Although the CLR allows it, C# does not allow structs to have a default parameterless constructor. The reason is that, for a value type, compilers by default neither generate a default constructor, nor do they generate a call to the default constructor. So, even if you happened to define a default constructor, it will not be called and that will only confuse you. To avoid such problems, the C# compiler disallows definition of a default constructor by the user. And because it doesn't generate a default constructor, you can't initialize fields when defining them.
For instance, an array of value types will be initialized to the initial values of its members—i.e., zero for number type primitive members, null for reference types, and so forth—and not to the values provided in a default constructor. This feature makes structs perform better; because, constructor code need not be called.
So, requiring that a constructor contain a minimum of one parameter reduces the possibility that a constructor will be defined which is expected to be called every time the struct type is built.
For more information about Struct: Please visit http://msdn.microsoft.com/en-us/library/ah19swz4(v=vs.71).aspx
