Why do the answers come out to be different in these two cases where only the integrating order has been changed (The first one comes out to be 0.5 and the other one come out to be -0.5). We have learnt that the limits are interchangeable when the limits are constants. This is a little contradicting.:
P.S. Sorry for the bad English.
Conditions apply to this statement (look up the actual theorem in your book; they should be there). One of those conditions is that the integrals involved should be proper. Your integral is not proper (as the function diverges as we move toward the origin), and therefore strange things may happen in places you didn't expect them to.