the code you have is way too simplistic. avoid using static values (like 1000) make everything variables from the start.
Initialise all variables when they are declared (or at least before you use them)
e.g. float mp=0.0f,chrg=0;
the interest charge needs to be recalculated every loop on the remaining balance.
There are several ways to do this code, here's one suggestion
as for the improved program...
// add 1.5% to balance
// calculate new balance after payment
// recalculate total payments
// output new balance
// validate new balance
you need to test when a monthly payment will take the balance below zero, break there instead of subtracting, and work out the amount to pay on the last installment to bring the balance to zero.
As this is an excercise i've resisted the temtation to write the whole thing properly. You won't learn anything if people do it for you....