1. 1 Administrivia Lecture hours –Monday, Wednesday, Thursday: 11-11:55am, in L7 –Come to the class in time Labs –2pm-5pm, –Monday: A5-A6, Tuesday: A7-A8, Wednesday: A9- A10, Thursday: A1-A2, Friday: A3-A4 –The lab starts on Tuesday Jan 2, 2007. Since Jan 1 is a holiday, the Monday lab shall be held on Saturday (Jan 6) during 2-5pm. –The lab schedule is given on the course web-page (www.iitk.ac.in/esc101 Tutorial –Tuesday 11-11:55am, Tutorial Block 101-110 –First tutorial on Tuesday Jan 2, 2007.

2. 2 Administrivia Grading: –Exam: 15+15+30 –Two compulsory lab tests: 10+15 (Note: Performance in Lab tests will be taken into consideration while deciding about borderline cases) –Weekly lab sessions: 10 –Tutorials: 5 –Quizzes: 10 (extra credit)

3. 3 Administrivia The course web page will have all relevant info about the course. You should keep checking the web-page for all updates: www.iitk.ac.in/esc101 Text book –Nothing specific: your choice –Suggestion: “Java Elements: Principles of Programming in Java” by Bailey and Bailey –More references are on the webpage You may also visit past course sites through www.iitk.ac.in/esc101

4. 4 What this course is not about This is not a course on programming –You will learn how to solve problems with computers: especially the ones that you cannot solve with paper and pencil quickly –The greater part of the lectures will be devoted to the concepts involved in developing a computer algorithm Sequence of steps that solve a problem –Java will be used as a vehicle to demonstrate the concepts Do not expect to become an expert in Java after taking this course

5. 5 Algorithm The way out is to give a recipe that describes how to obtain the right output from any given input. We use the term algorithm to denote such recipes. Examples: algorithm to multiply two arbitrary integers, algorithm to find the gcd of two integers, etc. For every possible input, an algorithm specifies a sequence of steps which when carried out will give us the output that corresponds to the input. –Although on an input instance an algorithm may specify an arbitrary number of steps to be carried out, the algorithm itself must be finite. – Another property an algorithm must have is that each step it specifies must be effective, that is, it should be possible for the computing agent to carry out the step.

6. 6 Algorithm Consider the problem of computing the product of two numbers by repeated addition. Suppose n1 and n2 are the two numbers, n2 non-negative, then we can find the product by adding n1 n2 times. We will assume for this problem that our computing agent can add two numbers, but arbitrary number of numbers, at any step. With this constraint, an algorithm is: Step 1. Read in the values of n1 and n2. Step 2. Initialize result to 0. Step 3. While n2 is greater than 0, do Steps 4 and 5 Step 4. Obtain the new value of result as (old value of result + n1) Step 5. Obtain the new value of n2 as (old value of n2 -1) Step 6. Print result. (At this point, result = n1*n2).

7. 7 Flowchart

8. 8 Programs Algorithms are informal objects, these are written using natural languages. Although, an algorithm is precise enough for a human being to follow, electronic computers cannot understand these, hence it cannot follow an algorithm to compute an output corresponding to a given input. It needs the algorithm translated in terms of the instructions it is capable to carry out. An algorithm, when translated in terms of what a computer can comprehend, what we have is a program.

9. 9 Anatomy of a computer What you see –A monitor, a keyboard, a mouse, a printer … –Input/Output devices –Through these you ask the computer to do something and the computer tells you the results Need a way to convey your commands to the computer (it is really a stupid device which cannot do anything on its own) –Internally A central processing unit and a scratchpad (often called main memory) accomplish the job

10. 10 Anatomy of a computer Central processing unit does not understand English, not even Java –It only understands two symbols: 0 and 1 –These are called bits (short for binary digits) –You encode your algorithm into a high-level language called Java This is called a program This is harder to understand than English, but easier to understand than a 0-1 encoding How do I encode a program in 0-1? This is used only for storing the program in main memory

11. 11 Anatomy of a computer A friend of yours called compiler translates the program into a binary encoding called an object program –This is almost understandable to the central processing unit (often called a microprocessor) Another friend of yours called a linker adds something more to an object program to convert it to an executable –This is understandable to the CPU –But somehow it needs to get started executing

12. 12 Anatomy of a computer A big boss called operating system loads the executable in main memory and hands over the control to the CPU –Now the CPU starts executing your program (essentially the binary executable) –Once in a while it prints something on the monitor and you appreciate that Notice that it is not doing anything on its own, only doing whatever you have asked it to do –At some point the CPU completes the execution and you have all the results

13. 13 A simple program Let’s write a program in English (almost) –Want to add five numbers a, b, c, d, e and print the result on monitor print (monitor, a+b+c+d+e) –print is used as a function which takes two arguments: where to print and what to print –A binary translation of this could convert each character i.e. p, r, i, n, t, (, m, … into a binary string e.g., p is the 16 th alphabet, so represent it as 16 zeros; put a 1 to mark the end of a character –Now I can design a CPU which can understand this translation and execute my program (caution: this is just an example)

14. 14 Printing on monitor /* Example of multiline comment; This is our first Program */ class printcoursename{ public static void main(String arg[]){ // This prints name of the course (single line comment) System.out.println("This course is ESc101N"); }

15. 15 Printing on monitor /* Example of multiline comment; This is our second Program. Will print the same thing in a different way. */ class printcoursename{ public static void main(String arg[]){ // This prints name of the course (single line comment) System.out.println("This ” + “course ” + “is ” + “ESc101N”); }

16. 16 Printing numbers class printnumber { public static void main (String args[]){ // Notice that I can use args also // because it is a variable name and can be // anything. int var1; // Declaration var1 = 124; // Operator and expression System.out.println("Value of var1 is: "+var1); }

17. 17 Lab #1 Learn to use the UNIX environment –How to create a file (this where you store your programs) –How to create and navigate through directory (this where you store your files) –How to copy files from one directory to another –And more: www.iitk.ac.in/esc101/linux.pdf –Lab is upstairs in CC: Your tutor will be there in the lab.