#include <stdio.h>
#include <ctype.h>
#include <math.h>

#define DEC_SEP X('.') X(',')
#define EXP_SEP X('e') X('E')

double atof(char *s);

int main(int argc, char *argv[])
{
    if (argc < 2) {
        printf("error: expected argument\n");
        return 1;
    }
    printf("%f\n", atof(argv[1]));
    return 0;
}


/* macros for atof */
#define SIGN(s) \
    ((*s == '-') ? (s++, -1) : ((*s == '+') ? (s++, 1) : 1))
#define ATOI(s, x, ...) \
    for (; isdigit(*s); s++, ##__VA_ARGS__) \
        x = 10 * x + (*s - '0')

/* atof: convert string s to double */
double atof(char s[])
{
    double val;

    while (isspace(*s))
        s++;

    /* integer part */
    int sign = SIGN(s);    
    ATOI(s, val);

#define X(sep) *s != sep && 
    if (DEC_SEP 1) return sign * val;
#undef X
    s++;
    /* fractional part */
    int exp = 0; 
    ATOI(s, val, exp--);
    val *= sign * pow(10, exp);

#define X(sep) *s != sep && 
    if (EXP_SEP 1) return val;
#undef X
    s++;
    /* exponent */
    sign = SIGN(s);
    exp = 0;
    ATOI(s, exp);

    return val * pow(10, sign * exp);
}