Integer Tryparse Behavior

I used integer tryparse but today some error came out and found out I was not realizing the function of integer.

int i = -1;
string s = "ab123";
int.TryParse(s, out i);

if (i == -1) {
	// do something
}

This was what I was doing to check if tryParse actually parsed the string or not. But today, I came up with an error something like this..

int i = -1;
string s = input();
int.TryParse(s, out i);
s = s.Trim();
if (s.length == 0 || i == 0) {
	// Error! Input should not be empty or 0!
}

Just to see that if it is 0 or not. But it was actually sending an error when it was not 0. So I realized that even though tryParse does not go through, it would make the integer into 0.

So I changed my code into

string s = input();
s.Trim();
if (int.TryParse(s, int out i) && i == 0) {
	// Error! not supposed to be 0!
}

if (s.length == 0) {
	// Error! not supposed to be empty!
}

and it works.