String to double conversion

atof.c

#include<stdio.h>
int main() {
    double sign = 1, intpart = 0, decmod = 1;
    int expsign = 1, exp = 0;
    double ans;
    int i;
    char c;

    c = getchar();
    if (c == '-') {
        sign = -1;
        c = getchar();
    }
    if (c == '+') {
        sign = 1;
        c = getchar();
    }

    while (c >= '0' && c <= '9') {
        intpart = intpart * 10 + c - '0';
        c = getchar();
    }

    if (c == '.') {
        c = getchar();
        while (c >= '0' && c <= '9') {
            intpart = intpart * 10 + c - '0';
            decmod *= 10;
            c = getchar();
        }
    }

    if (c == 'e' || c == 'E') {
        c = getchar();
        if (c == '+') {
            expsign = 1;
            c = getchar();
        }
        if (c == '-') {
            expsign = -1;
            c = getchar();
        }
        while (c >= '0' && c <= '9') {
            exp = exp * 10 + c - '0';
            c = getchar();
        }
    }

    ans = sign * intpart / decmod;
    if (expsign == 1) {
        for (i=0; i<exp; i++)
            ans *= 10;
    } else {
        for (i=0; i<exp; i++)
            ans /= 10;
    }

    printf("%lf\n", ans);
}