How to convert a character array to a floating point without the number rounding itself off?

Question

#include <iostream>
using namespace std;

double toFPV(char str[]);

int main(){

    char numstr [100]= "22.14429789";
    cout<<toFPV(numstr);

    return 0;
}
 double toFPV(char str[]){
    int i = 0;
    double whole = 0;
    double frac = 0;
    int div = 1;
    double num;

    while(str[i]!='.'){
        whole *= 10;
        whole += str[i] - '0';
        i++;
    }

    i++;
    while(str[i]!='\0'){
        frac *= 10;
        frac += str[i]-'0';
        div *= 10;
        i++;
    }
    frac /= div;
    num = whole + frac;
    return num;
}

I'm trying to learn character arrays but I can't figure out what I'm doing wrong. The function toFPV is supposed to convert the character array to a Floating point value but it keeps rounding off the number to four decimal places instead of showing the rest of numbers in the array.