Chapter 1 Arrays, Pointers, and Structures

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Chapter 1Arrays, Pointers, and Structures

• Ken Nguyen
• Spring 2002

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1.1 What are arrays

• Aggregate collection of objects stored in one
  unit
• Arrays indexed collections of identical-type
  objects.
• Pointers objects are used to access other
  objects.
• Structures collections of objects that need not
  be of the same type.

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1.2 Arrays and Strings

• Arrays can be used in two different ways
  primitive arrays and vectors.
• String in C is implemented in both structures.
• First class object(vectors) vs. second class
  object (arrays)

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Vectors

• include ltvectorgt
• Declaration vectorlttypegt identifiers(size)
• Example vectorltintgt a(3)
• Vector can be indexed as an array, using
• Vector member functions size, resize, push_back,
  pop_back, . . .

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Function calls

• Call by value
• int findMax(vectorltintgt a)
• Call be reference
• int findMax(vectorltintgt a)
• int findMax(const vectorltintgt a)

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Arrays

• int a2 0,1
• // multidimensional arrays
• int b22 1,1, 2,2
• matrixltintgt x(2,3)

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Strings

• include ltstringgt
• string s hello world!
• int size s.length()
• s.c_str() returns a \0 terminated primitive
  character array.

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1.3 Pointers syntax in C

• unary operator that returns the address of
  the object.
• Type identifier // pointer declaration
• int a 3
• int iPtr
• iPtr a // points iPtr to the memory
  address of variable a.
• iPtr 5 // what is the value of a ???(5)

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Pointers Cont

• Precedence rules applied on pointer arithmetic
• int a 10
• int ptr a
• ptr 1 // ptr
• ptr // returns 11, and //adv. ptr to
  the next //memory slot

a
10
ptr
11
ptr
ptr
11
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1.4 Dynamic memory management

• new operator allocates memory and returns a
  pointer to the newly created object.
• When an object that is allocated by new is no
  longer referenced, applied delete operator on
  this object, through its pointer, to avoid
  memory leakage

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Figure1.10

• include ltiostreamgt
• include ltstringgt
• using namespace std
• int main()
• string strPtr
• strPtr new string(hello)
• coutltlt The string is ltlt strPtrltltendl
• delete strPtr
• return 0

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Dangling/stale pointers

• string s new string(hello)
• string t s // t s point to the same block
• delete t // s become invalid //gtstale/dang
  ling pointer
• delete s // another problemgtdouble
  //deletion
• string oop() string s oop return s
• cout ltltoop()ltltendl // run time error

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1.5 Reference variables

• int long_name 0
• int cnt long_name //cnt is an alias
• cnt 3 // long_name 0

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Differences between ref. and pointers

• void swapPtr(int a, int b)
• int tmp a
• a b
• b tmp
• int x 3, y 5
• swapPtr(x, y) // call-by pointer

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• void swapRef(int a, int b)
• int tmp a
• a b
• b tmp
• int x 3, y 5
• swapRef(x, y) // call-by reference
• References are implicitly dereferenced

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Structures

• Struct Student
• string firstName
• string lastName
• Student a, sPtr // declaring Student
• a.firstName Mary//accessing member data
• sPtr a
• (sPtr).lastName Smith
• //sPtr-gtlastName Smith // same as above

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Copying objects

• Shallow copy a copy of pointers rather than data
  being pointed at
• Deep copy a copy of data being pointed at rather
  than the pointers.

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Summary

• Vectors vs. arrays
• First class objects vs. second class objects
• Ways to pass data to functions
• Pointers
• Dynamic memory allocation deallocation
• and . Operators -gt