With constructor:

Vector v1 = new Vector();
v1.X = 1;
v1.Y = 2;
v1.Z = 3;

Console.WriteLine("X = {0}, Y = {1}, Z = {2}",v1.X,v1.Y,v1.Z);
// Output X=1,Y=2,Z=3

Vector v1 = new Vector();
//v1.X is not assigned
v1.Y = 2;
v1.Z = 3;

Console.WriteLine("X = {0}, Y = {1}, Z = {2}",v1.X,v1.Y,v1.Z);
// Output X=0,Y=2,Z=3

Point point1 = new Point();
point1.x = 0.5;
point1.y = 0.6;

Point point2 = new Point(0.5, 0.6);

Without constructor:

Vector v1;
v1.Y = 2;
v1.Z = 3;

Console.WriteLine("X = {0}, Y = {1}, Z = {2}",v1.X,v1.Y,v1.Z);
//Output ERROR "Use of possibly unassigned field 'X'

Vector v1;
v1.X = 1;
v1.Y = 2;
v1.Z = 3;

Console.WriteLine("X = {0}, Y = {1}, Z = {2}",v1.X,v1.Y,v1.Z);
// Output X=1,Y=2,Z=3

Point point3;
point3.x = 0.5;
point3.y = 0.6;

If we use a struct with its constructor, we aren’t going to have problems with unassigned field (each unassigned field has null value).

Unlike classes, a struct doesn’t have to be constructed, i.e. there is no need to use the new keyword, unless you need to call one of the constructors. A struct does not require the new keyword because is a value-type and thus cannot be null.