when I try to compile my Arduino UNO sketches using the official latest version Arduino software on Windows 7, I get this error

```
sketch\sketch_may21a.ino.cpp:1:21: fatal error: Arduino.h: No such file or directory
#include <Arduino.h>
                 ^
compilation terminated.
exit status 1
Error compiling for board Arduino/Genuino Uno.

```

what is the solution? What should i do?