how to make sure input of float is a number

[Mildon]

In the case the user types in a character instead of a number for a float, I put a loop that checks if the value of the float is equal to 0 since if they input a character the value should be 0.

1) From the code, when I type in a letter I get infinite "Error"'s. Why doesn't the second cin ask for input and how can I fix that?

2) In case they really DO type in 0 it will still give error, although not infinite errors for some reason. Is there a different way to make sure the value of the input is not equal to a letter to bypass this problem?

#include <iostream>

using namespace std;

int main(){
    int reset = 1;
    float value1;

    while(reset == 1){
        cout << "Enter a number: ";
        cin >> value1;
        if(value1 == 0){
            cout << "Error";
            cin >> value1;
        } else {
            reset = 0;
        }
    }
}

[RadWayne]

Hopefully this helps:

http://www.cplusplus.com/forum/beginner/26821/

[giblit]

If you want to ensure it is a floating point instead of just a normal integer you may have to read everything into a string and parse it to see it has correct format using std::getline and std::stringstream

[Void life]

You need to clear error state of the input and also the remove the bad input to avoid getting an infinite loop of Errors. You can do something like this to check. This is an easy way to check for bad input

if (cin.fail()) //checking whether failbit or badbit is set
    {
        cout<<"error";
        cin.clear(); //sets a new value for the stream's internal error state flags.
        cin.ignore(numeric_limits<streamsize>::max(),'\n'); //ignores rest of the input ..
    }

But if you want to completely ensure that it is a number you need to do as giblit suggested and do something like this

int only_int(const char *output)//To checking if input is integer
{
    int check;
    string user_input;
    cout<<output<<endl;
    while(1)
    {
        getline(cin,user_input);//gets user input as a string
        stringstream convert(user_input);//makes string into a stream
        if(convert >> check &&!(convert >> user_input))//checking for valid conversion and any rejects if any unconverted input left
        {
            return check;
        }
        else
        {
           cin.clear();
           cout<<"ERROR!\nwrong input\nPlease enter a NATURAL NUMBER only"<<endl;
        }
    }
}

[giblit]

if (cin.fail()) //checking whether failbit or badbit is set you should use if(!cin)

[Void life]

what difference does it make?

[giblit]

I suppose none. It's just less verbose and more common. Also, I tend to keep one style instead of using two styles. You use the fail method then the operator ! method later on.

[Void life]

ah i see.. well im still relatively new to programming , so yeah i tend to mix and match stuff :)
thanks

[Mildon]

Thanks, this takes away the looping error work.

cin.clear();
cin.ignore();

However I don't understand the second part. I tried to write this

string input;
cin>>input;
getline(cin, input);
stringstream convert(input);

But it gave me : error: variable 'std::stringstream convert' has initializer but incomplete type.

How do I give it a complete type?

[Void life]

you need to #include <sstream> sorry probably should have mentioned that. I think thats your problem if that doest fix it post your whole code

[giblit]

Also you don't need the cin >> input if you are using getline and also you want to avoid using getline after [/code]cin >>[/code] since the latter leaves a newline in the buffer if you wish to use it like that you are going to need to ignore the newline(and possibly other things) left in the buffer. std::cin.ignore(1024, '\n'); //or std::numeric_limits<std::streamsize>::max() instead of 1024