Beginner question here: I tried creating a random number using this code
int rand = (int) Math.random()*10;
however, i kept receiving 0 as the answer when printing to screen
only after putting parenthesis like so
int rand = (int)(Math.random()*10);
did the number show properly. Can anyone explain the logical reason for this that I missed?
When you write int rand = (int) Math.random()*10, you're actually writing:
int rand = ((int) Math.random()) * 10;
Therefore you get 0 because the random number is between 0 and 1, and casting it to an int makes it equals to 0.
The code
int rand = (int) Math.random()*10;
is equivalent to
int rand = ((int) Math.random()) * 10;
So the value of Math.random() is converted to an int. Because that value is between 0 and 1 (1 excluded) it is converted always to zero.
So
(int) Math.random()*10 --> ((int) Math.random()) * 10 --> 0 * 10 --> 0
Math.random() returns a double number between 0 and 1 exclusive, which means (int)Math.random() will always be 0 (since Math.random() < 1). In order to perform the multiplication before the cast to int, you must use parentheses as you did.
The other answers already explained the issue with your code, so I won't cover this topic here anymore.
This is just a note on the generation of random-numbers:
The recommended way of generating random-numbers in java isn't Math.random() , but via the java.util.Random class (http://docs.oracle.com/javase/7/docs/api/java/util/Random.html).
To generate a random-number like in the above example, you can use this code:
Random rnd = new Random();
int i = rnd.nextInt(10);
, which will produce the same result as your code.
int rand = (int) Math.random()*10;
is equivalent to
int rand = ((int) Math.random())*10;
Considering that Math.random() return a number from 0<=N<1, if you try to cast it you will always get 0, that multiply by 10 is still 0
int rand = ((int) Math.random()); -- ALWAYS --> ZERO
0*N ---- ALWAYS ---> ZERO
