CS 110

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CS 110

• Introduction to Computer Programming

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Instructor

• Name Vana Doufexi
• Office 2-229 Ford Building
• Email vdoufexi_at_cs.northwestern.edu
• Office phone [phone]
• Office hours By appointment.

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Resources

• Class webpage http//www.cs.northwestern.edu/aca
  demics/courses/110
• Use to
• read important announcements
• read about class policies
• look up your grades
• download homework handouts
• download class notes
• access helpful tutorials
• access the discussion forum (provided by
  Blackboard)

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Resources

• Discussion Forum
• Use to
• discuss class material
• ask questions on the material or the assignments
  (but NEVER post solutions)
• share solutions to posted practice problems
• get hints and tips for the assignments.

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What is a computer?

• A device that can
• accept data (input),
• manipulate it (process) according to specific
  instructions
• generate results (output) as a result of the
  processing.
• (optional) store the results

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What is programming?

• Program a sequence of human-readable
  instructions telling a computer how to do a
  particular task or solve a given problem.
• Programming Designing, writing and testing a
  computer program.

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The programming process

• Analyze Find the core problem
• Decide the inputs and outputs
• Decide how to go from the inputs to the outputs
  (only the process, not detailed mechanics)
• Break it down into sub-problems.
• This part is completed on paper.
• The end result is usually a flow-chart or
  pseudocode.

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The programming process

• Implement
• Write instructions
• Tackle each sub-problem separately by writing a
  set of instructions (a function) for it.
• The computer can only understand instructions
  written in machine language (sequences of 1s and
  0s).
• In order to make the programming process easier
  for humans, researchers developed new, easier
  (for humans) to understand languages as well as
  special tools that could convert programs written
  in human-readable languages into programs written
  in machine language.
• C is an example of such a language.

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The programming process

• Implement
• Write instructions (continued)
• Some operations that we may need our program to
  perform are so common (e.g. reading input from
  the keyboard) that it would be expedient to have
  a ready module for it.
• A collection of such modules is called a library.
  For example, the Input/Output library contains
  modules (functions) that can be invoked to read
  input from the keyboard, or write output to the
  screen, etc.
• A library function may be invoked from within a
  program.

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The programming process

• Implement
• Compile your program
• The compiler is the tool that translates a
  program written in a high-level language such as
  C into a program written in machine language.
• The first step in the compilation process is
  called preprocessing. The preprocessor scans the
  input program for special instructions called
  preprocessor directives.
• These directives tell the preprocessor to do
  things such as include an already existing
  library into the program.

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The programming process

• Implement
• Compile your program (continued)
• The second step in the compilation process is the
  actual translation.
• The compiler tries to figure out whether the
  program satisfies the rules of the language. A
  good compiler will catch several types of
  mistakes and give informative descriptions and
  suggestions to the programmer.
• One type of mistake is a syntax error. For
  example, a missing parenthesis in an arithmetic
  expression. Such mistakes are generally easy for
  the compiler to identify.

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The programming process

• Implement
• Link your program
• Once a program has been compiled successfully, a
  tool called a linker is used to combine all its
  components together and generate an executable
  program.
• Execute (run) your program
• In order to run your program, you use an
  operating system command to load it into your
  computer's memory and execute its (machine
  language) instructions one at a time.

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The programming process

• Test and debug
• A program that compiles and executes successfully
  does not necessarily work as expected.
• It is very important to test the program with
  several kinds of inputs to make sure that it
  always gives the expected outcome.
• Programs often contain a type of error called a
  bug (or, more formally, a logic or design error).
  Such errors are hard to find and sometimes are
  not found until long after a program has been
  released.
• A tool called the debugger is very helpful in
  finding such errors.

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The programming process

• Test and debug
• The recommended way to test a program is one
  module at a time.
• Once all modules have been tested successfully,
  start combining them a few at a time and test
  again.
• This way, it is easier to identify where
  potential errors are.

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The programming environment

• The Visual Studio environment
• This application encompasses almost all of the
  tools that you will need for the programming
  process
• a text editor to write the program
• a compiler
• a linker
• a loader to load the program into memory so that
  it can be executed
• a debugger

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How to program example

• Write a program that computes the square footage
  of a house, given the dimensions of each room.
• Step 1
• Input
• The number of rooms (an integer)
• The dimensions of each room in feet (real
  numbers)
• Output
• The square footage of the house in square feet
  (real number)
• Subproblems
• compute the area of a room
• add up the areas of all rooms

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How to program example

• Write a program that computes the square footage
  of a house, given the dimensions of each room.
• Step 2
• Translate your instructions into C language.
• We will learn how by exploring variables, types,
  statements, expressions, assignments,
  conditionals, loop constructs, functions, etc.
• Compile your code
• The compiler is a program that converts the
  human-readable instructions that you wrote into
  machine-executable instructions.

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How to program example

• Write a program that computes the square footage
  of a house, given the dimensions of each room.
• Step 3
• Test Debug your program
• There are two types of mistakes
• syntax mistakes (easy to fix compiler helps)
• design mistakes, a.k.a. bugs (often hard to find
  debugger helps).
• Test your program to make sure it works correctly
  and can handle situations such as erroneous input
  (what if someone types in negative dimensions?)