# 7.6. A run-time error¶

Way back in Section [run-time] I talked about run-time errors, which are errors that don’t appear until a program has started running.

So far, you probably haven’t seen many run-time errors, because we haven’t been doing many things that can cause one. Well, now we are. If you use the [] operator and you provide an index that is negative or greater than length-1, you will get a run-time error and a message something like this:

index out of range: 6, string: banana


Try it in your development environment and see how it looks.

Running the active code below will result in a runtime error. Can you fix it so that we print out the first letter and last letter of string greeting instead of indexing out of range?

Construct a block of code that correctly changes the string to say “cat in the hat” instead of “cat on the mat”, then print it.