Compe260

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Lecture 4

• Compe260

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Char data Type

• Memory requirements
• 1 byte 8 bits
• Permitted Operations
• Same as signed integer
• Char variable assignments may be
• Numeric
• represents integers from -128 to 127, negative
  numbers are stored using 2s complement notation.
• char cVar 0x30
• If a char is to be used numerically, use a
  typedef
• typedef char INT8
• INT8 cVar 0x30 //this is clear
• ASCII
• char cVar 0 //stores ASCII code for 0
  (0x30)
• Strings are arrays (consecutive sequence) of
  characters where the last character of the string
  is an ASCII NULL
• char myString this is a string declaration
  //allocates and initializes 29 bytes of // memory
  for the string
• Char myString a, b, c, 0

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unsigned char data Type

• Memory requirements
• 1 byte 8 bits
• Permitted Operations
• Same as unsigned integer
• Char variable assignments may be
• Numeric
• represents integers from 0 to 255.
• unsigned char ucVar 0x30
• If an unsigned char is to be used numerically,
  use a typedef
• typedef unsigned char UINT8
• UINT8 ucVar 0x30 //this is clear

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sizeof operator

• Returns the number of bytes of storage required
  to hold a variable of a given type.
• sizeof(int) returns the number of bytes required
  to store an int.
• All memory is allocated in multiples of bytes.
• Bits 2Bytes
• Bytes log2(bits)
• For unsigned integer (char, short, long) types
• Maximum value is 2Bits 1
• Range of values 0 lt x lt 2Bits 1

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Arrays

• An array is a collection of data of the same
  type.
• Values in the collection can be operated on using
  index or pointer notation.
• Name of the array is a pointer to the first
  element of the array.
• UINT16 myVar10 //allocates 10 2 bytes of
  memory
• myVar is the same myVar0
• Index notation is clearer and recommended.
• Memory Requirements
• Number of array elements sizeof(data type)
• Permitted operations
• Programmer may manipulate each element using
  operations defined for the underlying data type.

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Pointers

• Pointers store the address of a variable.
  Pointers access the contents of a variable
  indirectly by reference.
• Indirection
• Memory Requirements
• The size of an address for a particular
  processor.
• Use sizeof operator to determine exactly.
• Operations
• Arithmetic , , -, --, etc
• Numbers refer to the size of the underlying data
  type.
• Danger do use an unassigned pointer
• Interesting fact
• A pointer can be used as the base pointer of an
  array.
• int myIntPtr, intArray10, myInt
• myIntPtr intArray3 //assign the pointer to
  reference the 4th element
• myInt myIntPtr0 //store value of 4th element
  of the array in myInt