Question

想将char * array改组并使元素随机排序

我尝试

const char *words = { "one", "two", "three", "four", "five", "six" }; 
for (int i=0; i<6; i++)
{
    int r = (rand() % (6 - i)) + i;

    int temp =  words[i];
    words[i] = words[r];
    words[r] = temp;
}

虽然在迭代数组单词时出错

请解释

Answer 1

如前所述，您有几个问题

const char *words = { "one", "two", "three", "four", "five", "six" };

无效，因为初始化（以及代码的其余部分）表明 words 是一个数组，因此将其替换为

const char *words[] = { "one", "two", "three", "four", "five", "six" };

    int temp =  words[i];
    words[i] = words[r];
    words[r] = temp;

单词是const char *的数组，因此 temp 不能是 int ，请使用

const char * temp = words[i];

除此之外

使用文字 6 是危险的，请使用 sizeof 考虑对单词的任何更改，用sizeof(words)/sizeof(*words)替换6
正确的索引类型是size_t，
为了不具有始终相同的执行力，例如，将 srand 与当前时间一起使用

例如：

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

int main(void)
{
  const char *words[] = { "one", "two", "three", "four", "five", "six" };
  const size_t nelts = sizeof(words)/sizeof(*words);

  srand(time(NULL));

  for (size_t i=0; i < nelts;  ++i)
  {
    size_t r = (rand() % (nelts - i)) + i;
    const char * temp =  words[i];

    words[i] = words[r];
    words[r] = temp;
  }

  /* show */
  for (size_t i=0; i < nelts;  ++i)
    puts(words[i]);

  return 0;
}

编译和执行：

pi@raspberrypi:/tmp $ gcc -pedantic -Wall -Wextra c.c
pi@raspberrypi:/tmp $ ./a.out
four
one
two
five
three
six
pi@raspberrypi:/tmp $ ./a.out
one
three
two
four
five
six
pi@raspberrypi:/tmp $ ./a.out
six
five
two
four
three
one
pi@raspberrypi:/tmp $ ./a.out
three
one
five
four
six
two

Answer 2

OPs代码中存在多个错误和缺陷。

字符串数组：

const char *words = { "one", "two", "three", "four", "five", "six" };

不确定编译器如何读取（如果没有抱怨的话）。 C字符串数组应为：

const char *words[] = { "one", "two", "three", "four", "five", "six" };

幻数

for (int i=0; i<6; i++)

6是magic number，被认为是不良样式。最好给它起个名字。更好的是：该值可以由编译器确定，这可以提高代码的可维护性：

int n = sizeof words / sizeof *words;
for (int i = 0; i < n; ++i) {

rand()

int r = (rand() % (6 - i)) + i;

rand()是具有某些限制的伪随机生成器。不应与% n一起使用。对于某些n（例如2），这可能会导致出现相当不随机的序列。 cppreference文档。 rand()的例子给出了一个更好的示例，我将其转换为函数：

int randomRange(int min, int max)
{
  for (int range = max - min;;) {
    int x = min + rand() / ((RAND_MAX + 1u) / range);
    if (x < max) return x;
  }
}

被称为

int r = randomRange(i, n);

惯用调换

int temp =  words[i];

如果要交换的数组元素的类型为const char*，则temp也必须为：

    const char *temp = words[i];
    words[i] = words[j];
    words[j] = temp;

完整的示例代码：

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

int randomRange(int min, int max)
{
  for (int range = max - min;;) {
    int x = min + rand() / ((RAND_MAX + 1u) / range);
    if (x < max) return x;
  }
}

int main(void)
{
  /* an array of strings */
  const char *words[] = { "one", "two", "three", "four", "five", "six" };
  /* let compiler determine size */
  int n = sizeof words / sizeof *words;
  /* shuffle */
  for (int i = 0; i < n; ++i) {
    int j = randomRange(i, n);
    /* idiomatic swap */
    const char *temp = words[i];
    words[i] = words[j];
    words[j] = temp;
  }
  /* print result */
  const char *sep = "";
  for (int i = 0; i < n; ++i) {
    printf("%s%s", sep, words[i]);
    sep = ", ";
  }
  /* done */
  return 0;
}

输出：

six, three, one, two, four, five

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C随机播放2D数组

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