Difficulties with a++, ++a

++a is a pre-incrementation. Which means that a is incremented before returning the value of a.

a++ is a post-incrementation. Which means that a is incremented after returning the value of a.

In other words, a++ gives the current value of a and then increment it. While ++a directly increment a. If a=42 then System.out.println(a++) gives 42 while System.out.println(++a) gives 43 and in both cases, a=43 now.

OP also asked for a line by line explanation of that code:

import java.util.Scanner; public class Number { public static void main(String[] args) { Scanner keyboard = new Scanner(System.in); int number = keyboard.nextInt(); int division1 = (number++) % 10; number = number / 10; System.out.println(number % 10+division1); } } 

I guess, only the code inside the main function need some explanations :

 // Create a Scanner object that read from the standard input. Scanner keyboard = new Scanner(System.in); // Read an integer. int number = keyboard.nextInt(); // put (number % 10) into variable division1 and then increment `number`. int division1 = (number++) % 10; // Divide number by 10. number = number / 10; // Print that expression : System.out.println(number % 10+division1); 

The line int division1 = (number++) % 10; might not be very clear. It would be simpler to read like that:

int division1 = number % 10; number += 1; 

Now, the explanation of what the function does:

If number = 142, we put 2 into variable division1, then number is incremented and divided by 10. So number gets the value 14 ((142+1) / 10). And now we print number % 10 + division1 which is 4 + 2 = 6.

Here some examples of results (I've compiled the code myself):

3 => 3 9 => 10 10 => 1 248 => 12 

Literally line-by-line explanation:

import java.util.Scanner; // Import Scanner public class Number { // Create Java class called Number public static void main(String[] args) { // Define the main function Scanner keyboard = new Scanner(System.in); // Initialize the scanner int number = keyboard.nextInt(); // Read an integer from standard input int division1 = (number++) % 10; // Take the unit digit of number, then increase number by 1 number = number / 10; // Divide number by 10 // Take the tens digit of the original number (or tens digit + 1, if the unit was 9), sum with the unit digit previously stored in division1 System.out.println(number % 10+division1); // The result would sum the last two digit of number if it doesn't end with 9, or sum the last two digit +1 if the unit was 9. } } 

Some cases:

 f(1) = 1 f(124) = 2+4 = 6 f(39) = 4+9 = 13 f(5248) = 4+8 = 12 

I think, the interesting part for you are the following lines:

int number = keyboard.nextInt(); 

Here, you get an input from the user. Say, he enters 12

int division1 = (number++) % 10; 

division1 will become 2, because 12 mod 10 equals 2. After this, number will be incremented by 1, so it is now 13

Let's now assume there would be a ++number instead of number++. In this case, we would increment number before the modulo operation. So, first, number becomes 13, then we assign 3 to division1.

And that's the basic thing about a++ and ++a - the time, when the value is incremented. a++ means, all operations use a as it is and as a last step, a is incremented. ++a works in the other order.

++a is a pre-incrementation. Which means that a is incremented before the expression is evaluated.

a++ is a post-incrementation. Which means that a is incremented after the expression is evaluated.

One thing where beginners might be confused is what is this 'expression' after which the increment takes place It is actually the ; When you use a++, it is after the ";" when the increment actually takes place and when you use ++a; it is just as you inserted a statement before this one saying a=a+1 and then your expression comes.