void wstaw(char * cel, const char * zrodlo, char symbol) {
  unsigned int zrodlo_n = strlen(zrodlo);
  unsigned int offset = 0;
  unsigned int size = zrodlo_n + ceil(zrodlo_n / 3) + 1;

  for (unsigned int i = 0; i < zrodlo_n; i++) {
    cel[i+offset] = zrodlo[i];
    if ((i+1) % 3 == 0) {
      offset++;
      cel[i+offset] = symbol;
    }
  }

  cel[size-1] = '\0';
  for(int k=0;k<size;k++){
    cout<<cel[k]<<endl;}
  }

int main()
{
    char t[]="Ala ma Kota";
    char z[20];
    wstaw(z,t,'x');
    return 0;
}