C语言 生成随机数 srand用法 伪随机函数rand srand需不需要重新播种问题 srand该不该放在循环里

初接触 rand() 函数

  之前学习了三种排序算法：1.选择排序；2.冒泡排序； 3.插入排序；用三种算法分别对数组里的元素进行排序。一开始对数组初始化时是使用 0 ~ n升序赋值，然后降序排序成 n ~ 0，后来觉得差点意思，为了体现 “真实性”，决定使用 rand() 对数组进行赋值。

  这时还不知道 rand() 是伪随机，只知道它可以 “随机” 数，后来慢慢了解到 rand() 在调用之前需要初始化种子 srand(seed) （就算不初始化，系统也会默认种子 seed 为 1 ），而种子函数 srand() 其实是多个 “随机数序列” 的合集，所以当种子 seed 确定时， 每次程序启动，调用 rand() 所返回的 “随机数序列” 也是确定的。

  _{相同种子下rand()返回的随机数序列}

  例如编写一个程序 randTest ：

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

int main()
{
   
   
	short i;

    srand(1);
    for(i=0; i<1000; i++)
        printf("%d, ", rand());

    return 0;
}

  
  每次编译、运行程序，得到的结果都是相同的。尽管计算机重启、关机，都不会改变种子 seed 为 1 的 rand() 的输出结果：

41, 18467, 6334, 26500, 19169, 15724, 11478, 29358, 26962, 24464, 5705, 28145, 23281, 16827, 9961, 491, 2995, 11942, 4827, 5436, 32391, 14604, 3902, 153, 292, 12382, 17421, 18716, 19718, 19895, 5447, 21726, 14771, 11538, 1869, 19912, 25667, 26299, 17035, 9894, 28703, 23811, 31322, 30333, 17673, 4664, 15141, 7711, 28253, 6868, 25547, 27644, 32662, 32757, 20037, 12859, 8723, 9741, 27529, 778, 12316, 3035, 22190, 1842, 288, 30106, 9040, 8942, 19264, 22648, 27446, 23805, 15890, 6729, 24370, 15350, 15006, 31101, 24393, 3548, 19629, 12623, 24084, 19954, 18756, 11840, 4966, 7376, 13931, 26308, 16944, 32439, 24626, 11323, 5537, 21538, 16118, 2082, 22929, 16541, 4833, 31115, 4639, 29658, 22704, 9930, 13977, 2306, 31673, 22386, 5021, 28745, 26924, 19072, 6270, 5829, 26777, 15573, 5097, 16512, 23986, 13290, 9161, 18636, 22355, 24767, 23655, 15574, 4031, 12052, 27350, 1150, 16941, 21724, 13966, 3430, 31107, 30191, 18007, 11337, 15457, 12287, 27753, 10383, 14945, 8909, 32209, 9758, 24221, 18588, 6422, 24946, 27506, 13030, 16413, 29168, 900, 32591, 18762, 1655, 17410, 6359, 27624, 20537, 21548, 6483, 27595, 4041, 3602, 24350, 10291, 30836, 9374, 11020, 4596, 24021, 27348, 23199, 19668, 24484, 8281, 4734, 53, 1999, 26418, 27938, 6900, 3788, 18127, 467, 3728, 14893, 24648, 22483, 17807, 2421, 14310, 6617, 22813, 9514, 14309, 7616, 18935, 17451, 20600, 5249, 16519, 31556, 22798, 30303, 6224, 11008, 5844, 32609, 14989, 32702, 3195, 20485, 3093, 14343, 30523, 1587, 29314, 9503, 7448, 25200, 13458, 6618, 20580, 19796, 14798, 15281, 19589, 20798, 28009, 27157, 20472, 23622, 18538, 12292, 6038, 24179, 18190, 29657, 7958, 6191, 19815, 22888, 19156, 11511, 16202, 2634, 24272, 20055, 20328, 22646, 26362, 4886, 18875, 28433, 29869, 20142, 23844, 1416, 21881, 31998, 10322, 18651, 10021, 5699, 3557, 28476, 27892, 24389, 5075, 10712, 2600, 2510, 21003, 26869, 17861, 14688, 13401, 9789, 15255, 16423, 5002, 10585, 24182, 10285, 27088, 31426, 28617, 23757, 9832, 30932, 4169, 2154, 25721, 17189, 19976, 31329, 2368, 28692, 21425, 10555, 3434, 16549, 7441, 9512, 30145, 18060, 21718, 3753, 16139, 12423, 16279, 25996, 16687, 12529, 22549, 17437, 19866, 12949, 193, 23195, 3297, 20416, 28286, 16105, 24488, 16282, 12455, 25734, 18114, 11701, 31316, 20671, 5786, 12263, 4313, 24355, 31185, 20053, 912, 10808, 1832, 20945, 4313, 27756, 28321, 19558, 23646, 27982, 481, 4144, 23196, 20222, 7129, 2161, 5535, 20450, 11173, 10466, 12044, 21659, 26292, 26439, 17253, 20024, 26154, 29510, 4745, 20649, 13186, 8313, 4474, 28022, 2168, 14018, 18787, 9905, 17958, 7391, 10202, 3625, 26477, 4414, 9314, 25824, 29334, 25874, 24372, 20159, 11833, 28070, 7487, 28297, 7518, 8177, 17773, 32270, 1763, 2668, 17192, 13985, 3102, 8480, 29213, 7627, 4802, 4099, 30527, 2625, 1543, 1924, 11023, 29972, 13061, 14181, 31003, 27432, 17505, 27593, 22725, 13031, 