Tp add to what Phil and Richard have said ...
In C#, all variables must explicitly be given a value before they are used: if there is any path through code between the declaration of a variable and iit's usage, the compiler will complain - even if that route is impossible to follow in the "real world".
C++ is not so ... accurate, and because it uses pointers which are deliberately much harder to use in C# it is possible to write code like this:
int x;
int *p = &x;
*p = 10;
int y = x;
The mechanics of what is going on means that it is impossible to get to the final line without assigning a value to x indirectly. C# doesn't allow that, so even if you could "translate" the C++ code directly to C# the compiler still wouldn't like it.
In C# you must explicitly give a variable a value before you use it.