I think you have misunderstood the quesstion. You are supposed to enter numbers and stop when −1 is entered. You want a loop for the input with ... while (input != -1) ... in. You need a separate function for reversing the digits in the number.
Warning: 567890 will reverse to 98765, and if you reverse that again you will get 56789, not the original number.
Please don't quote the whole of a preceding post; that adds nothing new and is liable to removal without notice.
Start by writing a program that takes entry of a number and simply prints, “You entered 123456.” When that is working correctly, you can enhance it by adding more functionality.