can't run ; error compiling board for example sketch.

Development Tools IDE 1.x
1

Arduino: 1.8.5 (Windows 10), Board: "Arduino/Genuino Uno"

c:/users/new user/desktop/arduino/hardware/tools/avr/bin/../lib/gcc/avr/4.9.2/../../../../avr/lib/avr5/crtatmega328p.o:(.init9+0x0): undefined reference to `main'

collect2.exe: error: ld returned 1 exit status

exit status 1
Error compiling for board Arduino/Genuino Uno.

This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.

2

Please restart the Arduino IDE. That will clear the cache, which hopefully will make the problem go away.