In the switch statement your testing ints, not chars so don't use '. Your statement should look like: case 1: cout << "You entered roman numeral I";
Another thing you have usingnamespace. Using namespace what? You should add std after it so it looks like: usingnamespace std;
Two other things to mention using System ("pause"); is bad practice and next time please use code tags, they are the <> button on the right side of the submission box.