View Compilation Error

246915_0_18630.cpp: In function `int main()':
246915_0_18630.cpp:17: error: `s1' undeclared (first use this function)
246915_0_18630.cpp:17: error: (Each undeclared identifier is reported only once for each function it appears in.)
246915_0_18630.cpp:17: error: `s2' undeclared (first use this function)