cppreference.com > C++ Algorithms > fill fill Syntax:
      #include <algorithm>
      #include <algorithm>
      void fill( iterator start, iterator end, const TYPE& val );
The function fill() assigns val to all of the elements between start and end. For example, the following code uses fill() to set all of the elements of a vector of integers to -1:
     vector<int> v1;
     for( int i = 0; i < 10; i++ ) {
       v1.push_back( i );
     }

     cout << "Before, v1 is: ";
     for( unsigned int i = 0; i < v1.size(); i++ ) {
       cout << v1[i] << " ";
     }
     cout << endl;

     fill( v1.begin(), v1.end(), -1 );

     cout << "After, v1 is: ";
     for( unsigned int i = 0; i < v1.size(); i++ ) {
       cout << v1[i] << " ";
     }
     cout << endl;
When run, the above code displays:
     Before, v1 is: 0 1 2 3 4 5 6 7 8 9
     After, v1 is: -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
Related topics: fill_n generate iota transform