CIS 17 C Programming

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CIS 17 - C Programming
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Lecture 13

• Command-Line Arguments
• Additional Features
• Bitwise Operators
• Macros
• Multi-file programming
• Abstraction
• Reusable code
• Conditional Compilation

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Command-Line Arguments

• Passing Arguments to Main()
• Up to now we have used redirection to enter data
  into our programs lt
• We will now pass data directly to the program
  using the command line
• C\powerc\my_program.exe arg1 arg2 arg3

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Command-Line Arguments

• Information on the command line is stored in
  memory.
• Each string terminates with a \0 character
• Main() is only allowed to receive 2 arguments,
  they must be part of the function declaration.
• int argc The number of arguments
• argv Table of addresses

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Command-Line Arguments

• If you would like to receive information from the
  command line you must declare your main() with
  these arguments
• void main(int argc, char argv)
• This will take as many arguments as you can fit
  on a line.
• my_prog.exe in_file out_file1.txt err_file.txt

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Additional Features Cont.

• Conditional Expressions - ?
• Alternate way of expressing simple if-else
• exp1 ? exp2 exp3
• If the values of exp1 is true exp2 is evaluated
  otherwise exp3 is evaluated
• Rate (hours gt 40) ? 0.045 0.02

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Additional Features Cont.

• The goto Statement
• Provides an unconditional transfer of control to
  some other statement in a program
• goto err
• err printf(blah blah)
• Dont use them!!!!

8
Bitwise Operators

• , , , , ltlt, gtgt
• Used to perform bit operations
• AND Operator -
• Performs bit by bit and comparison
• 1 0 1 1 0 0 1 1
• 1 1 0 1 0 1 0 1
• 1 0 0 1 0 0 0 1
• Rule The results of an AND operation is a 1 if
  one when both bits being compared is a 1s,
  otherwise the result is 0.

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Bitwise Operators Cont.

• Inclusive OR Operator -
• Performs a bit-by-bit comparison
• 1 0 1 1 0 0 1 1
• 1 1 0 1 0 1 0 1
• 1 1 1 1 0 1 1 1
• Rule The results of an OR operation is a 1 if
  either of the bits being compared is a 1,
  otherwise the result is 0

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Bitwise Operators Cont.

• Exclusive OR Operator -
• Performs a bit-by-bit comparison
• 1 0 1 1 0 0 1 1
• 1 1 0 1 0 1 0 1
• 0 1 1 0 0 1 1 0
• Rule The results of an XOR operations is a 1 if
  one and only one of the bits being compared is a
  1, otherwise the result is 0

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Bitwise Operators Cont.

• Complement Operator -
• Performs a bit-by-bit switch
• 1 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0
• Rule The results of a complement operation is to
  change ones to zeros and zeros to ones.

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Bitwise Operators Cont.

• Shift operators
• ltlt causes the bits in an operand to be shifted to
  the left by a given mount.
• gtgt causes the bits in an operand to be shifted to
  the right by a given amount.
• op1 op2 ltlt 4
• Shifts op2 to the left and stores it in op1

13
Macros

• The direct inline expansion of one word into
  many.
• define FORMAT The answer is f\n
• Enables us to write
• printf(FORMAT, 15.2)

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Macros

• Other macro examples
• define SQUARE(x) x x
• Can be used with any data type argument
• Use \ to continue on a new line

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Multi file programming

• Personal Libraries
• Header files
• Implementation

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Abstraction

• The process of separating the inherent qualities
  or properties of something from the object that
  they belong
• Procedural abstraction
• separate the concern of what is to be achieved by
  a function from the detail of how it is to be
  achieved.
• Break down the program into solvable chunks

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Abstraction

• Data abstraction
• Specify data objects and operations to be
  performed on these objects.
• A logical view of data object as opposed to its
  physical view
• Information hiding
• Data can only be accessed using operators
• Protects implementation details of the lower
  level functions

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Reusable Code

• Encapsulation
• Packaging data and operators in to a library
• Standard library modules
• Stack
• Queue
• Hide the internal details from the programmer
• Programmer uses the tools provided in the package

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Conditional Compilation

• Programmer selective compile method
• define TRACE (turns on statements)
• if defined (TRACE)
• printf(This will be printed if trace is
  defined)
• endif