Too many arguments to function 'rand'?

Question

I have only used the function twice and it displays the aforementioned error. Can someone explain as to why the compiler does that?

void printrandom()
{
    int x = (rand(5)+1);
    int y = (rand(5)+1);
    printf("%d and %d - a total of %d", x, y, (x+y));
}

you can also try creating a function that will help you get a range int rand_num(int from, int to) { if (from == to) return to; else { int randNumber = from + (random() % (to - from)); } } — rocksyne, Jul 14 '20 at 21:44

score 2 · Answer 1 · edited May 23 '17 at 11:51

2

It is actually rand(void), which is why you are getting that error.

Try int x = (rand() % 5) + 1;

EDIT as Daniel points out, using % will actually affect the probability. See his link for how to address this issue.

edited May 23 '17 at 11:51

Community

answered Feb 09 '14 at 18:54

schumacher574

-1. Using `rand() % N` is flawed and should be avoided. See [this question](http://stackoverflow.com/questions/10984974/why-do-people-say-there-is-modulo-bias-when-using-a-random-number-generator) to find out why. – Daniel Kamil Kozar Feb 09 '14 at 18:56
@DanielKamilKozar; Good link. Thanks :) – haccks Feb 09 '14 at 19:00
4

@DanielKamilKozar: If the bias introduced by `rand() % 5` is a significant problem, then you should probably be using something better than `rand` anyway. – Keith Thompson Feb 12 '14 at 21:15

haccks · Answer 2 · 2014-02-12T21:00:43.453

0

Declaration for rand() function is

int rand(void);

This means that it takes no arguments. Remove 5 from rand. If you want to generate random numbers from 1 to 5, the you can do this as

int x = rand()%5 + 1;

edited Feb 12 '14 at 21:00

answered Feb 09 '14 at 18:55

haccks

1

Indeed, that is another option. But it will perform on average 400 million iterations to generate an in-range number... – Oliver Charlesworth Feb 09 '14 at 19:29
@OliCharlesworth; True. But what is wrong with the answer. I mentioned both approaches. – haccks Feb 09 '14 at 19:34
Because what you've presented is a really bad solution ;) – Oliver Charlesworth Feb 09 '14 at 19:34
@OliCharlesworth; Then you can go with first one. It is up to you ;) – haccks Feb 09 '14 at 19:36
1

@OliCharlesworth: I agree (and he's edited his answer), but the expected number of iterations depends on the value of `RAND_MAX`, which can be as small as `32767`. – Keith Thompson Feb 12 '14 at 21:14
@KeithThompson: That is true. – Oliver Charlesworth Feb 12 '14 at 22:59

2 Answers2