/in/foo.cc: In function 'int main()':
/in/foo.cc:12:15: error: expected ']' before ')' token
    s[a[i]+a[j])=1;
               ^
/in/foo.cc:12:15: error: expected ';' before ')' token
/in/foo.cc:12:15: warning: statement has no effect [-Wunused-value]
    s[a[i]+a[j])=1;
    ~~~~~~~~~~~^