View Compilation Error

113173_0_3181.cpp: In function `int main()':
113173_0_3181.cpp:11: error: `a' undeclared (first use this function)
113173_0_3181.cpp:11: error: (Each undeclared identifier is reported only once for each function it appears in.)
113173_0_3181.cpp:20: error: `s' undeclared (first use this function)