title: c++ string to boost::multiprecision::cpp_int
body: <p>How would I convert a string to "boost::multiprecision::cpp_int"?</p>
  
  <p>Additionally, I have a .txt file with 100 numbers each of 50 digits and I use ifstream to read them line by line into a string array. How can I convert each string from the array into a <code>cpp_int</code>, then add all the 100 numbers and get the sum?</p>