Hiya,
A couple of observations:
1. If you're reading in the amount each time why do you have cin>>amount in each case statement? Cant you just call this between lines 17 and 18?
2. These variables: debA, credA, debB, credB, debC, credC are all uninitialised. So if you add a number to a variable holding a random value, then you ain't gonna get a number you're expecting.