/in/foo.c: In function 'main':
/in/foo.c:7:6: error: 'i' undeclared (first use in this function)
  for(i=1;i<=n;i++);
      ^
/in/foo.c:7:6: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:7:2: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
  for(i=1;i<=n;i++);
  ^~~
/in/foo.c:8:3: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the 'for'
   scanf("%d %d\n",&ai,&bi);
   ^~~~~