String class and STL

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String class and STL
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• string class has the following constructors
• string (const char s) //initialize a string
  object with the string pointed by s
• string(size_type n,char c)
• // create a string object with n element every
  of them char c
• string() creates a default string object of 0
  size

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• string(const char s, size_type n)
• // initialize n byte of string with s
• templateltclass Itergt
• string (Iter begin, Iter end) //initialize a
  string
• // object to the values in the range begin, end)
  , begin and end act like pointer.

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• includeltiostream.hgt
• includeltstringgt
• int main()
• string one(this is test one)
• coutltltoneltltendl
• string two (20,)
• string three(one)
• coutltltthreeltltendl
• oneadd something
• twochange two
• three0P
• string four
• fourtwothree
• coutltltfour
• char s the take some part of string
• string five(s,20)
• string six(s6,s10)
• coutltltsixltltendl

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• char input100
• cingtgtinput
• cin.getline(input,100)
• cin.get(input,100)
• string s
• cingtgts
• getline(cin,s) //read a line, discard \n
• cin.getline(input,100,) // read up to ,
  discard
• getline(cin,stuff,) //read up to , discard
  

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• int main()
• ifstream infile
• infile.open(test.txt)
• if( infile.is_open()false)
• coutltltnot open
• exit(1)
• string item
• int count
• getline(infile,item, )
• while(infile )
• count
• coutltltcountltltltltitemltltendl
• getline(infile,item,)
• infile.close()
• return 0

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• string s1(this is)
• string s2(is this)
• char s320that is
• if( s1 lt s2)
• if(s1s3)
• if(s3 !s2)

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Standard Template Library

• STL provides a collection of templates such as
  containers, iterators and algorithms.
• A container is a unit like an array that can hold
  several values.

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vector template class

• // vector is a container
• include vector
• vector ltintgt v(5) // a vector of 5 int
• int n
• cingtgtn
• vector ltdouble gt scores(n)
• for(int i0 iltni)
• coutltltscoresi

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• vectorltstringgt title(5)
• We can get the size of the vector by size()
• // number of elements
• swap() exchange the contents of two containers
• begin() // return an iterator that refer to the
  first element in a container,
• end() returns an iterator that refers to the last
  element.

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• Iterator is a generalization of a pointer, in
  fact it can be a pointer. It can be an object for
  which operations such as , -- has been defined.
  
• Each container class defines a iterator.
• vector ltdoublegt iterator pd
• // pd an iterator
• vector ltdoublegt scores
• pd scores.begin()
• pd22.3
• pd

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• push_back()
• Add an element to the of a vector, and increase
  vector size.
• vectorltdoublegt scores
• double temp
• while( cin gtgt temp temp gt0)
• scores.push_back(temp)

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• erase() // remove a given range of a vector.
• scores.erase(scores.begin(), scores.begin()2)
• insert() takes three arguments
• //first give the position of which new elements
  are to be inserted.
• vectorltintgt old
• vectorltintgt new

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• old.insert(old.begin(),new.begin()1,new.end())
• More methods
• for_each(), random_shuffle(), sort()
• For_each() // can be used with any container
  class.
• It takes three argumnet, the first two are
  iterators defining the range and the third one in
  a pointer to a function.

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• vector ltTgt V iterator pr
• for( pr V.begin() pr !V.end() pr)
• show(pr)
• for_each( V.begin(), V.end(), show)
• //the function must NOT alter the element of the
  vector

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• The randon_shuffle() function takes two iterators
  that specify a range and rearrange the element in
  that range in the random order.
• Random_shuffle(V.begin(), V.end())
• vectorltintgt s
• sort(s.begin(), s.end()) // it sorts in
  non-decreasing order.
• If the container elements are user-defined
  objects, then we should have an opeatorlt()
  function.

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• struct R
• string title
• int rate
• bool operatorlt ( const R r1, const R r2)
• if( r1.title lt r2.title )
• return
• else if( r1.title r2.title r1.rate lt
  r2.rate)
• return true
• else
• return false
• vector lt Rgt book
• sort(book.begin(), book.end())