Question

我想用loop创建一个数组。如果我不知道我将如何创建它的大小。当我不知道有多少数组元素的用户会给出输入我将会那么

#include <stdio.h>
int main()
{
    int n,j;
    int arr[n];
    for(j=0;j<n;j++)
    {
        scanf("%d",&arr[j]);
    }
    return 0;
}

Answer 1

您需要扫描n。

的值

int n,j; 
scanf("%d", &n);
int arr[n];

了解variable length arrays。

您可以使用realloc来增加尺寸。

int *arr = NULL;
int j = 0;
do{
    arr = realloc(arr, j+1);
}while(scanf("%d", arr[j++]) == 1)

Answer 2

如果您不知道要读取的值的数量，则必须动态分配一些内存，然后在需要时分配更多内存，最后解除分配不再使用的任何内容。

您还需要检查scanf的返回值，以确定何时停止循环。这是一个例子。

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

int main() {
// You could reallocate to allow for one extra item at a time, an
// fixed chunk at a time (as shown here), or some other strategy such
// as doubling the allocation size at each realloc
#define CHUNK_SIZE 20

  int n = 0, n_chunks = 0;
  int *arr = 0;

  do {
    if (n == (n_chunks * CHUNK_SIZE)) {
      ++n_chunks;
      arr = realloc(arr, sizeof arr[0] * n_chunks * CHUNK_SIZE);
       if (!arr) { return 1; } // Memory allocation can fail, so check it
    }

  } while (1 == scanf("%d", &arr[n]) && ++n);

  // Trim any excess
  arr = realloc(arr, sizeof arr[0] * n);
  if (!arr && n > 0) { return 1; }

  // Print the values we read in
  printf("Read %d value%s\n", n, (n == 1) ? "" : "s");
  for (int x = 0; x < n - 1; ++x) {
    printf("%d,", arr[x]);
  }
  if (n > 0) { printf("%d\n", arr[n - 1]); }

  // At the end of the program, free the memory we allocated
  free(arr);
  arr = 0;
  return 0;
}

Answer 3

最简单的方法是使用scanf（）查找用户输入，然后将结果设置为变量。为清楚起见，我经常将数组大小变量设置为arraysize，然后将其设置为int i = arraysize，这样如果我执行某种条件循环，则更容易阅读。例如（在您的问题中使用for()循环：

#include <stdio.h>

int main(void)
{
    int arraysize, i;

    printf("Please input an array size.\n");
    scanf("%d", &arraysize); //Will set the user input and use it as array size
    getchar(); 
    i = arraysize; //This is for sheer convenience in the for() loop
    int array[i]; //This creates an array of the size inputted by the user
    printf("Please input %d numbers to fill the array.\n", i); 
    for(i = 0; i<arraysize; i++) //Has the user put in a number for every space in the array
    {
         scanf("%d", &array[i]); //The i coordinate updates with the i++
         getchar();

    }
    printf("Your numbers were: \n");
    for(i = 0; i<arraysize; i++) //Same thing as the previous for() loop
    {                            //except we are printing the numbers in the table
         printf("| %d |", array[i]);

    }
}

输出如下：

[PROGRAM BEGINS]
Please input an array size.
5
Please input 5 numbers to fill the array.
1 2 33 4 5
Your numbers were:
| 1 || 2 || 33 || 4 || 5 |
[PROGRAM ENDS]

希望有所帮助！

如何在数组大小未知时创建数组

3 个答案: