That error message means that there are bytes in the file that don't correspond to any character the compiler understands, so it's printing out their octal values and telling you that this can't possibly be a valid C(++) program.
The byte sequence you show appears to be the UTF-8 encoding of U+2212 MINUS SIGN. Despite this being the "appropriate" character to use for a minus sign in "proper" Unicode text (which is why it's copying out of a PDF that way), the C family's "basic source character set" remains ASCII-centric; you need to replace each of those minus signs with U+002D HYPHEN-MINUS. Typing over each with a minus sign, as you normally would type it, should do the trick.
