/in/foo.cc: In function 'int main()':
/in/foo.cc:19:15: warning: pointer to a function used in arithmetic [-Wpointer-arith]
    if(s(i)+s[j]+s[i+j]==n-4)
               ^
/in/foo.cc:19:15: warning: pointer to a function used in arithmetic [-Wpointer-arith]
/in/foo.cc:19:22: warning: pointer to a function used in arithmetic [-Wpointer-arith]
    if(s(i)+s[j]+s[i+j]==n-4)
                      ^
/in/foo.cc:19:16: error: invalid operands of types 'int (*)(int)' and 'int(int)' to binary 'operator+'
    if(s(i)+s[j]+s[i+j]==n-4)
       ~~~~~~~~~^~~~~~~