View Compilation Error

300226_0_1842.cpp: In function `int main()':
300226_0_1842.cpp:13: error: `xo' undeclared (first use this function)
300226_0_1842.cpp:13: error: (Each undeclared identifier is reported only once for each function it appears in.)
300226_0_1842.cpp:13: error: `yo' undeclared (first use this function)