/in/foo.c: In function 'main':
/in/foo.c:13:3: error: 'k' undeclared (first use in this function)
   k=k*10;
   ^
/in/foo.c:13:3: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:5:18: warning: unused variable 'm' [-Wunused-variable]
  int a,n,sum,b,c,m;
                  ^