View Compilation Error

In file included from GCC4.9.2/x86_64-w64-mingw32/include/c++/cassert:43:0,
                 from 0_0_33325467_20420.cpp:2:
0_0_33325467_20420.cpp: In function 'int main()':
0_0_33325467_20420.cpp:10:28: error: 'lunghezza' was not declared in this scope
         assert(s.size() == lunghezza);
                            ^