每次循环迭代相同的随机数

Same random numbers every loop iteration(每次循环迭代相同的随机数)

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问题描述

我有一个运行 15 次的 for 循环,每次迭代都使用 dh.setDoors().

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

setDoors 所做的是调用 srand(time(0)),然后每当需要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.

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

现在,通常decidercarSetter以不同的方式使用,但我怀疑有问题并打印出carSetterdecider 在每次迭代中.这是结果:

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

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...

当我多次运行它时,值1"和2"会发生变化,但在 15 次中仍然相同.

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

既然循环运行了 15 次不同的时间,难道 carSetterdecider 不应该每次迭代都打印出不同的随机数吗?

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

当我没有 srand(time(0)) 时,它按预期工作,但是没有种子集,所以每次都是相同的随机"数字序列,所以它是可能是种子有问题?

When I don't have srand(time(0)), 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?

推荐答案

当你调用 srand(x) 时,那么 x 的值决定了伪序列在对 rand() 的后续调用中返回的随机数,完全取决于 x 的值.

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

当您处于循环中并在顶部调用 srand() 时:

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

while (...) {
    srand(time(0));
    x = rand();
    y = rand();
}

然后根据time(0)返回的值生成相同随机数序列.由于计算机速度很快,而且您的循环可能会在不到一秒的时间内运行,time(0) 每次通过循环都会返回 相同 值.所以 xy 每次迭代都是一样的.

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

相反,您通常只需要在程序开始时调用 srand() 一次:

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

srand(time(0));

while (...) {
    x = rand();
    y = rand();
}

在上面的例子中,xy 每次循环都会有不同的值.

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

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