Final answer:
The index of the last character in a string that has 10 characters is 9 due to zero-based indexing, where counting starts from 0.
Step-by-step explanation:
If a string has 10 characters, the index of the last character would be 9. This is because most programming languages use zero-based indexing. In zero-based indexing, the first character is at index 0, so the last character of a 10-character string would logically be at the 9th position (i.e., 10-1).
For example, if you have a string 'ABCDEFGHIJ', and you want to access the last character 'J', in most programming languages you would write string[9] to get the correct character.