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    3. 为什么 rand() 每次运行都会产生相同的数字序列?

      时间:2023-06-05

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                本文介绍了为什么 rand() 每次运行都会产生相同的数字序列?的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着跟版网的小编来一起学习吧!

                问题描述

                每次我用 rand() 运行程序时,它都会给我相同的结果.

                示例:

                #include #include 使用命名空间标准;int随机(int低,int高){如果(低>高)回报高;返回低 + (rand() % (高 - 低 + 1));}int main (int argc, char* argv []) {for (int i = 0; i <5; i++)cout<<随机 (2, 5) <<结束;}

                输出:

                35423

                每次我运行程序时,它每次都会输出相同的数字.有没有办法解决这个问题?

                解决方案

                未设置随机数生成器的种子.

                如果你调用 srand((unsigned int)time(NULL)) 那么你会得到更多的随机结果:

                #include #include #include <ctime>使用命名空间标准;int main() {srand((unsigned int)time(NULL));cout<<兰特()<<结束;返回0;}

                原因是从 rand() 函数生成的随机数实际上并不是随机的.这简直就是一种转变.维基百科对伪随机数生成器的含义给出了更好的解释:确定性随机位生成器.每次调用 rand() 时,它都会获取生成的种子和/或最后一个随机数(C 标准没有指定使用的算法,尽管 C++11 具有指定一些流行的算法),对这些数字运行数学运算,并返回结果.因此,如果种子状态每次都相同(就像您不使用真正的随机数调用 srand 一样),那么您将始终得到相同的随机"数.

                如果您想了解更多,可以阅读以下内容:

                http://www.dreamincode.net/forums/topic/24225-random-number-generation-102/

                http://www.dreamincode.net/forums/topic/29294-making-pseudo-random-number-generators-more-random/

                Every time I run a program with rand() it gives me the same results.

                Example:

                #include <iostream>
                #include <cstdlib>
                
                using namespace std;
                
                int random (int low, int high) {
                    if (low > high)
                        return high;
                    return low + (rand() % (high - low + 1));
                }
                
                int main (int argc, char* argv []) {
                    for (int i = 0; i < 5; i++)
                        cout << random (2, 5) << endl;
                }
                

                Output:

                3
                5
                4
                2
                3
                

                Each time I run the program it outputs the same numbers every time. Is there a way around this?

                解决方案

                The seed for the random number generator is not set.

                If you call srand((unsigned int)time(NULL)) then you will get more random results:

                #include <iostream>
                #include <cstdlib>
                #include <ctime>
                using namespace std;
                
                int main() {
                    srand((unsigned int)time(NULL));
                    cout << rand() << endl;
                    return 0;
                }
                

                The reason is that a random number generated from the rand() function isn't actually random. It simply is a transformation. Wikipedia gives a better explanation of the meaning of pseudorandom number generator: deterministic random bit generator. Every time you call rand() it takes the seed and/or the last random number(s) generated (the C standard doesn't specify the algorithm used, though C++11 has facilities for specifying some popular algorithms), runs a mathematical operation on those numbers, and returns the result. So if the seed state is the same each time (as it is if you don't call srand with a truly random number), then you will always get the same 'random' numbers out.

                If you want to know more, you can read the following:

                http://www.dreamincode.net/forums/topic/24225-random-number-generation-102/

                http://www.dreamincode.net/forums/topic/29294-making-pseudo-random-number-generators-more-random/

                这篇关于为什么 rand() 每次运行都会产生相同的数字序列?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持跟版网!

                上一篇:rand() 在单个函数中调用时返回相同的值 下一篇:在 C/C++ 中生成服从正态分布的随机数

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