README.md

Pairs in C++ STL

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Pair in C++ is used to combine 2 values in it , and their datatypes may be same or not. Pairs are generally used in problems which need touples to carry into any datastructure.

The 1st value is pointed by first and next value is pointed by second. --- # Syntax:

1. Initialize a Pair:

pair<datatype1,datatype1>pair_name;
//example: pair<int,string>p1;
/* first value is type 'int'
and 2nd of type string*/ 

2. Insert values into pair

//1st way to insert valueds into pair
    p1=make_pair(1,"Amit");
//2nd way to insert valueds into pair
    p1={2,"santanu"};

3. Display content of Pair:

cout<<"Displaying elements of p1->"<<endl;
cout<<p1.first<<"-> "<<p1.second<<endl;
//Output: 2-> santanu
/*p1.first point to 1st value of pair p1 and p1.second points to 2nd value of pair p1.

4. Copying content from one pair to another:

  pair<int,int>p2= [10,20] ;
//define another pair
    
    pair<int,int>p3=p2; 
//here from p2 data is copied to new pair p3
//Display content of new copied pair
     cout<<"Displaying elements of p3->"<<endl;
    cout<<p3.first<<"->"<<p3.second<<endl;
/*OUTPUT:
Displaying elements of p3-> 10->20 */ 

5. Pair of Array.

 pair<char,int>p_arr[3];
    //hair a pair of array taken of size 3
    //taking values of p_arr[3]
    p_arr[0]={'A',1};
    p_arr[1]={'B',2};
    p_arr[2]={'C',3};
    //Printing all elements of pair of array
    cout<<"Printing all elements of pair of p_arr"<<endl;
    for(int i=0;i<3;i++){
        cout<<"No "<<i+1<<". element are--> "<<p_arr[i].first<<"->"<<p_arr[i].second<<endl;
}
/* OUTPUT:
Printing all elements of pair of p_arr
No 1. element are--> A->1
No 2. element are--> B->2
No 3. element are--> C->3
*/

6. Swapping between pairs.

//Swapping between two pairs
    pair<char, int> pair1 = make_pair('X', 100);
    pair<char, int> pair2 = make_pair('Y', 200);
    cout << "Before swapping the pairs "<<endl;
    cout << "elements of pair1 = " << pair1.first << "->"
         << pair1.second<<endl;
    cout << "elements of pair2 = " << pair2.first << "->"
         << pair2.second<<endl;
//swap between pair1 and pair2
    pair1.swap(pair2);
 //After swapping
    cout << "After swapping betwen pairs "<<endl;
    cout << "elements of pair1 = " << pair1.first << "->"
         << pair1.second<<endl;
    cout << "elements of pair2 = " << pair2.first << "->"
         << pair2.second<<endl;
/* OUTPUT:
Before swapping the pairs
elements of pair1 = X->100
elements of pair2 = Y->200
After swapping betwen pairs
elements of pair1 = Y->200
elements of pair2 = X->100
*/

7. Iterators in Pair

 vector<pair<int,int>>VP=[[1,2],[3,4],[5,6]];
 //initialize a vector containing pair in it.
 //iterator to access elements of the vector of pairs
 vector<pair<int,int>>::iterator it;
 //iterating over all elements
 for(it=vp.begin(); it!=vp.end();it++){
     cout<<(*it).first<<" "<<(*it).second<<endl;
 }
 /*OUTPUT
1->2
3->4
5->6