There are a number of functions in the atoi() family, some of which can be used for floating point values. These functions are strtof(), strtod(), and strtold(). Don't use atoi() or atof() functions - it is better to use strtol() and strtof() type functions instead as they give you better support when parsing input. If you are running Unix/Linux systems, see the man pages. If Windows, see the MSDN library documentation, or look up online.
Yes, well your example is treating a char as an integer, which it is (a really short one). That really isn't what the original question was about, as far as I could see. It seemed to be about converting a character representation of a number (a string) to a real number, hence the comments about using atoi(), stroul(), etc. Next time, be more precise.