c a header file realize of multiple .c file

//I write a few variables declaration,then include this head-file in multiple realization-c-file,then appear "multiple definition of 'var1 ' " error

resolution:

　　exists-file:myhead.h,realize1.c,realize2.c,main.c

　　add:myhead.c

　　1.move the defintion-entity-var at myhead.h to myhead.c

　　2.in the myhead.h,announce these var through "extern".