Structure

1. Accessing structure and its properties

struct studentMarks {
   var mark1 = 100
   var mark2 = 200
   var mark3 = 300
}
let marks = studentMarks()
print("Mark1 is \(marks.mark1)")
print("Mark2 is \(marks.mark2)")
print("Mark3 is \(marks.mark3)")

Result

Mark1 is 100
Mark2 is 200
Mark3 is 300

2. Accessing Structure, passing value, re-initialize

 struct MarksStruct {
   var mark: Int

   init(mark: Int) {
      self.mark = mark
   }
}
var aStruct = MarksStruct(mark: 98)
var bStruct = aStruct // aStruct and bStruct are two structs with the same value!
bStruct.mark = 97
print(aStruct.mark) // 98
print(bStruct.mark) // 97

3.

struct markStruct { 
   var mark1: Int
   var mark2: Int
   var mark3: Int

   init(mark1: Int, mark2: Int, mark3: Int) {
      self.mark1 = mark1
      self.mark2 = mark2
      self.mark3 = mark3
   }
}

var marks = markStruct(mark1: 98, mark2: 96, mark3:100)
print(marks.mark1)
print(marks.mark2)
print(marks.mark3)

4. 

struct markStruct { 
   var mark1: Int
   var mark2: Int
   var mark3: Int

   init(mark1: Int, mark2: Int, mark3: Int){
      self.mark1 = mark1
      self.mark2 = mark2
      self.mark3 = mark3
   }
}

var fail = markStruct(mark1: 34, mark2: 42, mark3: 13)

print(fail.mark1)
print(fail.mark2)
print(fail.mark3)