How to merge two data sets with varying date intervals?

I'm sure this problem isn't unique.
I have two sets of data, both $ values and I want to add them together and plot them on a chart.

The problem is that one data set is quarterly and the other is daily but I want to display the resulting set (the addition of the two data sets) in weekly or daily intervals. My sole aim is to be able to add the two data sets and display them as I have described.

The problem I see with this is somehow predicting (I think it's called bootstrapping) the data throughout each quarter so that it will marry up with the daily data.

Critical Point: I don't want to use excel. I need to learn the maths surrounding this as I'm going to program this using C++ and displaying it in a widget chart. As long as I have a method I can do this.

Actually I'm not so sure how to go about any of this so any advice would be well appreciated.

Thanks very much. :confused: