C++11：全WA，麻烦个位dalao神犇帮助帮助，本蒟蒻在此愿听指教

#include <bits/stdc++.h>
using namespace std;
int main()
{
	int T;
	cin >> T;
	int a,p;
	for (int i = 1; i <= T; i++)
	{
		cin >> a >> p;
		if (p < 16) a -= 10;
		if (p > 20)
		{
			for (int j = 20; j < p; j++) a--;
		}
		if (a == 0)
		{
			cout << 0 << endl;
			continue;
		}
		cout << a << endl;
	} 
	return 0;
}