/in/foo.c: In function 'main':
/in/foo.c:7:21: error: 'a' undeclared (first use in this function)
  num=find(xmin,xmax,a);
                     ^
/in/foo.c:7:21: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:11:3: error: expected ';' before 'printf'
   printf("\n");
   ^~~~~~
/in/foo.c: In function 'find':
/in/foo.c:16:10: warning: variable 'x' set but not used [-Wunused-but-set-variable]
  int i,j,x,num=0;
          ^
/in/foo.c:16:8: warning: unused variable 'j' [-Wunused-variable]
  int i,j,x,num=0;
        ^