All about pair STL in c++ for competitive programming( initialization, traversal and methods/functions ) :

pair STL

Important Points:

1. It is a simple utility container which consists of a single pair.
   
2. A pair contains values (t1 and t2) which may be of different types.
   
3. It provides a way to store two heterogeneous objects as a single unit.
4. Keyword 'first' is used to refer to the first value (t1) and keyword 'second' is used to refer to the second value (t2) .
5. A pair can be copied and can be compared with other pairs also.
6. Remember to use the header file #include<utility> before using pair STL.
   

  map and pair:

• map STL uses pair only to store (key, value) pairs in it. 
• By default, first value (t1) is the key and the second value (t2) is the value associated with the key.
  

 

 

 

Different ways to initialize a pair STL

 

1. declaring a pair and using make_pair( ) to make a pair :  

    pair < int, string > p ;
    p = make_pair ( 10, "gamma" ) ;
    

 

2. using first and second keyword to make a pair:  

    pair < int, string > p ;
    p.first = 10 ;

    p.second = "gamma" ;

 

 

3. initializing during declaration only:  

    pair < int, string > p ( 10, "gamma" ) ;

 

 

4. Initializing from another pair:

    

    pair < int, string > p2 ( 10, "gamma" ) ;

 

    pair < int, string > p ( p2 ) ;

 

                      or

 

     p = p2 ; 
  

 

 

 

 

**don't worry about the methods / functions used above, i am going to explain each and every function associated with pair STL below.

 

 

 

All pair STL methods/ functions  

pair STL important functions:

1. make_pair( ) : used to make a pair.

 

2. swap( ) : used to exchange the content of two pairs of  same type.

 

3. operator " = " : used to copy the content of a pair into a new pair.

 

4. relational operators " = =, ! =, <, >, > =, < = " : used to compare two pairs. (Note: Comparing is done on the basis of key or first value i.e t1)

 

  
Other functions:

•  tie( )
•  get( )

 

 

 

 

 

List of all pair STL important functions with example 

 

1. Initializing pairs : pair < int, string > p1, p2 ;

 

2. Putting elements into them : 

     p1 = make_pair ( 10, "alpha" ) ;

     p2 = make_pair ( 90, "beta" ) ;

 

3. using relational operators to compare them :

    if( p1 = = p2 )

    cout << "p1 = p2" ;  

  

    if( p1 ! = p2 )

    cout << "p1 ! = p2" ;     //it will be printed 

 

    if( p1 < p2 )

    cout << "p1 < p2" ;     //it will be printed

 

    if( p1 > p2 )

    cout << "p1 > p2" ;

  

    if( p1 < = p2 )

    cout << "p1 < = p2" ;     //it will be printed 

 

    if( p1 > = p2 )

    cout << "p1 > = p2" ;        

 

4. using" = " operator :

    //declaring another pair p3

    pair < int, string > p3 ;

    p3 = p1 ;

    Therefore, 

    p3 = (10, "alpha")

 

5. swap(p1, p2)      // pair p1 and p2 swapped

pair STL traversal method 

 

Let our pair be p :

pair < int, string > p ;

 

cout << p.first << " " << p.second ;

 

 

 

 

 

 

 

 

Hi reader! got any queries or need more explanation for something? Feel free to comment below.