8492, 142, 17222, 31286, 13064, 7900, 19187, 8360, 22413, 30974, 14270, 29170, 235, 30833, 19711, 25760, 18896, 4667, 7285, 12550, 140, 13694, 2695, 21624, 28019, 2125, 26576, 21694, 22658, 26302, 17371, 22466, 4678, 22593, 23851, 25484, 1018, 28464, 21119, 23152, 2800, 18087, 31060, 1926, 9010, 4757, 32170, 20315, 9576, 30227, 12043, 22758, 7164, 5109, 7882, 17086, 29565, 3487, 29577, 14474, 2625, 25627, 5629, 31928, 25423, 28520, 6902, 14962, 123, 24596, 3737, 13261, 10195, 32525, 1264, 8260, 6202, 8116, 5030, 20326, 29011, 30771, 6411, 25547, 21153, 21520, 29790, 14924, 30188, 21763, 4940, 20851, 18662, 13829, 30900, 17713, 18958, 17578, 8365, 13007, 11477, 1200, 26058, 6439, 2303, 12760, 19357, 2324, 6477, 5108, 21113, 14887, 19801, 22850, 14460, 22428, 12993, 27384, 19405, 6540, 31111, 28704, 12835, 32356, 6072, 29350, 18823, 14485, 20556, 23216, 1626, 9357, 8526, 13357, 29337, 23271, 23869, 29361, 12896, 13022, 29617, 10112, 12717, 18696, 11585, 24041, 24423, 24129, 24229, 4565, 6559, 8932, 22296, 29855, 12053, 16962, 3584, 29734, 6654, 16972, 21457, 14369, 22532, 2963, 2607, 2483, 911, 11635, 10067, 22848, 4675, 12938, 2223, 22142, 23754, 6511, 22741, 20175, 21459, 17825, 3221, 17870, 1626, 31934, 15205, 31783, 23850, 17398, 22279, 22701, 12193, 12734, 1637, 26534, 5556, 1993, 10176, 25705, 6962, 10548, 15881, 300, 14413, 16641, 19855, 24855, 13142, 11462, 27611, 30877, 20424, 32678, 1752, 18443, 28296, 12673, 10040, 9313, 875, 20072, 12818, 610, 1017, 14932, 28112, 30695, 13169, 23831, 20040, 26488, 28685, 19090, 19497, 2589, 25990, 15145, 19353, 19314, 18651, 26740, 22044, 11258, 335, 8759, 11192, 7605, 25264, 12181, 28503, 3829, 23775, 20608, 29292, 5997, 17549, 29556, 25561, 31627, 6467, 29541, 26129, 31240, 27813, 29174, 20601, 6077, 20215, 8683, 8213, 23992, 25824, 5601, 23392, 15759, 2670, 26428, 28027, 4084, 10075, 18786, 15498, 24970, 6287, 23847, 32604, 503, 21221, 22663, 5706, 2363, 9010, 22171, 27489, 18240, 12164, 25542, 7619, 20913, 7591, 6704, 31818, 9232, 750, 25205, 4975, 1539, 303, 11422, 21098, 11247, 13584, 13648, 2971, 17864, 22913, 11075, 21545, 28712, 17546, 18678, 1769, 15262, 8519, 13985, 28289, 15944, 2865, 18540, 23245, 25508, 28318, 27870, 9601, 28323, 21132, 24472, 27152, 25087, 28570, 29763, 29901, 17103, 14423, 3527, 11600, 26969, 14015, 5565, 28, 21543, 25347, 2088, 2943, 12637, 22409, 26463, 5049, 4681, 1588, 11342, 608, 32060, 21221, 1758, 29954, 20888, 14146, 690, 7949, 12843, 21430, 25620, 748, 27067, 4536, 20783, 18035, 32226, 15185, 7038, 9853, 25629, 11224, 15748, 19923, 3359, 32257, 24766, 4944, 14955, 23318, 32726, 25411, 21025, 20355, 31001, 22549, 9496, 18584, 9515, 17964, 23342, 8075, 17913, 16142, 31196, 21948, 25072, 20426, 14606, 26173, 24429, 32404, 6705, 20626, 29812, 19375, 30093, 16565, 16036, 14736, 29141, 30814, 5994, 8256, 6652, 23936, 30838, 20482, 1355, 21015, 1131, 18230, 17841, 14625, 2011, 32637, 4186, 19690, 1650, 5662, 21634, 10893, 10353, 21416, 13452, 14008, 7262, 22233, 5454, 16303, 16634, 26303, 14256, 148, 11124, 12317, 4213, 27109, 24028, 29200, 21080, 21318, 16858, 24050, 24155, 31361, 15264, 11903, 3676, 29643, 26909, 14902, 3561, 28489, 24948, 1282, 13653, 30674, 2220, 5402, 6923, 3831, 19369, 3878, 20259, 19008, 22619, 23971, 30003, 21945, 9781, 26504, 12392, 32685, 25313, 6698, 5589, 12722, 5938, 19037, 6410, 31461, 6234, 12508, 9961, 3959, 6493, 1515, 25269, 24937, 28869, 58, 14700, 13971, 26264, 15117, 16215, 24555, 7815, 18330, 3039, 30212, 29288, 28082, 1954, 16085, 20710, 24484, 2477