Interacting between two different programs

[Jeremy DeHaan]

I've been toying around with the idea of working on an IDE, 
mostly because I think it would be an interesting/fun project to 
work on. In any case, the only thing I cannot seem to wrap my 
head around is how programs like Code Blocks and Visual Studio, 
and various other IDE's interact with debuggers as if it isn't 
some external thing.

How does someone have one program interact with another like 
this? Can you have one send its output to the other's input? Do 
they somehow share the same IO's? I've never had to write code 
that does anything like this so I'm you great minds out there can 
shed some light.

Thanks in advance!