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CS201 Lecture No 1 Video

CS 201 Lecture 1



  Lecture Handout 
  Introduction to programming
  Lecture No. 1
   Summary
  o  What is programming
  o  Why programming is important
  o  What skills are needed
  o  Develop a basic recipe for writing programs
  o  Points to remember
  What is programming
  As this course is titled “Introduction to programming”, therefore it is most essential and
  appropriate to understand what programming really means. Let us first see a widely
  known definition of programming. 
  Definition: "A program is a precise sequence of steps to solve a particular problem.”
  It means that when we say that we have a program, it actually mean that we know about a
  complete set activities to be performed in a particular order. The purpose of these
  activities is to solve a given problem.
  Alan Perlis, a professor at Yale University, says: 
  "It goes against the grain of modern education to teach children to program. What fun is
  there in making plans, acquiring discipline in organizing thoughts, devoting attention to
  detail and learning to be self-critical? " 
  It is a sarcastic statement about modern education, and it means that the modern
  education is not developing critical skills like planning, organizing and paying attention
  to detail. Practically, in our day to day lives we are constantly planning, organizing and
  paying attention to fine details (if we want our plans to succeed). And it is also fun to do
  these activities. For example, for a picnic trip we plan where to go, what to wear, what to
  take for lunch, organize travel details and have a good time while doing so. 
  When we talk about computer programming then as Mr. Steve Summit puts it
  “At its most basic level, programming a computer simply means telling it what to do, and
  this vapid-sounding definition is not even a joke. There are no other truly fundamental
  aspects of computer programming; everything else we talk about will simply be the
  details of a particular, usually artificial, mechanism for telling a computer what to do.
  Sometimes these mechanisms are chosen because they have been found to be convenient
  for programmers (people) to use; other times they have been chosen because they're easy
  for the computer to understand. The first hard thing about programming is to learn,
  become comfortable with, and accept these artificial mechanisms, whether they make
  ``sense'' to you or not. “
  Why Programming is important
  The question most of the people ask is why should we learn to program when there are so
  many application software and code generators available to do the task for us. Well the
  answer is as give by the Matthias Felleisen in the book ‘How to design programs’ 
  “The answer consists of two parts. First, it is indeed true that traditional forms of
  programming are useful for just a few people. But, programming as we the authors
  understand it is useful for everyone: the administrative secretary who uses spreadsheets
  as well as the high-tech programmer. In other words, we have a broader notion of
  programming in mind than the traditional one. We explain our notion in a moment.
  Second, we teach our idea of programming with a technology that is based on the
  principle of minimal intrusion. Hence, our notion of programming teaches problem-
  analysis and problem-solving skills withoutimposing the overhead of traditional
  programming notations and tools.” 
   Hence learning to program is important because it develops analytical and problem
  solving abilities. It is a creative activity and provides us a mean to express abstract ideas.
  Thus programming is fun and is much more than a vocational skill.  By designing
  programs, we learn many skills that are important for all professions.
  Paying attention to detail
  In programming, the details matter. This is a very important skill. A good programmer
  always analyzes the problem statement very carefully and in detail. You should pay
  attention to all the aspects of the problem. You can't be vague. You can't describe your
  program 3/4th of the way, then say, "You know what I mean?'', and have the compiler
  figure out the rest. 
  Furthermore you should pay attention to the calculations involved in the program, its
  flow, and most importantly, the logic of the program. Sometimes, a grammatically correct
  sentence does not make any sense. For example, here is a verse from poem "Through the
  Looking Glass" written by Lewis Carol:
  “Twas brillig, and the slithy toves
  Did gyre and gimble in the wabe “ 
  The grammar is correct but there is no meaning. Similarly, the sentence, "Mr. ABC
  sleeps thirty hours every day", is grammatically correct but it is illogical.
  So it may happen that a program is grammatically correct. It compiles and runs but
  produces incorrect or absurd results and does not solve the problem. It is very important
  to pay attention to the logic of the program. 
  Think about the reusability 
  When ever you are writing a program, always keep in mind that it could be reused at
  some other time. Also, try to write in a way that it can be used to solve some other related
  problem. A classic example of this is: 
  Suppose we have to calculate the area of a given circle. We know the area of a circle is
  (Pi * r2). Now we have written a program which calculates the area of a circle with given
  radius. At some later time we are given a problem to find out the area of a ring. The area
  of the ring can be calculated by subtracting the area of outer circle from the area of the
  inner circle. Hence we can use the program that calculates the area of a circle to calculate
  the area of the ring.
   users know a lot of things, this is a big mistake. So never assume that the user of your

