18) When N is integer, NOT N is equal to -1-N 19) A=A+1(A=A-1) is a little bit faster than INC A(DEC A). 20) Normally the result of comparison operation (e.g. A>B) is boolean (1:TRUE/0:FALSE). However, if we compare string variable and numerical variable like A$<B, the result will be 3. We can discriminate variable type with this phenomenon.