I have this code:
double input2;
cout<<"please enter one number:"<<endl;
cin>>input2;
How can I judge if the user input only about digits, like '3', '4', or '4.241'. Sometimes when users enter a character like 'n', '3.q', my program will crash.
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Have a look at this Question it is similar to yours stackoverflow.com/questions/545907/…zero298– zero2982012-11-24 23:33:57 +00:00Commented Nov 24, 2012 at 23:33
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4 Answers
You can use stringstream to convert a string safely to number:
string input;
int mynumber;
cout << "Please enter a valid number: ";
getline(cin, input);
// This code converts from string to number safely.
stringstream myStream(input);
if (myStream >> myNumber)
cout <<"number is valid"<<endl;
else
cout<<"invalid number";
1 Comment
Jagdeep Sidhu
you can find this code at this link on official cplusplus reference site:
cin::<< operator returns NULL if operation went bad. Causes may be many but if interpretation fails then the failbit is set. You can check it with rdstate():
int main()
{
double input2;
cout<<"please enter one number:" << endl;
cin >> input2;
if (cin.rdstate() & ifstream::failbit)
cout << "input badly formatted" << endl;
return 0;
}
Comments
It won't crash because of that. If the cin >> input2 operation fails because of invalid input, cin is put in an invalid state, but it won't crash.
Comments
You need to verify that the input was auccessful
if (std::cin >> input2) {
...
}
.. and if it wasn't deal with the erronous input, e.g.:
std::cin.clear();
std::cin.ignore();
Comments
