麻烦看一下这个程序为什么不能输出

#include <iostream>
#include <fstream>
using namespace std;

int main()
{
	char a[80]{};
	char b[80]{};
	char c[80]{};

	cout << "请输入字符串a：\n";
	cin >> a;
	cout << "请输入字符串b：\n";
	cin >> b;

	int k = 0;
	for (int i = 0; a[i]; i++)
	{
		for (int j = 0; b[j]; j++)
		{
			if (a[i] == b[j])
			{
				c[k] = b[j];
				k++;
				break;
			}
		}
	}

	if (k == 0)
	{
		cout << "无重复字符！";
		return -1;
	}

	for (int tmp, i = 0; i < k - 1; i++)
	{
		if (c[i] < c[i + 1])
		{
			tmp = c[i];
			c[i] = c[i + 1];
			c[i + 1] = tmp;
		}
	}

	ofstream outfile;
	outfile.open("filec.txt");

	cout << "共有字符:\n";
	cout << c;
	outfile << c;
	outfile.close();

	return 0;
}