CODEWITHSUNDEEP
javacmathrandom
John R
John R

Reputation: 389

Random number generation in C vs Java

I was curious to know why random_number=a+rand()%b; in C produces a random number between a and b (non-inclusive of b). But in Java this code will not work. I understand that the correct way to do this in Java is random_number=a+(Math.random()*(b-a)); but I was curious to know why there is a difference? Isn't it the same operation mathematically? I also understand that the return types are different for the random functions, but how does this difference explain the difference in output? Sorry if this seems like a trivial question but I was curious nonetheless.

Upvotes: 0

Views: 3080

Answers (3)

Sohil Omer
Sohil Omer

Reputation: 1181

In java it is nextInt()

int nextInt(int n)

This function returns random number between 0 to n

In C it is rand()

int rand(void)

This function returns an integer value between 0 and RAND_MAX.

Upvotes: 0

Hot Licks
Hot Licks

Reputation: 47729

One can, of course use java.util.Random's nextInt() or nextInt(int n) method to more exactly mimic the C scheme. nextInt() is almost exactly the same as rand() (though hopefully better distributed) while nextInt(int n) effectively subsumes the %n calculation.

Upvotes: 2

rgettman
rgettman

Reputation: 178263

The difference lies in what each random generator does.

In Java, Math.Random returns a pseudo-random number of the range 0 (inclusive) through 1 (exclusive). So it must be scaled up by b - a, the width of the range, then shifted by a, the start of the range.

In C, rand() returns numbers in the range 0 to RAND_MAX (my RAND_MAX is 32767), so %b is used to control the width of the range, and the start of the range is shifted by a.

Upvotes: 6

Related Questions