Comment vérifier si l'entrée est numérique (flottante) ou est un personnage?

Voici le code non testé pour vérifier si une chaîne répond à la spécification demandée.

#include <ctype.h>


/*  IsFloatNumeral returns true (1) if the string pointed to by p contains a
    valid numeral and false (0) otherwise.  A valid numeral:

        Starts with optional white space.
        Has an optional hyphen as a minus sign.
        Contains either digits, a period followed by digits, or both.
        Ends with optional white space.

    Notes:

        It is unusual not to accept "3." for a float literal, but this was
        specified in a comment, so the code here is written for that.

        The question does not state that leading or trailing white space
        should be accepted (and ignored), but that is included here.  To
        exclude such white space, simply delete the relevant lines.
*/
_Bool IsFloatNumeral(const char *p)
{
    _Bool ThereAreInitialDigits = 0;
    _Bool ThereIsAPeriod = 0;

    //  Skip initial spaces.  (Not specified in question; removed if undesired.)
    while (isspace(*p))
        ++p;

    //  Allow an initial hyphen as a minus sign.
    if (*p == '-')
        ++p;

    //  Allow initial digits.
    if (isdigit(*p))
    {
        ThereAreInitialDigits = 1;
        do
            ++p;
        while (isdigit(*p));
    }

    //  Allow a period followed by digits.  Require at least one digit to follow the period.
    if (*p == '.')
    {
        ++p;
        if (!isdigit(*p))
            return 0;
        ThereIsAPeriod = 1;
        do
            ++p;
        while (isdigit(*p));
    }

    /*  If we did not see either digits or a period followed by digits,
        reject the string (return 0).
    */
    if (!ThereAreInitialDigits && !ThereIsAPeriod)
        return 0;

    //  Skip trailing spaces.  (Not specified in question; removed if undesired.)
    while (isspace(*p))
        ++p;

    /*  If we are now at the end of the string (the null terminating
        character), accept the string (return 1).  Otherwise, reject it (return
        0).
    */
    return *p == 0;
}