#include<stdio.h>
#include<conio.h>
#include<math.h>
#define MAX 100

void nhap (int a[], int &n)
{
	do
	{
		printf("\nNhap so phan tu: ");
		scanf("%d", &n);
		if(n <= 0 || n > MAX)
		{
			printf("\nSo phan tu khong hop le. Xin kiem tra lai !");
		}
	}while(n <= 0 || n > MAX);
	for(int i = 0; i < n; i++)
	{
		printf("\nNhap a[%d]: ", i);
		scanf("%d", &a[i]);
	}
}

void xuat(int a[], int n)
{
	for(int i = 0; i < n; i++)
	{
		printf("%4d", a[i]);
	}
}

int KiemTraDang3K(int n)
{
	int flag=1;
    n = n < 0 ? -n : n;
    if(n < 2)
        return 1;

	while(n > 1)
	{
		int du = n % 3;
		if(du != 0)  // nếu dư mà khác 0. lập tức báo sai
			flag = 0;
		n /= 3;
	}
	if(flag == 1)
      return 1;
    else
      return 0;
}

void LietKeCacGiaTriCoDang3K(int a[], int n)
{
	for(int i = 0; i < n; i++)
	{
		if(KiemTraDang3K(a[i]) == 1)
		{
			printf("%4d", a[i]);
		}
	}
}
int main()
{
	int n;
	int a[MAX];

	nhap(a, n);
	xuat(a, n);
	printf("\nCac gia tri co dang 3^k trong mang la: ");
	LietKeCacGiaTriCoDang3K(a, n);

	getch();
	return 0;
}

Line 17: error: conio.h: No such file or directory
Line 6: error: expected ';', ',' or ')' before '&' token
In function 'xuat':
Line 26: error: 'for' loop initial declaration used outside C99 mode
In function 'LietKeCacGiaTriCoDang3K':
Line 54: error: 'for' loop initial declaration used outside C99 mode