meaning of e or E in JAVA e or E means 10 to the power not the e(2.718...) in maths comma operator in JAVA only use in iterator for, e.g for(int i = 0, j = 1, k = 2;i < 5;i++,j++,k--){ //do something } p.s.i j k must be the same data type practice: Find vampire numbers from all 4 digit numbers java code link