Can someone explain the bugs in the code samples? The author says they're there but I honestly can't find them.
There's also no null handling here, which was a deliberate omission for clarity. In practice, the convention used inside the VB source code is that null string pointers are semantically the same as empty strings, which introduces some complexities.
Edit: As others have stated, the 'out of bounds' exception should be taken care of by the '\0' at the end of strings in C
You're probably thinking in C# or Java; remember that in C the convention is that a zero char ends strings. If the source string is shorter than the query string then the code will encounter a zero char in the source string at the same time as it encounters a non-zero char in the query string, and the inequality will end the loop before the beyond-bounds dereference.
There are other defects; can you find them?
`starts()` looks like it's not checking if len(source) < len(query), but if, say, query="foobar" and source="foo", when i = 3 the line
if (source[i] != query[i])
return false;
if ('\0' != 'b')
return false;
Always if len(source) < len(query), we'll return false when we get to i=len(source), because source[len(source)] != query[len(source)] as source[len(source)] == '\0' and query[len(source)] != '\0' since len(query) > len(source).