c - 为什么使用C rand()函数如此频繁地显示数字1、2和3？

我想做的是生成一些随机数(不一定是个位数)，例如

然后计算我得到的位数:

count[0] =       3  Percentage =  6.82
count[1] =       5  Percentage = 11.36
count[2] =       6  Percentage = 13.64
count[3] =       3  Percentage =  6.82
count[4] =       6  Percentage = 13.64
count[5] =       2  Percentage =  4.55
count[6] =       7  Percentage = 15.91
count[7] =       5  Percentage = 11.36
count[8] =       3  Percentage =  6.82
count[9] =       4  Percentage =  9.09

这是我正在使用的代码:

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

int main() {

    int i;
    srand(time(NULL));
    FILE* fp = fopen("random.txt", "w");
    // for(i = 0; i < 10; i++)
    for(i = 0; i < 1000000; i++)
        fprintf(fp, "%d\n", rand());
    fclose(fp);

    int dummy;
    long count[10] = {0,0,0,0,0,0,0,0,0,0};
    fp = fopen("random.txt", "r");
    while(!feof(fp)) {
        fscanf(fp, "%1d", &dummy);
        count[dummy]++;
    }
    fclose(fp);

    long sum = 0;
    for(i = 0; i < 10; i++)
        sum += count[i];

    for(i = 0; i < 10; i++)
        printf("count[%d] = %7ld  Percentage = %5.2f\n",
            i, count[i], ((float)(100 * count[i])/sum));

}

如果生成大量随机数(1000000)，则结果如下:

count[0] =  387432  Percentage =  8.31
count[1] =  728339  Percentage = 15.63
count[2] =  720880  Percentage = 15.47
count[3] =  475982  Percentage = 10.21
count[4] =  392678  Percentage =  8.43
count[5] =  392683  Percentage =  8.43
count[6] =  392456  Percentage =  8.42
count[7] =  391599  Percentage =  8.40
count[8] =  388795  Percentage =  8.34
count[9] =  389501  Percentage =  8.36

请注意，1、2和3的匹配次数过多。我已经尝试运行了几次，每次都得到非常相似的结果。

我试图了解什么可能导致1、2和3的出现频率比其他任何数字都高。

从马特·乔纳(Matt Joiner)和帕斯卡·库克(Pascal Cuoq)指出的事情中得出的提示，

我更改了要使用的代码

for(i = 0; i < 1000000; i++)
    fprintf(fp, "%04d\n", rand() % 10000);
// pretty prints 0
// generates numbers in range 0000 to 9999

这就是我得到的(在多次运行中得到类似的结果):

count[0] =  422947  Percentage = 10.57
count[1] =  423222  Percentage = 10.58
count[2] =  414699  Percentage = 10.37
count[3] =  391604  Percentage =  9.79
count[4] =  392640  Percentage =  9.82
count[5] =  392928  Percentage =  9.82
count[6] =  392737  Percentage =  9.82
count[7] =  392634  Percentage =  9.82
count[8] =  388238  Percentage =  9.71
count[9] =  388352  Percentage =  9.71

偏爱0、1和2的原因可能是什么？

谢谢大家。使用

int rand2(){
    int num = rand();
    return (num > 30000? rand2():num);
}

    fprintf(fp, "%04d\n", rand2() % 10000);

我懂了

count[0] =  399629  Percentage =  9.99
count[1] =  399897  Percentage = 10.00
count[2] =  400162  Percentage = 10.00
count[3] =  400412  Percentage = 10.01
count[4] =  399863  Percentage = 10.00
count[5] =  400756  Percentage = 10.02
count[6] =  399980  Percentage = 10.00
count[7] =  400055  Percentage = 10.00
count[8] =  399143  Percentage =  9.98
count[9] =  400104  Percentage = 10.00

最佳答案

rand()生成从0到RAND_MAX的值。在大多数平台上，RAND_MAX设置为INT_MAX，可以是32767或2147483647。

对于上面给出的示例，看来RAND_MAX是32767。对于1到2的值的最高有效位，这将为3，10000和32767设置异常高的频率。您可以观察到，在较小程度上，直到6和7的值也会稍受青睐。

关于c - 为什么使用C rand()函数如此频繁地显示数字1、2和3？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/3381458/