View Compilation Error

0_0_6454920_5533.cpp: In function `int main()':
0_0_6454920_5533.cpp:15: error: `a' undeclared (first use this function)
0_0_6454920_5533.cpp:15: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_6454920_5533.cpp:17: error: `b' undeclared (first use this function)