Exercise 4-2: atof with scientific notation

Extend atof to handle scientific notation of the form

123.45e-6

where a floating-point number may be followed by e or E and an optionally signed exponent.

/* atof:  convert string s to double */
double atof(char s[])
{
    double val, power;
    int i, sign;

    for (i = 0; isspace(s[i]); i++)  /* skip white space */
        ;
    sign = (s[i] == '-') ? -1 : 1;
    if (s[i] == '+' || s[i] == '-')
        i++;
    for (val = 0.0; isdigit(s[i]); i++)
        val = 10.0 * val + (s[i] - '0');
    if (s[i] == '.')
        i++;
    for (power = 1.0; isdigit(s[i]); i++) {
        val = 10.0 * val + (s[i] - '0');
        power *= 10;
    }
    return sign * val / power;
}

Each input line holds one number. Print atof of it with printf("%g\n", ...).