STL of c++ Algorithms,Iterator’s,Container’s class’s

in reality, the standard template library (STL )   is a collection of C++ template  classes for data structures and algorithms

in brief, It is impossible to learn c++ (STL) without proper working knowledge  of data structure  and algorithms

without a doubt, a novice has to learn first DSA and algorithms  to study STL in C++

During competitive programming time is a valuable asset  at this instant,

it is important to realize, you can use STL  to overcome the problem of writing function again and again

thus, STL library has three components

1. Algorithm’s
2. Container’s
3. Iterator’s

Algorithms

in a word, there are build in algorithms available in STL C++

such as: sort(); set_union(); binary_search(); sort_heap(); push_heap(); pop_heap(); make_heap(); merge_heap(); reverse(); copy();

Example of  a sort algorithm in STL

#include <iostream>
#include <algorithm>
using namespace std;
void show(int A[])
{
    for(int i = 0; i < 8; i++)
        cout << A[i] << " ";
}
int main()
{
    int A[8]= {1, 5, 6, 7, 3, 4, 2, 0};
    sort(A, A+8);//sort algorithm
    show(A);
    return 0;
}

Output

0 1 2 3 4 5 6 7

Iterator’s

on the positive side, Iterator’s are available in every collection

First method

vector<int>:: iterator itr;
    for(itr=v.begin();itr!=v.end();itr++)
        cout<<*itr<<endl;

Second  method

for(int x:v)
        cout<<x<<endl;

Container’s class’s

such as : vector, forward_list, list,

deque,priority_queue, stack,

set, multiset

Vector class contain a different types of member functions

that is : push_back(), pop_back(), insert(), remove(), size(), empty()

#include <iostream>
#include <vector>
using namespace std;
int main()
{
    //Vector of type integer
//V is an object and it is initialized with 1,2,3,4,5
    vector<int> v ={1,2,3,4,5};
    v.push_back(6); //Push_back member function of vector class
    v.push_back(7);
    //iterator class belong to a vector class
    //itr is an object of iterator
    vector<int>::iterator itr;
    cout<<"First iterator  method" << endl;
    for(itr=v.begin();itr!=v.end();itr++) //First iterator  method
        cout<<*itr<<endl;
    cout<<"Second  iterator by each loop method"<<endl;
    for(int x:v)//Second  iterator by each loop method
    cout <<x<<endl;
    return 0;
}

Output

First iterator  method
1 2 3 4 5 6 7
Second  iterator by each loop method
1 2 3 4 5 6 7

vector class

#include <iostream>
#include <vector>
using namespace std;
int main()
{
    vector<int> v={1,2,3,4,5,6,7};
    v.push_back(8);
    v.push_back(9);
    for(int x:v)
        cout<<x<<endl;
    return 0;
}

Output

1 2 3 4 5 6 7 8 9

vector member function’s

string class

that is to say, in C++ you declare string as

string  str;

for instance, in C you declare string as

char str[40];

The operators that you can use on a string

Using  assignment(=),  concatenation(+), insertion(>>), extraction (>>) operators

#include <iostream>
#include<string>

using namespace std;
int main()
{
    string s; //string class with object  S
    s ="hi "; // assignment(=) operator
    string s1=" there";
    string s2;
    s2 = s+s1; // concatenation(+) operator
    cout << s2; // insertion (>>) operator
    return 0;
}

Output

hi there

Using Concatenation assignment (+=) operator  on a string

#include <iostream>
#include<string>

using namespace std;
int main()
{
    string s; //string class with object  S
    s ="hi "; // assignment(=) operator
    s+="there"; //Concatenation assignment (+=) operator
    cout << s; // insertion (>>) operator
    return 0;
}

Output

hi there

Using  sub scripting [] operator  on a string

#include <iostream>
#include <string>
using namespace std;
int main ()
{
  string s ("hi there");
  for (int i=0; i<s.length(); i++)
  {
    cout << s[i]; // [] sub scripting operator
  }
  return 0;
}

Output

hi there

Using  inequality(!=)  operator  on a string

#include <iostream>
#include <string>
using namespace std;
int main()
{
string s1("hi_there"); // string object s1
string s2("hi_there"); // string object s2
if(s1 != s2) //  inequality operator(!=)
cout<<"s1 and s2 are not equal."<<endl;
else
cout<<"s1 and s2 are equal."<<endl;
  return 0;
}

Output

s1 and s2 are equal

Using  equality(==)  operator  on a string

#include <iostream>
#include <string>
using namespace std;
int main()
{
string s1("hi_there");
string s2("hi_there_people");
if(s1 == s2)
cout<<"s1 and s2 are equal."<<endl;
else
cout<<"s1 and s2 are not equal."<<endl;
  return 0;
}

