View Compilation Error

0_0_9256628_18904.cpp: In function `int main()':
0_0_9256628_18904.cpp:19: error: `a' undeclared (first use this function)
0_0_9256628_18904.cpp:19: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_9256628_18904.cpp:19: error: `b' undeclared (first use this function)