Copy all those element that need to be sorted to an auxiliary array b [ ]
int b [ n - ( u - l + 1 ) ] ; for ( int i = 0 ; i < l ; i ++ ) b [ i ] = a [ i ] ; for ( int i = u + 1 ; i < n ; i ++ ) b [ l + ( i - ( u + 1 ) ) ] = a [ i ] ;