input checking

a quick question I hope...

the input for my program is supposed to be a number, is there an easy way of checking that the input is a number instead of some string of alphabetic characters?

I thought of examing the input a character at a time and use the isdigit() function, but this would be tedious to convert into a floating point number once the validity of the input was verified.

Any help would be greatly appreciated

--kiki--

char bar[10];
fgets(bar, 10, stdin);
double foo = atof(bar);

?