C++ Exception handling Inside loop not working [duplicate] - c++

Question

I am just trying to write a simple program that reads from cin, then validates that the input is an integer. If it does, I will break out of my while loop. If not, I will ask the user for input again.
My program compiles and runs just fine, which is great. But it doesn't prompt for new input if I enter a non numeric value. What gives?
#include <iostream>
using namespace std;
int main() {
bool flag = true;
int input;
while(flag){
try{
cout << "Please enter an integral value \n";
cin >> input;
if (!( input % 1 ) || input == 0){ break; }
}
catch (exception& e)
{ cout << "Please enter an integral value";
flag = true;}
}
cout << input;
return 0;
}

Answer 1

C++ iostreams don't use exceptions unless you tell them to, with cin.exceptions( /* conditions for exception */ ).
But your code flow is more natural without the exception. Just do if (!(cin >> input)), etc.
Also remember to clear the failure bit before trying again.
The whole thing can be:
int main()
{
int input;
do {
cout << "Please enter an integral value \n";
cin.clear();
cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
} while(!(cin >> input));
cout << input;
return 0;
}

Answer 2

Don't use using namespace std; Instead import what you need.
It's better to do input a line at a time. This makes behavior much more intuitive if you have multiple words on one line, or if you press enter before typing anything.
#include <iostream>
#include <sstream>
#include <string>
using std::cerr;
using std::cin;
using std::cout;
using std::endl;
using std::flush;
using std::getline;
using std::istringstream;
using std::string;
int main() {
int input;
while (true)
{
cout << "Please enter an integral value: " << flush;
string line;
if (!getline(cin, line)) {
cerr << "input failed" << endl;
return 1;
}
istringstream line_stream(line);
char extra;
if (line_stream >> input && !(line_stream >> extra))
break;
}
cout << input << endl;
return 0;
}