C++Primer第五版：练习2.39 2.40

练习2.39 return type of ‘main’ should be ‘int’ instead of ‘Foo’ expected a ‘:’ ‘Foo’ followed by ‘int’ is illegal(did you forget a ‘:’?)

练习2.40

#include<iostream> struct Sales_data { std::string bookNo; unsigned units_sold = 0; double price = 0.0; double revenue = 0.0 };