0

```
An ISBN (International Standard Book Number) identifies a unique publication. An ISBN is ten digits. The first nine digits must be decimal digits (0...9). The tenth may a decimal digit or the letter X, according to the checksum, discussed below. Three single dashes may be between any of the characters, but an ISBN must not begin or end with a dash.
Some example ISBNs:
0-201-88337-6
0-13-117334-0
0821211315 (no dashes ok)
1-57231-866-X
The last character of an ISBN number is a checksum. The checksum is the determined by the first 9 digits; it is computed by taking modulo 11 (the remainder after dividing by 11) of the sum of each digit multiplied by its position in the ISBN. The letter X corresponds to a value of 10.
Here are two ISBNs and the calculations that show how the check sum is determined:
0-201-88337-6 -> (0*1 + 2*2 + 0*3 + 1*4 + 8*5 + 8*6 + 3*7 + 3*8 + 7*9) mod 11 = 6
1-57231-866-X -> (1*1 + 5*2 + 7*3 + 2*4 + 3*5 + 1*6 + 8*7 + 6*8 + 6*9) mod 11 = 10 (X)
For more info, check out:
www.isbn.org
www.amazon.com Try a book search by ISBN
Some invalid ISBNs:
0-201-8A337-6 (bad digit)
0-201-88337-63 (too many digits)
0-201-88-337-6 (too many dashes)
0-201883376 (not enough dashes)
0-201-88337-3 (wrong check sum)
-013-117334-0 (beginning or ending dash)
157231--866-X (sequential dashes)
013-1134-0 (too few digits)
Write a menu driven program that will verify ISBNs either from user input or from file input (use default filename = isbntest.txt). The file format should be:
integer value that specifies the number of ISBN's to follow (max of 20),
ISBN, (one ISBN per line)
ISBN, etc.
Example data file:
6
0-201-88337-6
0-13-117334-0
157231--866-X
-013-117334-0
0821211315
1-57231-866-X
```

can somebody simplify for me what the problem is and some advise to solve it because of my English, I don't really know what itreally means.thank you