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CS 101 Oct. 5

• Computer problem solving
• Chapter 6 read pp. 148-174
• Problem-solving procedure
• Structure of a solution
• Examples!

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Review what is CS ?

• The study of how we
• Solve problems
• Represent information
• In problem solving, wed like
• Find systematic ways of going about solution
• Correct, quick and informative solutions.
• Information can be
• Different types numbers, text, images, sound,
  the software itself
• The input and output to a computer program

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Why create software?

• Computational power
• Excel is limited to so many rows/columns
• Can convert data to images
• Can create games and useful applications
• With one language, can solve virtually any
  problem.
• Built-in features of languages
• Many common calculations are pre-defined for you
  such as sorting, opening files, surfing the Web,
  creating a button, etc.

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Software

• Powerful!
• We get to tell the machine exactly what we want.
• Sometimes, existing programs like Excel or
  Photoshop are not enough.
• Program sequence of instructions for CPU to
  obey.
• Works like a recipe.
• A recipe has ingredients, steps, and result is
  food!
• A program has input, calculations, output. ?
• When we start to look at programs, be on the
  lookout for these 3 parts.

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Recipes

• Cooking may be a good analogy, because its
  solving a specific problem Im hungry. ?
• What do we see in recipes? Heres one
• Brown the beef 15 min. Drain grease.
• Dice carrot, celery, onion (aka mirepoix)
• Cut up and boil 6 potatoes until soft.
• Mash potatoes
• Add flour, spices, sauce, mirepoix to beef.
• Put meat mixture into casserole, top with
  potatoes.
• Bake in oven at 400 for 30 minutes.

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Recipes (2)

• A computer program has some of the same elements
  as a recipe
• In recipes we see
• Ingredients (the nouns of the problem)
• Steps to perform (the verbs)
• In some steps, we continue/wait for something
• Although its not obvious, sometimes we check
  things
• Are potatoes fully mashed?
• Should I add more _____ to the mixture?

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Recipes (3)

• But we dont eat the same stuff every day. Once
  we know a few recipes, we can put together a menu
  for choices.
• if (have all ingredients), make Shepherds pie.
• if (no potatoes), just make soup instead.
• if (no veggies), make hamburger.
• if (no beef), make pasta.
• When you view a whole menu as a program, then
  making soup becomes a sub-program.
• A large program is composed of several parts.
• In industry, sometimes each part implemented by
  different people. A kitchen may have many chefs.

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Problem-solving

• Understand problem inputs and outputs
• Write solution in English pseudocode
• Write code in a programming language
• Compile
• Run and test
• When program works, can refine.

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Problems

• The earliest problems given to a computer were
  mathematical.
• Sometimes there is no clean formula
• Many equations cant be solved analytically. For
  example, cos(x) x. Need to solve numerically.
• Ex. Heat equation is a partial differential
  equation (PDE). Most PDEs have to be solved
  numerically.
• Ex. Calculating a square root.
• And even if there is a clean formula, a computer
  can help you automate the calculations.

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Problems (2)

• Mathematical problems may at first sound
  boring. But they include many useful
  applications
• Ex. Finding directions
• Other kinds of problems for the computer
• Games
• Record keeping, managing investments,
• Networking, communication
• Multimedia (e.g. image processing)
• Of course, much more!