c dynamic array code example

Example 1: C dynamic array

typedef struct {
  int *array;
  size_t used;
  size_t size;
} Array;

void initArray(Array *a, size_t initialSize) {
  a->array = malloc(initialSize * sizeof(int));
  a->used = 0;
  a->size = initialSize;
}

void insertArray(Array *a, int element) {
  // a->used is the number of used entries, because a->array[a->used++] updates a->used only *after* the array has been accessed.
  // Therefore a->used can go up to a->size 
  if (a->used == a->size) {
    a->size *= 2;
    a->array = realloc(a->array, a->size * sizeof(int));
  }
  a->array[a->used++] = element;
}

void freeArray(Array *a) {
  free(a->array);
  a->array = NULL;
  a->used = a->size = 0;
}

Example 2: allocate memory c

ptr = (castType*)calloc(n, size);

Example 3: C dynamic array

Array a;
int i;

initArray(&a, 5);  // initially 5 elements
for (i = 0; i < 100; i++)
  insertArray(&a, i);  // automatically resizes as necessary
printf("%d\n", a.array[9]);  // print 10th element
printf("%d\n", a.used);  // print number of elements
freeArray(&a);

Example 4: c infiite array

int main(int argc, char *argv[])
   {
       int i;
    
       double* p;    // We uses this reference variable to access
   		     // dynamically created array elements
    
       p = calloc(10, sizeof(double) );  // Make double array of 10 elements
    
       for ( i = 0; i < 10; i++ )
   	  *(p + i) = i;            // put value i in array element i
    
       for ( i = 0; i < 10; i++ )
   	  printf("*(p + %d) = %lf\n", i, *(p+i) );
    
    
       free(p);      // Un-reserve the first array
    
       putchar('\n');
    
       p = calloc(4, sizeof(double) );  // Make a NEW double array of 4 elements    
      
       // ***** Notice that the array size has CHANGED !!! ****

       for ( i = 0; i < 4; i++ )
   	  *(p + i) = i*i;            // put value i*i in array element i
    
       for ( i = 0; i < 4; i++ )
   	  printf("*(p + %d) = %lf\n", i, *(p+i) );
    
       free(p);      // Un-reserve the second array
   }