View Compilation Error

0_0_4883339_9448.cpp: In function `int main()':
0_0_4883339_9448.cpp:6: error: `x1' undeclared (first use this function)
0_0_4883339_9448.cpp:6: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_4883339_9448.cpp:6: error: `x2' undeclared (first use this function)
0_0_4883339_9448.cpp:6: error: `y1' undeclared (first use this function)
0_0_4883339_9448.cpp:6: error: `y2' undeclared (first use this function)