old school string to number convert

#include <iostream>
#include <cstring>

using std::cout;
using std::endl;

// convert string to double old school
double convert(char * s) {
        int i=0;
        double intPart = 0, fracPart = 0;
        while(s[i]!='.') {
                intPart = intPart*10 + (s[i]-'0');
                i++;
        }
        i = strlen(s)-1;
        while(s[i]!='.') {
                fracPart = (fracPart + (s[i]-'0'))/10;
                i--;
        }
        double conversion = intPart + fracPart;
        return conversion;
}

int main() {

        cout << convert("3.14159") << endl;
        return 0;
}