問題描述

我有一個(gè)運(yùn)行 15 次的 for 循環(huán)，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 所做的是調(diào)用 srand(time(0))，然后每當(dāng)需要隨機(jī)數(shù)時(shí)它都會(huì)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.

現(xiàn)在，通常decider和carSetter以不同的方式使用，但我懷疑有問題并打印出carSetter和decider 在每次迭代中.這是結(jié)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...

當(dāng)我多次運(yùn)行它時(shí)，值1"和2"會(huì)發(fā)生變化，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.

既然循環(huán)運(yùn)行了 15 次不同的時(shí)間，難道 carSetter 和 decider 不應(yīng)該每次迭代都打印出不同的隨機(jī)數(shù)嗎?

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

當(dāng)我沒有 srand(time(0)) 時(shí)，它按預(yù)期工作，但是沒有種子集，所以每次都是相同的隨機(jī)"數(shù)字序列，所以它是可能是種子有問題?

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?

推薦答案

當(dāng)你調(diào)用 srand(x) 時(shí)，那么 x 的值決定了偽序列在對(duì) rand() 的后續(xù)調(diào)用中返回的隨機(jī)數(shù)，完全取決于 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.

當(dāng)您處于循環(huán)中并在頂部調(diào)用 srand() 時(shí):

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

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

然后根據(jù)time(0)返回的值生成相同隨機(jī)數(shù)序列.由于計(jì)算機(jī)速度很快，而且您的循環(huán)可能會(huì)在不到一秒的時(shí)間內(nèi)運(yùn)行，time(0) 每次通過循環(huán)都會(huì)返回 相同 值.所以 x 和 y 每次迭代都是一樣的.

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開始時(shí)調(diào)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，x 和 y 每次循環(huán)都會(huì)有不同的值.

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

這篇關(guān)于每次循環(huán)迭代相同的隨機(jī)數(shù)的文章就介紹到這了，希望我們推薦的答案對(duì)大家有所幫助，也希望大家多多支持html5模板網(wǎng)！