View Compilation Error

0_0_26317919_24751.cpp: In function 'int main()':
0_0_26317919_24751.cpp:91:27: error: cannot convert 'std::string {aka std::basic_string<char>}' to 'const char*' for argument '1' to 'size_t strlen(const char*)'
         int len=strlen(str);
                           ^