blocks|key|664230|text|您需要在程序开始时运行srand，例如在main-function中。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|664231|当您在使用rand()的函数的顶部运行srand(time(0))时，您很可能每次都会给它提供相同的种子。time(0)以秒为单位提供时间，因此您需要避免在同一秒内调用setDoors两次，以便每次都获得不同的数字。如果您在同一秒内调用setDoors两次，则随机种子将是相同的，并且后续对rand()的调用将生成相同的伪随机数序列。|664232|entityMap^0|B|5|K|4|0|5|6|J|E|1H|7|2C|8|3A|8|41|6|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]|$9|T|A|U|B|C]|$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|11|8|@]|D|@]|E|$]]]|I|$]]

You need to run <code>srand</code> in the beginning of your program, for example in the <code>main</code>-function.

When you run <code>srand(time(0))</code> at the top of the function in which you are using <code>rand()</code>, you are likely to give it the same seed every time. <code>time(0)</code> gives the time in seconds, so you would need to avoid calling <code>setDoors</code> twice within the same second in order to get different numbers every time. If you do call <code>setDoors</code> twice within the same second, the random seed will be the same, and subsequent calls to <code>rand()</code> will generate the same sequence of pseudorandom numbers.

blocks|key|4701376|text|正如Kerrek所说，播种只在程序开始时进行一次。在一次srand之后，你可以任意多次调用rand。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4701377|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Like Kerrek said, seeding is done only once, in the beginning of the program. After one srand call rand as many times as you like.

blocks|key|1580167|text|当您调用srand(x)时，x的值决定了在随后的rand()调用中返回的伪随机数序列，这完全取决于x的值。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1580168|当您在循环中并在顶部调用srand()时：|1580169|while+(...)+{
++++srand(time(0));
++++x+=+rand();
++++y+=+rand();
}|code-block|syntax|javascript|1580170|然后，根据time(0)返回的值生成相同的随机数序列。由于计算机运行速度很快，而您的循环运行时间可能不到一秒，因此time(0)每次循环都会返回相同的值。因此，x和y在每次迭代中都是相同的。|1580171|相反，您通常只需要在程序开始时调用srand()一次：|1580172|srand(time(0));

while+(...)+{
++++x+=+rand();
++++y+=+rand();
}|1580173|在上面的例子中，x和y在每次循环中都会有不同的值。|1580174|entityMap^0|4|8|E|1|O|6|1D|1|0|C|7|0|0|5|7|1L|7|28|1|2A|1|0|H|7|0|0|8|1|A|1|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|15|8|@$9|16|A|17|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|18|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|19|8|@$9|1A|A|1B|B|C]|$9|1C|A|1D|B|C]|$9|1E|A|1F|B|C]|$9|1G|A|1H|B|C]]|D|@]|E|$]]|$1|O|3|P|5|6|7|1I|8|@$9|1J|A|1K|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|J|7|1L|8|@]|D|@]|E|$K|L]]|$1|S|3|T|5|6|7|1M|8|@$9|1N|A|1O|B|C]|$9|1P|A|1Q|B|C]]|D|@]|E|$]]|$1|U|3|-4|5|6|7|1R|8|@]|D|@]|E|$]]]|V|$]]

When you call <code>srand(x)</code>, then the value of <code>x</code> determines the sequence of pseudo-random numbers returned in following calls to <code>rand()</code>, depending entirely on the value of <code>x</code>.

When you're in a loop and call <code>srand()</code> at the top:

<pre><code>while (...) {
 srand(time(0));
 x = rand();
 y = rand();
}
</code></pre>

then the same random number sequence is generated depending on the value that <code>time(0)</code> returns. Since computers are fast and your loop probably runs in less than a second, <code>time(0)</code> returns the same value each time through the loop. So <code>x</code> and <code>y</code> will be the same each iteration.

Instead, you only usually need to call <code>srand()</code> once at the start of your program:

<pre><code>srand(time(0));

while (...) {
 x = rand();
 y = rand();
}
</code></pre>

In the above case, <code>x</code> and <code>y</code> will have different values each time through the loop.

blocks|key|4701464|text|每次调用srand(time(0))时，您都在播种伪随机数生成器，向其注入一个新的伪随机数序列。序列是不同的，这取决于srand的参数是什么，在本例中，您使用time(0)，因此，假设您每秒最多调用程序一次，您将始终获得一个新序列。当您调用rand()时，您只需获取此序列中的下一个数字。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4701465|但是，由于您已经决定在程序中多次调用srand，而且您的程序速度很快(即time(0)没有变化)，所以您所要做的就是重复地将PRNG重置为相同的顺序。这就是为什么你总是得到相同的值-你不断地将PRNG重新设定为相同的序列，这也会将光标移动到序列的开头。|4701466|种子一次。一次。|BOLD|4701467|entityMap^0|4|E|1N|5|27|7|3C|6|0|I|5|10|7|0|0|8|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]|$9|R|A|S|B|C]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|V|8|@$9|W|A|X|B|C]|$9|Y|A|Z|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|10|8|@$9|11|A|12|B|J]]|D|@]|E|$]]|$1|K|3|-4|5|6|7|13|8|@]|D|@]|E|$]]]|L|$]]

Every time you invoke <code>srand(time(0))</code>, you're seeding the pseudo-random number generator, imbuing it with a new pseudo-random sequence of numbers. The sequence is different depending on what the argument to <code>srand</code> is, and in this instance you use <code>time(0)</code> so, assuming you call your program at most once per second, you'll always get a new sequence. When you call <code>rand()</code>, you just get the next number in this sequence.

However, since you've decided to call <code>srand</code> multiple times in your program, and because your program is fast (i.e. <code>time(0)</code> isn't changing), all you're doing is repeatedly resetting the PRNG to the same sequence. That's why you're always getting the same values - you keep reseeding the PRNG to be the same sequence, and this also moves the cursor to the beginning of the sequence.

Seed once. Once.

I have a <code>for</code> loop that runs 15 times, with <code>dh.setDoors()</code> in every iteration.

What <code>setDoors</code> does is call <code>srand(time(0))</code>, then whenever a random number is needed it'll use, for example, <code>carSetter = rand()%3+1</code>. Alternatively, it may use <code>decider = rand()%2+1</code>.

Now, normally <code>decider</code> and <code>carSetter</code> are used in a different ways, but I suspected a problem and made it print out <code>carSetter</code> and <code>decider</code> at every iteration. Here's what came out:

<pre><code>Door 1 has car
Decider is 2
Door 1 has car
Decider is 2
Door 1 has car
Decider is 2
Door 1 has car
Decider is 2
Door 1 has car
Decider is 2
etc...
</code></pre>

The values '1' and '2' change when I run it multiple times, but are still the same throughout the 15 times.

Since the loop is running 15 different times, shouldn't <code>carSetter</code> and <code>decider</code> print out a different random number every iteration?

When I don't have <code>srand(time(0))</code>, it works as expected, but there's no seed set, so it's the same sequence of "random" numbers each time, so it's probably a problem with the seed?

Same random numbers every loop iteration

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我有一个运行15次的for循环，每次迭代都有dh.setDoors()。setDoors所做的是调用srand(time(0))，然后每当需要一个随机数时，它都会使用，例如，carSetter = rand()%3+1。或者，它可以使用decider = rand()%2+1。现在，通常decider和carSette...

问每次循环迭代都有相同的随机数
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问每次循环迭代都有相同的随机数EN