View Compilation Error

0_0_3003959_14144.cpp: In function `int main()':
0_0_3003959_14144.cpp:520: error: no match for 'operator=' in 'mx = string(72u, 57, ((const std::allocator<char>&)((const std::allocator<char>*)(&allocator<char>()))))'
0_0_3003959_14144.cpp:104: note: candidates are: void bigint::operator=(bigint)
0_0_3003959_14144.cpp:111: note:                 void bigint::operator=(int)
0_0_3003959_14144.cpp:120: note:                 void bigint::operator=(char*)