/in/foo.c: In function 'main':
/in/foo.c:7:16: error: 'n' undeclared (first use in this function)
  scanf("%d%d",&n,&m);
                ^
/in/foo.c:7:16: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:7:19: error: 'm' undeclared (first use in this function)
  scanf("%d%d",&n,&m);
                   ^