/in/foo.c: In function 'change':
/in/foo.c:9:28: error: 'tj' undeclared (first use in this function)
     ty=y[i];y[i]=y[j];y[j]=tj;
                            ^~
/in/foo.c:9:28: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:7:15: warning: variable 'ty' set but not used [-Wunused-but-set-variable]
     double tx,ty;
               ^~
/in/foo.c: In function 'sortq':
/in/foo.c:19:25: warning: unused variable 'keyy' [-Wunused-variable]
     double keyx=x[left],keyy=y[left];
                         ^~~~
/in/foo.c:19:12: warning: unused variable 'keyx' [-Wunused-variable]
     double keyx=x[left],keyy=y[left];
            ^~~~
/in/foo.c:18:16: warning: unused variable 'j' [-Wunused-variable]
     int i=left,j=right;
                ^
/in/foo.c:18:9: warning: unused variable 'i' [-Wunused-variable]
     int i=left,j=right;
         ^
/in/foo.c: In function 'compare':
/in/foo.c:14:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^