# Checking Floats

• 04-29-2011
ScottyBoy
Checking Floats
How would I go about checking to see if a cin >> input is a number/float? I'm making a really basic calculator, which works fine, unless you put in letters or symbols. Then you get some really funky results. LOL

Here's what I have so far:
Code:

```#include <iostream> #include <string> using namespace std; int main () {         string action;         float f_n;         float s_n;                 cout << "\n\n What do you want to do? (Possible answers: multiply, add, subtract, divide) \n";         cin >> action;                 if (action != "add" && action != "subtract" && action != "multiply" && action != "divide")         {                 cout << "Unknown action command.";                 return 1;         }                 cout << "\n\n First Number \n";         cin >> f_n;                 // Somehow check to see if "f_n" is an int/float....                cout << "\n\n Second Number \n";         cin >> s_n;                 // Somehow check to see if "s_n" is an int/float....                 if (action == "add")         {                 cout << "Your answer is >> " << f_n + s_n << " \n\n";         }         else if (action == "subtract")         {                 cout << "Your answer is >> " << f_n - s_n << " \n\n";         }         else if (action == "multiply")         {                 cout << "Your answer is >> " << f_n * s_n << " \n\n";         }         else if (action == "divide")         {                 cout << "\n\n Your answer is >> " << f_n / s_n << " \n\n";         }         else         {                 cout << "\n\n unknown operation" << " \n\n";                 return 1;         }         return 0; }```
• 04-29-2011
laserlight
Check the result of cin >> f_n.
• 04-29-2011
ScottyBoy
And how do I do that? That's kinda what I was asking. Thanks for your help, BTW. :)
• 04-29-2011
laserlight
It could be along the lines of:
Code:

```if (!(cin >> f_n)) {     cout << "Invalid input" << endl;     // exit program here? }```
• 04-29-2011
grumpy
If you check documentation for stream objects, you will find they support an operator!() which gives the error state. If an istream is in an error state after attempting to read a float, a float has not been successfully read in. Note that any error state will need to be cleared before attempting to read anything else.
• 04-29-2011
ScottyBoy
Okay, thanks, peeps. I'll check the documentation, and see where I get with that. If its anything like the PHP manual, I'm all set with reading for the next six months. XD