Chapter 1 Arrays, Pointers, and Structures

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Chapter 1Arrays, Pointers, and Structures

• Saurav Karmakar
• Spring 2007

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Syntax vs. Semantics

• Syntax the form of the presentation
• Semantics the meaning of the presention

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1.1 What are Arrays, Pointers, and Structures

• Pointers store an address. Used to access
  objects
• Aggregate collection of objects stored in one
  unit.
• Arrays indexed collections of identical-type
  objects. (aggregate)
• Structures collections of objects that need not
  be of the same type. (aggregate)

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1.2 Arrays and Strings

• Arrays indexed collections of identical-type
  objects.
• Array index always start on 0
• Arrays can be used in two different ways
  primitive arrays and vectors.
• First class object (vectors) vs. second class
  object (arrays)

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First class object (vectors) vs. second class
object (arrays)

• First class object (vectors, string class) can
  be manipulate in all the usual ways.
• second class object (arrays) can be manipulate
  in only certain restricted ways.

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Vectors

• include ltvectorgt
• Declaration vectorlttypegtidentifiers(size)
• Example vectorltintgt a(3)
• Vector can be indexed as an array, using

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Vectors

• Vector member functions
• vectorltintgt v(10)
• v.at() // equal
  to v
• v.size() // return
  the number of elements in v
• v.front() // return
  the first element in v
• v.back() // return the
  last element in v
• v.clear() // delete
  all the element in v
• v.empty() // return 1 if
  v is empty else return 0

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Vectors

• v.resize( val ) // change size of v
  to val
• v.pop_back() // remove the last
  element in v
• v.push_back( val ) // appends val to the
  end of v
• v.capacity() // return the number
  of element that
• vector
  can hold before it will need to
• 
  allocate more space
• http//www.cppreference.com/cppvector/all.html

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How to do Vectors resize

• Example
• vectorltintgt arr(10)
• arr.resize(12)

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Function calls

• Call by value The actual argument is copied into
  the parameter
• ex int findMax(vectorltintgt a)
• Call by reference avoids copy, it allows change
  of the parameter
• int findMax(vectorltintgt a)

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Function calls

• Call by constant reference avoids copy and
  guarantees that actual parameter will not be
  change
• ex. int findMax(const vectorltintgt a)

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Multidimensional Array

• Second class object
• First class equivalent is matrix
• Syntax matrixltintgt x(2,3)

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Strings

• includeltstringgt
• string sHello World!
• Int sizes.length()
• coutltlt s4 ltltendl // resulto
• coutltlt s ltltendl

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1.3 Pointers syntax in C

• How to Declare a pointer
• int ptr
• unary operator that returns the address of
  the object, it is placed before.
• int x5
• int ptr
• ptrx
• cout ltlt ptr ltlt endl // output 0013FF7C

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Pointer cont.

• unary deferencing operator which can access
  data/object being pointed.
• ptr 10
• Example
• int x5
• int ptrx //ptr5 ptr 0013FF7C
• ptr10 //ptrx10
• Illegal ptrx //x is not an address

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Legal Pointer Syntax

• int x10
• Declare a pointer
• int ptrx or int ptr
• ptrx
• After declare
• ptr15

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Illegal Pointer Syntax

• int ptr //run time error
• ptrx
• ptrx or int ptrx

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Pointer

• ptr x // Symantically incorrect
• What happens bellow ?
• int x5
• int ptr x
• ptr 1
• ptr

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Pointers

• What happens bellow ?
• type ptr1, ptr2
• ptr1ptr2
• ptr1ptr2
• C is strongly typed language.

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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, an operator delete must be
  applied to the object, through its pointer, to
  avoid memory leakage

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Cont.

• Example
• string str_ptr
• str_ptr new string("Hello")
• coutltlt str_ptr ltlt endl //Hellow
• coutltlt (str_ptr).length() ltltendl //5
• delete str_ptr

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Stale pointer double delete

• string s new string(hello)
• string ts
• delete t

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1.5 Reference variables

• Reference type is an alias and may be viewed as a
  pointer constant that is always dereferenced
  implicitly.
• Reference variables must be initialized at
  declaration time.
• Viz. int l0
• int c l
• c s // Not allowed

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Cont.

• includeltiostreamgt
• using namespace std
• void swap_wrong (int a, int b)
• int tempa ab btemp
• void swap_c (int a, int b)
• int tempa ab btemp
• void swap_ref (int a, int b)
• int tempa ab btemp
• void main()
• int x5,y7
• swap_wrong(x,y) // x5, y7
• swap_c(x,y) // x7, y5
• swap_ref(x,y) // x5, y7

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Structures

• Structures collections of objects that need not
  be of the same type.
• Syntax
• struct identifier

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Structures

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

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Structure Data

• Indigenous data are completely contained by the
  structure.
• Exogenous data reside outside the structure and
  are accessed through a pointer.

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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
• , , . , -gt