C - How to merge two sequences (array) into one without repeating numbers?

Question

C++ / C#

// задача 338б

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

#define SIZE 25

int n, a[SIZE], *b, *c;

int getArraySize(int *arrayName) {
  if (arrayName != NULL)
    return sizeof(arrayName) / sizeof(arrayName[0]);
  else {
    printf("ERROR");
    return 0;
  }
}

void main() {
  n = 0 + rand() % ((100 + 1) - 0);
  b = (int*)malloc(sizeof(int)*n);
  c = b;


  for (int i = 0; i< SIZE; i++) {
    a[i] = 0 + rand() % ((100 + 1) - 0);
  }
  for (int i = 0; i< n; i++) {
    b[i] = 0 + rand() % ((200 + 1) - 0);
  }


  for (int i = 0; i< SIZE; i++) {
    printf("> %d. %d\n", i, a[i]);
  }
  printf("\n");
  for (int i = 0; i< n; i++) {
    printf(">> %d. %d\n", i, b[i]);
  }


  for (int i = 0; i<SIZE; i++) {
    for (int j = 0; j<n; j++) {
      if (a[i] != b[j]) {
        c = (int*)realloc(c, sizeof(int)*(n + 1));
        c[getArraySize(c)] = a[i];
      }
    }
  }
  printf("pause");

  for (int i = 0; i<getArraySize(c); i++) {
    printf(">>> %d. %d ", i, c[40]);
  }
  system("pause");
}

This code outputs two sequences without interacting with the third one. Help fix the bugs please

Answer 1

With the construct:
return sizeof(arrayName) / sizeof(arrayName[0]);
you won't get the array size for dynamic arrays, this only works for static arrays when the compiler knows the array size in advance. The sizeof() operation is executed at compile time.
You must manually read the size of the array c and increase it with realloc.