View Compilation Error

0_0_12853127_2575.cpp: In function `int main()':
0_0_12853127_2575.cpp:22: error: `a' undeclared (first use this function)
0_0_12853127_2575.cpp:22: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_12853127_2575.cpp:22: error: expected `;' before '}' token