Float variable,but does not read float values!

Please see this simple program:
int main()
{
float number,square_value;
cout<<"Enter a number:";
cin >> number;
square_value=number*number;
cout <<number<<"*"<<number<<"=" <<square_value;
return 0;
}
If I put a float value,e.g. 11.1,it shows the message (on a different window) : Floating Point:square root or negative number.
Would you please any body tell me why?