Use std::fill_n to fill the first five elements of chars with 'A' : fill_n « STL Algorithms Modifying sequence operations « C++ Tutorial

1. C++ Tutorial
2. STL Algorithms Modifying sequence operations
3. fill_n

#include <iostream>
using std::cout;
using std::endl;

#include <algorithm> // algorithm definitions
#include <vector>    // vector class-template definition
#include <iterator>  // ostream_iterator

int main()
{
   std::vector< char > chars( 10 );
   std::ostream_iterator< char > output( cout, " " );
   std::fill( chars.begin(), chars.end(), '5' ); // fill chars with 5s
  // fill first five elements of chars with As
   std::fill_n( chars.begin(), 5, 'A' );


   cout << "Vector chars after filling with 5s:\n";
   std::copy( chars.begin(), chars.end(), output );
   cout << endl;
   return 0;
}

Vector chars after filling with 5s:
A A A A A 5 5 5 5 5