“Cannot be resolved to a type” this message is probably the most annoying in Eclipse. It is caused by its Indexer which goes crazy if we forget to choose appropriate tool chain during creating or importing a new project. As a result Eclipse can’t find the system headers like stdint.h
You could find many advices on the Internet which may not work in case this error, e.g index rebuilding, project refreshing, tool chain changing etc. You can add missing paths to C/C++ General -> Paths and Symbols -> Includes manually but the fastest method is to import project again and set appropriate Tool Chain.