Difference between declaration

Question

What is the difference between these two codes :

public uint? a;
public uint a;

I want to know what is the difference if we use ? after int or double or the others

Thanks in advance

Answer 1

uint? is a nullable type, it can hold null value, for example.

uint? a;
uint b;

a = null;
b = null; //this will cause error

in C# 4.0 you can check using null coalescing operator

    b = a ?? 0;

its same as

    if (a.HasValue)
        b = a;
    else
        b = 0;