/in/foo.c: In function 'main':
/in/foo.c:5:15: error: 'i' undeclared (first use in this function)
    5 |         int a[i][j]={0};
      |               ^
/in/foo.c:5:15: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:5:18: error: 'j' undeclared (first use in this function)
    5 |         int a[i][j]={0};
      |                  ^
/in/foo.c:5:13: warning: unused variable 'a' [-Wunused-variable]
    5 |         int a[i][j]={0};
      |             ^