confused on results

[metulburr]

I am confused on why while (! (cin >> num_grade)) would be false on the condition the input was not a number, being num_grade as type int?

#include <iostream>
#include <string>

using namespace std;

bool check(int grade, int low, int high){
	if (grade >= low && grade <= high)
		return (true);
	else
		return (false);
}

char num_to_ch(int grade){
	if (check(grade, 0, 59))
		return 'F';
	else if (check(grade, 60, 69))
		return 'D';
	else if (check(grade, 70, 79))
		return 'C';
	else if (check(grade, 80, 89))
		return 'B';
	else if (check(grade, 90, 100))
		return 'A';
        else
	        return 'x';
}

int main(){
	string error = "That is invalid input";
	int num_grade;
	char grade;
	
	cout << "Enter grade in number [0-100]" << endl;

	while (! (cin >> num_grade) || num_grade < 0 || num_grade > 100){
		cout << error << endl;
		cin.clear();
		cin.ignore(1000, '\n');
	}
	grade = num_to_ch(num_grade);
	cout << grade;
}

[jlb]

Because the C++ extraction operator>> knows that a numeric value requires a numeric input. If it doesn't get a valid input then there was an error reading the stream, hence the proper error flag was set.

[metulburr]

ok i didnt know that it has the ability to do that by itself, thanks.