/in/foo.cc: In member function 'int* Bigint::Calculate()':
/in/foo.cc:14:8: warning: address of local variable 'a' returned [-Wreturn-local-addr]
    int a[10000];
        ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:42:3: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
   for (i=0;a[i]>=0;i++);
   ^~~
/in/foo.cc:44:4: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the 'for'
    i--;
    ^
/in/foo.cc:45:9: warning: statement has no effect [-Wunused-value]
   for (i;i>=0;i--)
         ^