Question on getting making sure input is a number

In my program I need the user to input a price. The purchase price must be a number.


My assignment says:
Ignore any data that may be on the life after the amount. In a non-numeric is entered for the price, issue an error message, and ask the user to input the price again.

Does anybody know how to do this? Thank you.

wpr101,

>Does anybody know how to do this?
Short answer? Yes, a great many of us do.

Long(er) answer? We help with problems that you've attempted to solve first yourself, particularly with school assignments.

Let us know what you think about the solution to this problem and we can go from there.

-Skipper

well since it is a float it should ignore any none numeric info after a number is entered I believe.

i was thinking use cin.get (float)? but that would only get one value, or use multiple cin.gets, but then I don't know how long the price is going to be. I've thought it through and still am unsure. Can you help me please?

You might find that reading in a string is easier, since cin will blow up if you say you are reading a float and I enter "I'm a real dummy". If you read in a string and I do enter this, you can do an if check and come right back with

cout<<"As the matter of fact you are, but thats not what I asked. Please try again"<<endl;

and the user will be so Impressed that they will be sure to get it right the second time around.

After all that, you can do a search on google for strtod or stringstream (if you are feeling really adventurous) and see how you can manage to convert a string to a float.

take it as a char array input then check each element of the array to make sure its ASCII code is that of a number with a compound if statement.

If it goes through without finding a non-numerical character, use atof() to convert it to a float, and voila.

Is there an easier way to do it than using arrays? thanks

you might be able to get by with something like this

Code:

int c;
float f;

c = fgetc(stdin);
if (!isdigit(c))
{
       if (c == '.' || c == '-')
       {
              int d = fgetc(stdin);
              if (!isdigit(d))
                     error();
              ungetc(d, stdin);
        }
        else
        {
              error();
        }
}
ungetc(c, stdin);
if (scanf("%f", &f) != 1)
{
        error();
}

you will also probably want to skip white space before
doing it so put in something like

Code:

while(isspace(c = fgetc(stdin)))
        continue;
ungetc(c, stdin);