random number

[starlight]

int dieroll;
dieroll=(int)(6*Math.random())+1

the above lines generate random numbers between 1-6 but i don't really get what the "+1" at the end of the statment is for. anyone can explain? Like if i want to generate a number between 1 and 6 (not including 6) why can't i just simply use "dieroll=(int)(7*Math.random())"

and the other quesiton is

char int d=7
int dd
dd=d++

doesn't d++ mean d=d+1 so shouldn't dd be 8 and d be 7. Why when i tested it means the other way around (d =8 while dd =7)?

and lastly one strange thing that i found in Java is why 3.0/(15/6) equals to 1.5 If 3.0/(15/6) is equal to 1.5 then 15/6 has to equal to 2 meaning the answer will round down. why is that.

Thanks

[beard0]

When you convert (6*Math.random())+1 to an integer, you aren't rounding it, you are truncating it, meaning only if Math.Random returned exactly 1.0 (I'm not sure even if it can) would you end up with a final result of 7. Your second option would have 0 as a possible result.

dd=d++:

d++ returns the value d, and increments d

[Naveg]

starlight wrote:

int dieroll;
dieroll=(int)(6*Math.random())+1

the above lines generate random numbers between 1-6 but i don't really get what the "+1" at the end of the statment is for. anyone can explain? Like if i want to generate a number between 1 and 6 (not including 6) why can't i just simply use "dieroll=(int)(7*Math.random())"

and the other quesiton is

char int d=7
int dd
dd=d++

doesn't d++ mean d=d+1 so shouldn't dd be 8 and d be 7. Why when i tested it means the other way around (d =8 while dd =7)?

and lastly one strange thing that i found in Java is why 3.0/(15/6) equals to 1.5 If 3.0/(15/6) is equal to 1.5 then 15/6 has to equal to 2 meaning the answer will round down. why is that.

Thanks

1) Math.random() generates a number between 0 and 1. Since the first value you are choosing from is 1, you add 1 (0+1=1)

2)This comes down to prefix and postfix operators. The prefix (++d) will increment the variable and then use the new value in the expression. However, the postfix (d++) first uses the variable and only then increments its value.

3) 15/6 is integer division. In such a case, any decimal is truncated (cut off). Be careful not to confuse this with rounding, 3.778 will become 3! So in this example, 15/6 is 2.5, but because of integer division the decimal is truncated and it becomes 2.

[[Gandalf]]

The general format for random numbers in any language is this:

RandomInteger = (int) (Math.random() * maxNumber) + minNumber;

*edit* Oops, right beard0.

[beard0]

[Gandalf] wrote:

The general format for random numbers in any language is this:

RandomInteger = (int) (Math.random() * maxNumber) + minNumber;

errr.....

RandomInteger = (int) (Math.random() * (maxNumber-minNumber+1) + minNumber

[starlight]

Thanks. on the other notes. i am pretty confuse with when you can add the arithmetic and character together. for example
why does

code:

char c='A'+1 or char c='A';c='A'+1 or char c='A'; c++; works; while something like char c='A'; c=c+1; doesn't

[beard0]

starlight wrote:

Thanks. on the other notes. i am pretty confuse with when you can add the arithmetic and character together. for example
why does

code:

char c='A'+1 or char c='A';c='A'+1 or char c='A'; c++; works; while something like char c='A'; c=c+1; doesn't

It has to do with the way types are interpreted. To be safe, explicitly change types, or use the increment operator:
e.g.

code:

char c = 'A'; c = ((char) (((int) c) + 3)); //for increasing by more than 1 or c++; //for increasing by 1