C++ vector<int>::size_type的使用

int main()
{
vector<int> vcDatas;

int word;
int k = 0;
while(k != 5)
{
++k;
cin >>word;
vcDatas.push_back(word);
}

for (vector<int>::size_type size_x = 0; size_x != vcDatas.size(); ++size_x)
{
cout << vcDatas[size_x] << endl;
}

int wait;
cin >> wait;

return 0;
}