foo.c: In function 'main':
foo.c:9:13: error: 'i' undeclared (first use in this function)
    9 |         for(i=0,i;i<n;i++)
      |             ^
foo.c:9:13: note: each undeclared identifier is reported only once for each function it appears in
foo.c:9:16: warning: left-hand operand of comma expression has no effect [-Wunused-value]
    9 |         for(i=0,i;i<n;i++)
      |                ^
foo.c:16:16: warning: left-hand operand of comma expression has no effect [-Wunused-value]
   16 |         for(i=0,i;i<n;i++)
      |                ^
foo.c:22:16: warning: left-hand operand of comma expression has no effect [-Wunused-value]
   22 |         for(i=0,i;i<n;i++)
      |                ^
foo.c:7:13: warning: variable 'b' set but not used [-Wunused-but-set-variable]
    7 |         int b[1000];
      |             ^
foo.c:6:13: warning: variable 'a' set but not used [-Wunused-but-set-variable]
    6 |         int a[1000];
      |             ^

[Hydro](https://hydro.ac)提供评测服务