C Simple example Example of finding the time it takes to double the principal with compound interest. While the door is weird.

int years = 0;
double rate, investment;

printf ("Principal :");
scanf("%f", &investment);
printf ("Rate :");
scanf("%f", &rate);

double total = investment;

while (total < investment * 2)
{
    total = total * (1 + rate);
    years += 1;
}
printf("%d years";

return 0;