/in/foo.c: In function 'main':
/in/foo.c:7:8: error: 'i' undeclared (first use in this function)
  while(i<n)
        ^
/in/foo.c:7:8: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:10:12: error: 'tem' undeclared (first use in this function)
      sn=sn+tem;
            ^~~
/in/foo.c:5:24: warning: unused variable 'sum' [-Wunused-variable]
     int a,n,sn=0,ten=0,sum=0;
                        ^~~