C - AtoF: Extend AtoF to handle scientific notation of the form 123.45e-6-蒲公英云

C - AtoF: Extend AtoF to handle scientific notation of the form 123.45e-6

r囧r小猫 2022-11-04 05:23 171阅读 0赞

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/*
 * AtoF: Extend AtoF to handle scientific notation of the form 123.45e-6.
 *
 * AtoF_Scientific.c - by FreeMan
 */
#include <stdio.h>
#include <ctype.h>
double AtoF(char s[]);
int main(void)
{
    printf("%f\n", AtoF("123.45e-6"));
}
double AtoF(char s[])
{
    double val, power, base, p;
    int i, sign, exp;
    for (i = 0; isspace(s[i]); i++)
        ;
    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 *= 10.0;
    }
    if (s[i] == 'e' || s[i] == 'E')
    {
        i++;
    }
    else
    {
        return sign * val / power;
    }
    base = (s[i] == '-') ? 0.1 : 10.0; /* 10^(-n) = 1/10^n = (1/10)^n = (0.1)^n */
    if (s[i] == '+' || s[i] == '-')
    {
        i++;
    }
    for (exp = 0; isdigit(s[i]); i++)
    {
        exp = 10 * exp + (s[i] - '0');
    }
    for (p = 1; exp > 0; --exp)
    {
        p = p * base;
    }
    return (sign * (val / power)) * p;
}
// Output:
/*
123.450000
*/