Date Calculations in crystal 7

Question

I'm a newbie at crystal, and I need to figure out if two dates are within a year of each other. I have one field that's currently a string for grad date, and it's mm/yyyy. Then I have another year that is a parameter field for entering year that is a number yyyy. I need to create a field that looks at the grad date (which is before the entering date), and count the record if it is within one year. So it would be something like [Entering date]-[grad date]<1. But I'm running into all kinds of problems, please help! Thanks.