C 编程数组元素的平均值

Question

If the array element is twice as large as its predecessor (for example 1,2,3,4,.. in this case element 2 is twice as large as element before 2, which is 1) then program should make average value of these two elements (in this case 1 + 2 = 3, 3/2 = 1.5) and after making average value, program should put that value between these two numbers and print new array. (in this case new array would look like: 1, 1.5, 2, 3, 4, ...) Do you have any idea how to make this? Array consists of double numbers.

#include <math.h>
#include <stdio.h>
#define epsilon 0.0001
int main() {
  int i, k = 0, n;
  double arr[100];
  do {
    printf("Enter number of array elements: ");
    scanf("%d", &n);
  } while (n <= 0 || n > 100);
  printf("Enter array: ");
  for (i = 0; i < n; i++) {
    scanf("%lf", &arr[i]);
  }
  for (i = 0; i < n; i++) {
    if (fabs(arr[i + 1] - 2 * arr[i]) < epsilon) {
     
    }
  }
  return 0;
}

Answer 1

I think you need just check if next element is at least twice as large as previous and then print additional number in a sequence.

int main() {
  int i, k = 0, n;
  double arr[100];
  do {
    printf("Enter number of array elements: ");
    scanf("%d", &n);
  } while (n <= 0 || n > 100);
  printf("Enter array: ");
  for (i = 0; i < n; i++) {
    scanf("%lf", &arr[i]);
  }
  printf("%f ", arr[0]);
  double med = 0;
  for (i = 0; i < n - 1; i++) {
    if (arr[i+1] >= 2 * arr[i]) {
      med = (arr[i + 1] + arr[i]) / 2;
      printf("%f ", med);
    }
    printf("%f ", arr[i+1]);
  }
  return 0;
}

Answer 2

To address comments suggesting how to create array at runtime ...

(and a few other suggestions are in comments in code below.)

Rather than creating an array with set size, create one with the number of elements decided by user by using a VLA . It is a form of dynamically placing an array into stack (as opposed to heap) memory , as such, it does not require use of calloc() et.al. so no need to call free() Example using your original code:

int main(void) {//main() is not a prototyped signature of main. Use void parameter.
  int i = 0 /*k = 0*/, n;//k is not used, init i

//double arr[100] = {0};//better to initialized before using
                    //and even better to use VLA (if using C99 or newer.)
  do {
        if(i++ > 3) {//prevent infinite loop possibility
           printf("%s", "Exiting\n"); 
           return 0;    
        }
        printf("Enter number of array elements: ");
        scanf("%d", &n);
  } while (n <= 0 || n > 100);
  double arr[n];//Variable Length Array (VLA)
  memset(arr, 0, sizeof arr);/initialize to zero
  ...

Be sure to read the VLA link above, as VLA does have its caveats, but will work fine in the case of your code.