CIS 403503 Accelerated DataFile Structures

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CIS 403/503Accelerated Data-File Structures

• Lecture 1
• C Types and Control

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Objectives

• In this lecture, you will learn to
• Write a simple C program
• Use preprocessor and using directive
• Display output to terminal
• Define data with different types
• Understand the syntactic difference between C
  and Java
• Use typecasting and typedef

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C vs. Java

• High level differences
• Compiled vs. interpreted
• Security and robustness
• Multithreading
• API Differences

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Reasons to Use C

• Templates
• Operator overloading
• STL
• Resource reclamation
• Conditional compilation
• Accessor and mutator
• Multiple inheritance
• Space efficiency

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First C Program
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First Program

• include ltiostreamgt
• using namespace std
• int main()
• cout ltlt Hello World! ltlt endl
• return 0

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main Function

• Control starts
• Declared in global scope
• Return type int
• Parameters for command-line arguments

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Preprocessor

• Lines beginning with are preprocessor
  directives
• include directive has the compiler insert
  source code from a system file, e.g. iostream or
  user-defined file

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The using Directive

• Is equivalent to import in Java
• namespace is the C equivalent of packages

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Output

• cout is the standard output stream
• ltlt is the overloaded output operator
• What about input?

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Basic Types
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Integer

• 16, 32, 64 bits, platform dependent
• short/long, e.g. 10L
• signed/unsigned, e.g. 10U
• signed char

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Floating Point

• float
• double

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Character

• 16bit unicode in Java, but no size specified in
  C standard
• Signed or unsigned by default is unspecified.
• Char constant is enclosed in
• Escape sequence for unprintable characters

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Boolean

• bool true/false
• Not originally part of C
• Legal erroneous code

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Enumerated Types

• Defined by providing a range of constant values,
  e.g.
• enum weekdays Monday, Tuesday, Wednesday,
  Thursday, Friday, Saturday, Sunday
• Declaration of weekdays is as follows
• weekdays workDays, VacationDays

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local and global

• Variables that declared outside of any function
  are called global
• Accessible within all subsequent functions
• Variables that are declared inside a function are
  local
• Accessible within the bounds of the function
• Or local to the body of a control structure

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Arrays

• A fixed-size set of same type values
• Legal subscripts range from 0 to n - 1
• The language does not check on the subscript
  index values
• e.g.
• int temp12
• double matrix1020
• string dayNames7 Monday, Tuesday,
  Wednesday, Thursday, Friday, Saturday,
  Sunday

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Structures

• A collection of fields of mixed data types
• Represent data associated with a common subject
• struct person
• string name
• int age
• enum M, F gender

person me me.name zhou
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Functions and Parameter Passing
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Function Definition

• C allows non-member functions.
• Return type
• Function name
• Parameter list
• body

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Example 1

• int bigger ( int a, int b)
• return a gt b ? a b

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Example 2

• Compute the sum of the array elements
• int aSum(int a, int n)
• int sum 0
• for ( int i 0 i lt n i)
• sum ai
• return sum

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Local Variables

• Local variables become active when function
  begins execution, disappear when the function
  finishes execution
• A run-time stack is maintained for local
  variables
• If function A invoke B, B must terminate before A
  resumes

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Invocation

• Provide arguments with types compatible with
  formal parameters
• Pass-by-value
• A copy of arguments is created
• Actual argument values can not be changed
• Pass-by-reference
• A reference to the actual arguments is created
• Argument values can be changed

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Pass-by-Value

• include ltiostreamgt
• using namespace std
• void swap ( int a, int b)
• int tmp a
• a b
• b tmp
• int main()
• int x 1
• int y 2
• swap (x,y)
• cout ltlt x ltlt x ltlt y ltlt y ltlt endl
• return 0

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Pass-by-Reference

• include ltiostreamgt
• using namespace std
• void swap ( int a, int b)
• int tmp a
• a b
• b tmp
• int main()
• int x 1
• int y 2
• swap (x,y)
• cout ltlt x ltlt x ltlt y ltlt y ltlt endl
• return 0

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Declaration

• In C, function must be defined before the
  invocation.
• Or use prototype to declare functions earlier.
• Not include body
• Terminate with a semicolon.

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Example

• include ltiostreamgt
• using namespace std
• int bigger( int a, int b) // function
  declaration
• int main()
• int x 1
• int y 2
• cout ltlt bigger(x,y) ltlt is bigger ltlt endl
• return 0
• int bigger ( int a, int b)
• return a gt b ? a b

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Default Parameter

• Specify default values for a formal parameter in
  the function definition.
• All the subsequent parameters must have default
  values too.
• Default values cannot be specified in both
  definition and declaration.
• Good practice in the declaration

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Example

• int power (int b, int e 2)
• Legal invocation
• power(3) //return 9
• power(3,3) //return 27
• What about
• int power (int e 2, int b)
• Possible ambiguity
• int power (int b, int e 2)
• int power (int b)

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C vs. JavaSyntactic Differences
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Operators and Expressions

• Java has well-defined semantics, whereas c code
  can be implementation dependant.

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Case 1

• int x 5
• x x
• In java, what is x?
• In C?

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Case 2

• 8/-5 ?
• In Java, integer division rounds down
• In C, rounds down or rounds to the nearest

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Case 3

• C supports comma operator
• Take two expressions, evaluate to the second
  expression. e.g. 2,5 evaluates to 5
• Cause erroneous code 3.14 or 3,14
• pow((3,4))?

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Case 4

• In Java, gtgtgt unsigned right shift, gtgt signed
  right shift
• In C, only gtgt, depends on whether the left
  operand is signed or unsigned

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Conditional Structures

• if statement in C is identical to Java.
  However, in C the condition can be either an
  int or a bool
• Cause legal erroneous code
• if (x 0)
• Historically, C interprets 0 as false and
  nonzero as true

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Loops

• C supports the for, while, and do loop with
  break and continue statements.
• C does not allow labeled break and labeled
  continue

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switch

• Used to select one alternative out of many
• Switch value must be integer, char or enumerated
  value
• default can be used to issue default operations
  for non-matched values

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Example

• switch(aDay)
• case Monday
• efficiency low
• case Tuesday
• efficiency normal
• case Wednesday
• efficiency high
• default
• efficiency normal

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Definite Assignment

• Java makes sure every local variable has been
  assigned a value
• C compilers are not required to check definite
  assignment
• Note it wont take long till you encounter
  runtime error caused by uninitialized variables.

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Other Syntax in C

• Typecast
• typedef statement

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Typecast

• C is more liberal
• double z
• int x 6
• int y 10
• z x/y
• What is z?

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typedef

• Allow C programmer to assign meaningful names
  to existing types.
• typedef short SMALLINT
• typedef int BIGINT
• SMALLINT i
• BIGINT loop_count

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Things to Remember

• Controls start at main
• Lines beginning with are preprocessor
  directives
• include inserts source code from other files
• Output to terminal cout ltlt
• Primitive types are short, int, long, char
  (signed or unsigned)

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Things to Remember

• In C, zero represents false, non-zero is true.
• C allows comma operator.
• C does not support labeled break and continue.
• C does not check definite assignment.
• typedef may be used to replace existing types.
  

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Possible Quiz Questions

• What is include directive for?
• What is the purpose of using?
• Write a simple C program.
• Use control structures if, loops. Pay attention
  to the true/false condition.
• Difference between pass-by-value and
  pass-by-reference
• Use typedef to replace an existing data type