Computer Science Canada random number |
| Author: | starlight [ Mon Oct 31, 2005 9:44 pm ] |
| Post subject: | random number |
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 |
|
| Author: | beard0 [ Mon Oct 31, 2005 10:10 pm ] |
| Post subject: | |
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 |
|
| Author: | Naveg [ Mon Oct 31, 2005 10:12 pm ] |
| Post subject: | Re: random number |
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. |
|
| Author: | [Gandalf] [ Mon Oct 31, 2005 10:16 pm ] |
| Post subject: | |
The general format for random numbers in any language is this: RandomInteger = (int) (Math.random() * maxNumber) + minNumber; *edit* Oops, right beard0. |
|
| Author: | beard0 [ Mon Oct 31, 2005 10:26 pm ] |
| Post subject: | |
[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 |
|
| Author: | starlight [ Sun Nov 06, 2005 5:03 pm ] | ||
| Post subject: | |||
Thanks. on the other notes. i am pretty confuse with when you can add the arithmetic and character together. for example why does
|
|||
| Author: | beard0 [ Mon Nov 07, 2005 2:39 pm ] | ||||
| Post subject: | |||||
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
It has to do with the way types are interpreted. To be safe, explicitly change types, or use the increment operator: e.g.
|
|||||