0   1   2   3   4   5   6   7   8   9  10  11  12  13  14  15
    -----------------------------------------------------------------
 s: | S | U | M | M | E | R | T | I | M | E |   | B | L | U | E | S |
    -----------------------------------------------------------------

 c: '\n'    q: 5-->4      t: 7-->2-->1

 len: 16

 OUTPUT:   RPI\n
           RULES

3.

   int sum_evens_m_to_n( int m, int n )
   {
      if ( m < 0  ||  n < 0 ) {    // INVALID m OR n
        return -1;
      }

      int sum = 0;

      if ( m > n ) {    // swap m and n
        int temp = m;
        m = n;
        n = temp;
      }

      for ( int i = m ; i <= n ; i++ ) {
        if ( i % 2 == 0 ) {
          sum += i;
        }
      }
      return sum;
   }

   int sum_evens_2_to_n( int n ) {
     return sum_evens_m_to_n( 2, n );
   }




            0    1    2    3    4    5    6    7
4.        ----------------------------------------
 numbers: |  0 |-10 |-20 |-30 |-40 |-50 | 60 | ...
          ----------------------------------------


   OUTPUT:
   --------
   40.00
   20.00
   -3200.00
   -2.00
   --------