1. sort() function for Array

1.1. Sort in ascending order:

• sort(arr + desired starting index , arr + desired ending index ); [indexing start from 1]
• sort(arr (by default index: 1) , arr + desired ending index ); [indexing start from 1]

1.2. Sort in descending order:

• sort(arr + desired starting index , arr + desired ending index , greater<'int'>()); [indexing start from 1] ['int' without quotation]

2. sort() function for Vector

2.1. Sort in ascending order:

• sort(vec.begin() + desired starting index , vec.begin() + desired ending index ); [indexing start from 0]
• sort(vec.begin() (by default index: 0) , vec.end()); [end() for last index]

2.2. Sort in descending order:

• sort(vec.begin() + desired starting index , vec.begin() + desired ending index + 1, greater<'int'>()); [indexing start from 0] ['int' without quotation]
• sort(vec.begin() (by default index: 0) , vec.end(), greater<'int'>()); [end() for last index] ['int' without quotation]

2.3. sort() function for Vector Pair:

2.3.1. On the basis of first element:

• sort(vec.begin(), vec.end()); [Ascending order]
  

• sort(vec.begin(), vec.end(), greater<pair<int, int>>()); [Descending order]
  

  2.3.2. On the basis of second element:
  

  [Ascending order]
  bool sortbysec(const std::pair<int, int> &a, const std::pair<int, int> &b){return a.second < b.second;}
  sort(vec.begin(), vec.end(), sortbysec);
  
  [Descending order]
  bool sortbysecdesc(const std::pair<int, int> &a, const std::pair<int, int> &b){return a.second > b.second;}
  sort(vec.begin(), vec.end(), sortbysecdesc);

In the following sort function of C++ how the 3rd argument is working?

sort(a.begin(), a.end(), [](int x, int y) { return x % 2 < y % 2; });