1. WELCOME To ESC101N: Fundamentals of Computing Instructor: Ajai Jain ajain@cse.iitk.ac.in

2. Lecture hours –Monday, Wednesday, Thursday: 8-9am, L17 –Please come to class in time Labs –2pm-5pm, 11 lab sessions –No lab this week Tutorial –Tuesday 8-9 am, Tutorial Block 101-110 –No tutorial this week

3. Administrivia Grading - Exam: 15+15+30 –Project and/or lab test :20 –Weekly lab sessions: 10 –Two surprise quizzes: 10 Held in tutorial sessions No make up for surprise quizzes (so come to tutorial regularly)

4. There will be a course web page with all info Text book –Nothing specific: your choice –Suggestion: “Java Elements: Principles of Programming in Java” by Bailey and Bailey –More references are on the webpage Visit past course sites: www.iitk.ac.in/esc101

5. What this course is not about This is NOT a course on Java –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

6. 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

7. 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

8. Anatomy of a computer A system software 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 software 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

9. Anatomy of a computer An 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

10. 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 letter of 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)

11. “The Computing Stack” Problem Algorithm Program (HLLs) HLL Compiler/Linker Executable binary Operating System Microarchitecture Circuits Transistors ESC101N HLL=Java Central in CS Hardware/ software interface Hardware

12. Data Representation Recap Talking to the computer –Numbers Data types –Integer and long integer –Floating-point and double –Character and String –Boolean

13. Recap Algorithms Programs Compilers: executables (binary: 0 and 1) Operating systems Central processing unit (CPU) and memory

14. Numbers How does computer understand numbers? –Knows only two symbols –We are mostly familiar with decimal numbers –General number representation in arbitrary base –An algorithm for converting between bases –Special case: base=2 (binary) –Is there a decimal to binary converter inside the computer? Compiler does it –Negative numbers? Two representation conventions: sign-magnitude representation and 2’s complement representation

15. 2’s complement Steps involved in converting decimal to 2’s complement –Decide the number of bits (should be at least 2+integer part of log 2 |N|) –Write the magnitude in binary and append zeros at the front to fill up the remaining bits (this is 2’s complement of the positive number) –Flip all bits (this is 1’s complement of the positive number) –Add 1 to it (this is 2’s complement representation of the negative number)

16. 2’s complement 2’s complement to decimal: –Write down the polynomial expansion in base 2 –Append a negative sign to the leading coefficient Comparison of 2’s complement and sign- magnitude –Range in sign-magnitude with n bits –Range in 2’s complement with n bits –Benefits of 2’s complement in binary arithmetic: makes logic design simpler –All computers and calculators use 2’s complement representation

17. Variables Anything that stores a value –Symbols made up of characters: A-Z, a-z, 0-9, _, $, … –Called identifiers –Must start with a letter or _ or $ –Examples: dayOfTheWeek, day_of_the_week, dayoftheweek, _dayoftheweek, myname, myName, … –Constants are not variables: 7, 100, 2.5, … –Variables are useful for holding non-constant values

18. Data types Integer and Long integer –int and long –Called keywords: will learn more keywords –Keywords cannot be used as identifiers –Example: int x; – x is the variable name which we have declared as an integer – x is said to be of type integer – “int” must be written in small characters – This is called syntax of a language – Not following it properly leads to syntax errors

19. Data types Floating-point and double –Used for representing non-integer numbers –Examples: float pi, run_rate, Average_score; double e, interestRate; – pi, run_rate, Average_score, e, interestRate are variable names – Notice the comma separating the names

20. Why data types? Why can’t I just use a variable in computation? –Every variable must have a type –Why must it be declared to have a type? –Allocation in the memory –Every variable should get some space in thememory; otherwise how can you use it for computation? –Help the compiler decide how many bits should be reserved for a variable –Observation: compiler must know the data type to size mapping

21. More data types Character and String –Non-numeric variables –You may be surprised: we will see non- numeric variables in computing –Examples: char orange; String something; – orange and something are variable names – Note the syntax – char is used to store a single symbol e.g. ‘f’, ‘2’, ‘$’, ‘ ‘, … – String is used to store a sequence of symbols e.g. “My name is Tintin.”

22. Even more data types Boolean –Can take two values only: true or false –true and false are two boolean constants –You may be surprised to see this type Byte –8-bit integer –Example: byte x; –Range of x? Short –16-bit integer –Example: short y;

23. Constants Integer (int) 1, 234, -56, 0, … Floating-point and double (float, double) 4.5, 56.789, 3.14, 2.71, 0.693, 4.5e3, 45000e-1 Character (char) ‘a’, ‘_’, ‘ ‘, ‘A’, ‘m’, ‘$’, … String (String) “Hi there”, “How are you?”, “This is esc101!!” Boolean (boolean) true, false