Just Two Characters Different

Here is a fragment of the program, with those two braces removed:

    if ( N >= 0 )
    {
      while ( N > 1 )    
 
        fact = fact * N;
        N    = N - 1;
      
      System.out.println( "factorial is " + fact );
    }
    else
    {
      System.out.println("N must be zero or greater");
    }

This fragment looks OK, but remember that blank lines and indenting are for people, not for the compiler. What the compiler sees is:

    if ( N >= 0 )
    {
      while ( N > 1 )     
        fact = fact * N;

      N    = N - 1;      
      System.out.println( "factorial is " + fact );
    }
    else
    {
      System.out.println("N must be zero or greater");
    }

Now, it is clear that N does not change. The condition N > 1 is always true, and the loop continues forever.