int main(int argc, char **argv) {
    // Read in the command-line arguments and convert the strings to doubles
    double principal = strtod(argv[1], NULL);
    double rate = strtod(argv[2], NULL);

    // Call invest to make you more money
    invest(&principal, rate);

    printf("%.2f\n", principal);
    return 0;
}

void invest(double *principal, double rate){
    *principal = *principal + rate;
}