  program is computer literate. Always provide an easy to understand and easy to use
  interface that is self explanatory. 
  Understand the fact that computers are stupid
  Computers are incredibly stupid. They do exactly what you tell them to do: no more, no
  less-- unlike human beings. Computers can't think by themselves. In this sense, they
  differ from human beings. For example, if someone asks you, “What is the time?”, “Time
  please?” or just, “Time?” you understand anyway that he is asking the time but computer
  is different. Instructions to the computer should be explicitly stated. Computer will tell
  you the time only if you ask it in the way you have programmed it. 
  When you're programming, it helps to be able to "think'' as stupidly as the computer does,
  so that you are in the right frame of mind for specifying everything in minute detail, and
  not assuming that the right thing will happen by itself. 
  Comment the code liberally
  Always comment the code liberally. The comment statements do not affect the
  performance of the program as these are ignored by the compiler and do not take any
  memory in the computer. Comments are used to explain the functioning of the programs.
  It helps the other programmers as well as the creator of the program to understand the
  code.
  Program design recipe
  In order to design a program effectively and properly we must have a recipe to follow.  In
  the book name ‘How to design programs’ by Matthias Felleisen.and the co-worker, the
  idea of design recipe has been stated very elegenlty as  
  “Learning to design programs is like learning to play soccer. A player must learn to trap a
  ball, to dribble with a ball, to pass, and to shoot a ball. Once the player knows those basic
  skills, the next goals are to learn to play a position, to play certain strategies, to choose
  among feasible strategies, and, on occasion, to create variations of a strategy because
  none fits. “
  The author then continue to say that: 
  “A programmer is also very much like an architect, a composers, or a writer. They are
  creative people who start with ideas in their heads and blank pieces of paper. They
  conceive of an idea, form a mental outline, and refine it on paper until their writings
  reflect their mental image as much as possible. As they bring their ideas to paper, they
  employ basic drawing, writing, and playing music to express certain style elements of a
  building, to describe a person's character, or to formulate portions of a melody. They can
  practice their trade because they have honed their basic skills for a long time and can use
  them on an instinctive level. 

  Programmers also form outlines, translate them into first designs, and iteratively refine
  them until they truly match the initial idea. Indeed, the best programmers edit and rewrite
  their programs many times until they meet certain aesthetic standards. And just like
  soccer players, architects, composers, or writers, programmers must practice the basic
  skills of their trade for a long time before they can be truly creative. 
  Design recipes are the equivalent of soccer ball handling techniques, writing techniques,
  arrangements, and drawing skills. “
  Hence to design a program properly, we must:
  o  Analyze a problem statement, typically expressed as a word problem.
  o  Express its essence, abstractly and with examples.
  o  Formulate statements and comments in a precise language.
  o  Evaluate and revise the activities in light of checks and tests and
  o  Pay attention to detail.
  All of these are activities that are useful, not only for a programmer but also for a
  businessman, a lawyer, a journalist, a scientist, an engineer, and many others.
  Let us take an example to demonstrate the use of design recipe:
  Suppose we have to develop a payroll system of a company. The company has permanent
  staff, contractual staff, hourly based employees and per unit making employees.
  Moreover, there are different deductions and benefits for permanent employees and there
  is a bonus for per unit making employees and overtime for contractual employees. 
  We need to analyze the above problem statement. The company has four categories of
  employees; i.e.; Permanent staff, Contractual staff, hourly based employees and per unit
  making employees. Further, permanent staff has benefits and deductions depending upon
  their designation. Bonus will be given to per unit making employees if they make more
  than 10 pieces a day. Contractual employee will get overtime if they stay after office
  hours.
  Now divide the problem into small segments and calculations. Also include examples in
  all segments. In this problem, we should take an employee with his details from each
  category. Let’s say, Mr. Ahmad is a permanent employee working as Finance Manager.
  His salary is Rs.20000 and benefits of medical, car allowance and house rent are Rs.4000
  and there is a deduction of Rs.1200. Similarly, we should consider employees from other
  categories. This will help us in checking and testing the program later on. 
   The next step is to formulate these statements in a precise language, i.e. we can use the
  pseudo code and flowcharting. which will be then used to develop the program using
  computer language.
  Then the program should be evaluated by testing and checking. If there are some changes
  identified, we revise the activities and repeat the process. Thus repeating the cycle, we
  achieve a refined solution.