Problem Solving and Computer Programming Introduction CMSC 104 Spring 1999 Problem Solving and Computer Programming The critical words on this slide are "Problem Solving." As you start off in computer science, there are two things you ought to know right away: it isn't about computers and it isn't a science. The discipline we call "computer science" is really the study of algorithms --- of how to do things. An algorithm is a procedure to perform a specific task. In computer science, we're interested in discovering how algorithms work, how they can be measured, which ones are better than others, and how to build and use the best algorithms for any task. This isn't a "science" because it's "active," we aren't just observing things, but trying to make them better. It isn't really about computers because we are most interested in the algorithms themselves. Computers are just one means of actually executing them.

What is Computer Science? Computer science is the study of algorithms --- specific recipes to accomplish a specific task. Not “science” because because goal is to develop algorithms “Computers” are just one means of executing the steps.

Am I in the right class? CMSC 104 CMSC 201 Assumes NO programming experience Does NOT count towards your CS major Prepares you for CMSC 201 CMSC 201 Assumes some programming experience First CMSC course for CS majors More challenging If you can write a program in C, compile it on a Unix system, run it, and debug it if it doesn't work, then you don't belong in this class.

Why Study Computer Science? The purpose of computing is insight, not numbers. R.W. Hamming When you can measure what you are speaking about and express it in numbers, you know something about it, and when you cannot measure it in numbers, your knowledge is of a meager and unsatisfactory kind. -- Kelvin

Getting a “GL” account at UMBC You MUST have a GL account Go to room ECS 005 (in the basement) Sign-on to one of the PCs there Login ID = register No Password Follow the instructions Primary account for homework and projects. You can log in from labs on Campus or from home over the internet or a telephone line.

Changing your Unix password Login by entering your id and password given on the sheet At the Unix prompt type: passwd <Return> You will be prompted for your new password; type it in and press <Return> You will be asked to type the new password again

Changing your Unix password (cont’d) You will be given a message that the password has been changed OR you will be given a message that rejects your new password Passwords should be at least 5 characters long, should be something you will remember. Your password will be rejected if it is a commonly used word or name You must change your password. This should be a simple task, but it can be maddening. The purpose of a password is to keep other people from using the computer while masquerading as you. The operating system assumes that anyone who is entitled to use your account will know your password and that anyone who knows your password is entitled to use your account. Now, since computers first had users, it has been a constant game for some users to masquerade as others. Some people do it purely for the thrill of pulling it off. Some people do it so they can use someone else's time or disk space. And some people do it so that they can raise havoc while someone else gets the blame. In any case, you'll be much better off of no one has your password except you. The secret is to have a password that's too hard to guess, but so easy for you to remember that you don't have to write it down (because someday you'll lose the paper and someone else will find it). This isn't as easy as it looks. Crackers don't sit around and guess passwords themselves, they write programs that try every word --- and pair or triple of words --- in the dictionary. So "habadashery banana" isn't good enough. The trick is to blend in some numbers or punctuation in a way that you'll remember but won't be easy to figure out. So we get "haba-ery b&&a" or "^field&mccoy". One more thing: it took me a frustrating half hour before I realized that the password must be at least 7 characters long.

Computer Science at UMBC CSEE Administrative Offices ECS 210 CSEE Student Services Office ECS 201 CSCM (Sea Scum) Computer Science Council of Majors CSHC (Computer Science Help Center) ECS 332 In the Mechanical Engr Dept.

Some Example Passwords Possible Candidates (but find your own) t0mc@ tomcat g0lf3r golfer $aL3b0@ saleboat (sailboat) Known Loser Str@4d Stratford (too short?) “Second” passwords seem to be easier.

UCS Labs University Computing Services are responsible or all the computers 24 hour labs ECS 021 -- IBMs, MACs Open Labs ECS 005 -- SGI Workstations ECS 104 -- IBMs (but not 104A) ECS 122A -- IBMs Print Dispatch -- ECS 019 ($$)

UCS Labs (Cont'd) Open, but sometimes reserved Hours of Operations ECS 333 -- IBMs ECS 336 - MACs Hours of Operations Monday - Thursday 7 AM - 3 AM Friday 7 AM - Midnight Saturday 8 AM - Midnight Sunday Noon - 3 AM

Consultants vs Tutors UCS Labs are staffed by consultants using software (pine, xrn, netscape, etc.) some text editors (emacs, pico) operating system commands (Unix) cleaning floppy disks communicating with UMBC computers CSHC is staffed by tutors Help with homework and projects emacs and Unix questions ECS 332 -- Hours to be announced

Logging on from Home 2400 baud lines 744 - 8000 high speed lines 744 - 8622 14.4 or 28.8 Settings for both lines No parity, 8 data bits, 1 stop bit On your computer, you must have Communications software (e.g.. Procomm Plus) A modem

telnet Connect to your Internet Service Provider (ISP) Windows 95/NT/98 Start Run telnet gl.umbc.edu

Hardware & Software Needs Do I need my own computer? No, but it is more convenient for you If I have my own computer, can I use it? Sure, but you will using it mostly to login to your GL account or for word processing Do I need a C Compiler? No, and if you buy one, you’ll be wasting your $$$. All programming should be done in your GL account.

Course Overview Introduction to Computer Organization and Architecture Data Representation and Memory Usage Introduction to Operating Systems Problem Solving and Algorithm Development Introduction to Software Engineering Using Top-Down Design Compiling, Linking and Execution C Programming Reuse Based on Algorithm Selection and Design Techniques