为什么我总是用 rand() 得到相同的随机数序列? [英] Why do I always get the same sequence of random numbers with rand()?

问题描述

这是我第一次用 C 尝试随机数(我想念 C#).这是我的代码:

This is the first time I'm trying random numbers with C (I miss C#). Here is my code:

int i, j = 0;
for(i = 0; i <= 10; i++) {
    j = rand();
    printf("j = %d
", j);
}

使用此代码，每次运行代码时我都会得到相同的序列.但是如果我在 for 循环之前添加 srand(/*somevalue/*) ，它会生成不同的随机序列.谁能解释一下为什么?

with this code, I get the same sequence every time I run the code. But it generates different random sequences if I add srand(/*somevalue/*) before the for loop. Can anyone explain why?

推荐答案

你必须播种它.随时间播种是个好主意:

You have to seed it. Seeding it with the time is a good idea:

srand()

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main ()
{
  srand ( time(NULL) );
  printf ("Random Number: %d
", rand() %100);
  return 0;
}

您会得到相同的序列，因为如果您不调用 srand()，rand() 会自动以 a 值作为种子.

You get the same sequence because rand() is automatically seeded with the a value of 1 if you do not call srand().

由于评论

rand() 将返回一个介于 0 和 RAND_MAX(在标准库中定义)之间的数字.使用 modulo 运算符 (%) 给出除法的余数 <代码>rand()/100.这将强制随机数在 0-99 范围内.例如，要获得 0-999 范围内的随机数，我们将应用 rand() % 1000.

rand() will return a number between 0 and RAND_MAX (defined in the standard library). Using the modulo operator (%) gives the remainder of the division rand() / 100. This will force the random number to be within the range 0-99. For example, to get a random number in the range of 0-999 we would apply rand() % 1000.

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