Handle Boolean type input

[ryushin]

If i need to check user input of the boolean type input, what is the method to handle it, for other data type i know that infinite loop can be use, but boolean just make me confuse ...

#include<iostream>
using namespace std;
int main()
{
bool i1;
while(true)
  {
   cin>>i1;
   if(i1==1||i1==0)
	break;
  else
	cout<<"Please enter a proper condition(1 to ON/0 to OFF)"<<endl;
  }

return 0;
}

here is my code, when the input or not 1 or 0, it cannot prompt user to to input the i1 again, program just infinite cout the statement(else part), how to handle this input...

[wildblue]

with bool, 0 is false, anything else will be interpreted as true.
I put an output statement into your code below to illustrate - if I enter -5, it is interpreted as true or 1.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

#include<iostream> using namespace std; int main() { bool i1; while(true) { cin>>i1; if(i1==1||i1==0) { cout << "i1 = " << i1 << endl; break; } else cout<<"Please enter a proper condition(1 to ON/0 to OFF)"<<endl; } return 0;

-5 i1 = 1

[ryushin]

so its that possible to handle it?? because when i compile in my visual studio 2012, if i INPUT the value other than 0 or 1, it just keep on infinite loop and print Please enter a proper condition without asking user to enter input again

[wildblue]

I'm not sure why VS is not picking up 1 or 0 as true or false for the bool variable. If I run your code through the C++ shell attached to this site (click the little gear icon at the top right of the code in the post), I don't even get the "Please enter a proper condition".. message if I enter something other than 1 or 0.

If you really wanted to reject integer values other than 1 or 0, I might define i1 as an int instead of a bool.

[ryushin]

my lecturer has request me to use the boolean type...so i have no choice...

[wildblue]

Does the assignment just require that the variable be a bool type, or does it require that they only enter 1 to mean true?


I can't reproduce the infinite loop, but sometimes if the program is not stopping to prompt for input, there's a newline stuck in the buffer which can be taken care of with the cin.ignore() function. Or the input is in a fail state because the type entered doesn't match the variable type, cin.clear() will reset the fail flag.

[Ganado]

Not positive, but I believe an old version of VC++ typedefs a bool to be equivalent to an int or something of that nature, yeah it's weird. Not sure how it is now.

[Duthomhas]

the mistake is in the input: get input as a string (using getline()), then validate it as a name for true or false. That can be as simple as checking that the string is equal to one of "0" and "1".

Hope this helps.

[giblit]

the mistake is in the input: get input as a string (using getline()), then validate it as a name for true or false.

Isn't that effectively the same as doing std::cin >> std::boolalpha >> input;

[Duthomhas]

Yes, with caveats.

Google around boolalpha facets for more.