not great. –Lots of instructions still, even for simple tasks. –Different hardware (processors) all have different assembly langs.

Higher Level Languages In the 1950’s higher level languages appeared. Example: The whole set of three instructions two slides back might be written (abstractly) –“if (theNum < 100) then…” The key to these langs was the development of “Compilers”, special progs which translate higher langs to machine code. Better, and the best you’re gonna get: –Hardware independent –Many “flavors”

Language Design and Evolution 100’s of different languages Specific vs. General Purpose –Java, C++, Pascal – General –TSQL, Prolog – Specific Grown vs. Planned –C++ - Grown –Pascal - Planned

Simple C++ Program

Notes on Simple Program Case Sensitive –“main” != “Main” Free-form –Whitespace (spaces, tabs, new lines) does not matter –Format chosen for clarity (line spacing, indentation) Also, source code needs to be “compiled”

Compilation Process For semester we will use Dev C++, an IDE. IDE – Integrated Development Environment Does all of the above steps. Also includes a “debugger”.

Errors Two types of errors in programs: –Syntax – keep source from compiling. –Logic – compiles, but errors in logic make program perform not as designed. Errors WILL happen! Program in a manner to minimize. –Structured, modular thought. –Follow the Edit – Compile – Debug – Test Process.

Testing and Debugging Debugger – Special program to track down syntax errors and run program traces. Debugging – the act of fixing these errors. Testing – job of the programmer to test for logic errors. Trace – Stepping through a program one line at a time to discover errors.

Algorithms Programming is really process of designing and implementing algorithms Algorithm – series of steps to complete a specific task where each step is: –Unambiguous –Executable –Terminating Example: Calculate interest accrual over n years. Counterexample: Paint a masterpiece.