Output

s1 and s2 are not equal

Using  Greater than (>)  operator  on a string

#include <iostream>
#include <string>
using namespace std;
int main()
{
string s1("hi_there");
string s2("hi_there_people");
if(s1 > s2)
cout<<"s1 is greater than s2 "<<endl;
else
cout<<"s1 is less than s2 "<<endl;
  return 0;
}

Output

s1 is less than s2

Using less than (<)  operator  on a string

#include <iostream>
#include <string>
using namespace std;
int main()
{
string s1("hi_there");
string s2("hi_there_people");
if(s1 < s2)
cout<<"s1 is greater than s2 "<<endl;
else
cout<<"s1 is less than s2 "<<endl;
  return 0;
}

Output

s1 is greater than s2

String  member functions

Assign() function

#include <iostream>
#include <string>
using namespace std;
int main()
{
    string s; //String with object  s
    s.assign("hi_there");//You can also directly assign  by s1 = ?hi_there?;
    cout<<s;
    return 0;
}

Output

hi_there

append() function

#include <iostream>
#include <string>
using namespace std;
int main()
{
    string s= "hi_there";
    s.append("people"); //You can also use s+= ?people?;
    cout<<s;
    return 0;
}

Output

hi_there people

insert( )function

Syntax

string object.insert(pos, value)

#include <iostream>
#include <string>
using namespace std;
int main()
{
    string obj= "hi_people";
    obj.insert(2,"_there"); 
    cout<<obj;
    return 0;
}

Output

hi_there_people

replace() function

syntax

string object .replace(pos, length,value)

#include <iostream>
#include <string>
using namespace std;
int main()
{
    string obj= "hi_people";
    obj.replace(2,7,"_there"); 
    cout<<obj;
    return 0;
}

Output

hi_there

erase() function

#include <iostream>
#include <string>
using namespace std;
int main()
{
    string obj= "hi_people";
    obj.erase();
    cout<<obj;
    return 0;
}

Output

find() function

#include <iostream>
#include <string>
using namespace std;
int main()
{
    string obj= "hi_there_people";
    int i =obj.find("there");
    cout<<i;
    return 0;
}

returns

index value of given text

Output

3

size() function

#include <iostream>
#include <string>
using namespace std;
int main()
{
    string obj= "hi_there_people";
    int i =obj.size();
    cout<<i;
    return 0;
}

Output

15

at() function

#include <iostream>
#include <string>
using namespace std;
int main()
{
    string obj= "hi_there_people";
    cout<<obj.at(4);
    return 0;
}

Output

h

data() function

#include <iostream>
#include <string>
using namespace std;
int main() {
   string s1 = "hi_there";

   cout<<s1.data();

   return 0;
}

Output

hi_there

find_first_of() function

#include<iostream>
using namespace std;
int main()
{
string obj = "hi_there_people";
cout  << obj.find_first_of('t');
return 0;
}

return

gives the position of the first occurrence of a given letter from the string

Output

3

find_last_of() function

#include<iostream>
using namespace std;
int main()
{
string obj = "hi_there_people";
cout  << obj.find_last_of('h');
return 0;
}

return

gives the position of the last occurrence of a given letter from the string

Output

14

c_str() function

c_str() function convert c++style string into c style string

c_str returns a const char* (which is a C style string)

#include <iostream>
#include <string.h>
using namespace std;
int main() {
    string s1="hello";
    cout<<s1.c_str();
}

Output

hello

convert c++style string into c style string without c_str() function

#include <iostream>
#include <string.h>
using namespace std;
int main() {
    string s1="hello"; // c++ string
    char str[30];      // c string
    strcpy(str,s1); //convert c++ string(s1) to C string(str)
    cout<<str;
}

Output

Error : cannot convert std::string to basic_string<char>

convert c++style string into c style string with c_str() function

#include <iostream>
#include <string.h>
using namespace std;
int main() {
    string s1="hello"; // c++ string
    char str[30];      // c string
    strcpy(str,s1.c_str()); //convert c++ string(s1) to C string(str)
    cout<<str;
}

Output

hello

List class

Syntax

Here one, two, and three are the list objects

#include <iostream>
#include <list>
using namespace std;
int main()
{
    list<int> v={1,2,3,4,5,6,7};
    v.push_back(8);
    v.push_back(9);
    for(int x:v)
        cout<<x<<endl;
    return 0;
}

Output

1 2 3 4 5 6 7 8 9

NOTE:  you can use other container class by including header file and declaring its class

every container class have a different member functions

 for an instant, forward_list class won’t have push_back member function, it has push_front  member function

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