You should explicitly create class instances. In your case
// It's quite enough since Patient is a struct
Patient[] patientInfo = new Patient[10];
In case of Patientn
that is class it should be
// As it was...
Patientn[] patientInfo = new Patientn[10];
// You should add this since Patientn is a class
for (int i = 0; i < patientInfo.Length; ++i)
patientInfo[i] = new Patientn();