View Compilation Error

806022_0_0_19905.cpp: In function `int main()':
806022_0_0_19905.cpp:15: error: `a' undeclared (first use this function)
806022_0_0_19905.cpp:15: error: (Each undeclared identifier is reported only once for each function it appears in.)
806022_0_0_19905.cpp:15: error: `b' undeclared (first use this function)