View Compilation Error

0_0_5516515_6880.cpp: In function `int main()':
0_0_5516515_6880.cpp:22: error: no match for 'operator-' in 'std::basic_string<_CharT, _Traits, _Alloc>::substr(typename _Alloc::size_type, typename _Alloc::size_type) const [with _CharT = char, _Traits = std::char_traits<char>, _Alloc = std::allocator<char>](0u, -1u) - 1'
0_0_5516515_6880.cpp:25: error: `substr' undeclared (first use this function)
0_0_5516515_6880.cpp:25: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_5516515_6880.cpp:27: error: no match for 'operator==' in 's1 == 1'
0_0_5516515_6880.cpp:27: error: no match for 'operator==' in 's2 == 1'