/in/foo.c: In function 'main':
/in/foo.c:7:2: error: variable-sized object may not be initialized
  int a[n][m]={0};
  ^~~
/in/foo.c:7:15: warning: excess elements in array initializer
  int a[n][m]={0};
               ^
/in/foo.c:7:15: note: (near initialization for 'a[0]')
/in/foo.c:7:2: warning: excess elements in array initializer
  int a[n][m]={0};
  ^~~
/in/foo.c:7:2: note: (near initialization for 'a')
/in/foo.c:5:6: warning: unused variable 'p' [-Wunused-variable]
  int p;
      ^