View Compilation Error

0_0_11006504_16044.cpp: In function `int main()':
0_0_11006504_16044.cpp:18: error: `s1' undeclared (first use this function)
0_0_11006504_16044.cpp:18: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_11006504_16044.cpp:23: error: `s2' undeclared (first use this function)