could anyone help me understand this code whow it functions especially line 23

[Malouda]

1 ' Fig. 7.5: StudentPoll.vb
2 ' Using arrays to display poll results.
3
4 Imports System.Windows.Forms
5
6 Module modStudentPoll
7
8 Sub Main()
9 Dim answer, rating As Integer
10 Dim output As String
11
12 ' student response array (typically input at run time)
13 Dim responses As Integer()
14 responses = New Integer() {1, 2, 6, 4, 8, 5, 9, 7, _
15 8, 10, 1, 6, 3, 8, 6, 10, 3, 8, 2, 7, 6, 5, 7, 6, _
16 8, 6, 7, 5, 6, 6, 5, 6, 7, 5, 6, 4, 8, 6, 8, 10}
17
18 ' response frequency array (indices 0 through 10)
19 Dim frequency As Integer() = New Integer(10) {}
20
21 ' count frequencies
22 For answer = 0 To responses.GetUpperBound(0)
23 frequency(responses(answer)) += 1
24 Next
25
26 output &= "Rating " & vbTab & "Frequency " & vbCrLf
27
28 For rating = 1 To frequency.GetUpperBound(0)
29 output &= rating & vbTab & frequency(rating) & vbCrLf
30 Next
31
32 MessageBox.Show(output, "Student Poll Program", _
33 MessageBoxButtons.OK, MessageBoxIcon.Information)
34 End Sub ' Main
35
36 End Module ' modStudentPoll
Fig. 7.5
 
 

[Rabbit]

What line 23 does is take the answer given in response and increments the freqency array at that index. So if the response is 2, then it adds one to frequency(2). Which means that the number at frequency(2) is the number of people that responded with an answer of 2.

[Malouda]

Thanks Rabbit but i still didn't get you well,line 23 says
frequency(response(answer))+=1 now when answer is 0 response(0)=1 then it becomes frequency(1)+=1 now is the 1 in the frequency(1)referencing an index?

[Rabbit]

It doesn't become frequency(1). frequency(0) would = 1 in your example. frequency(1) would still = 0 until someone answers 1.

response = (1,2,1)
response(0) = 1
response(1) = 2
response(2) = 1
 
frequency(0) = 0
frequency(1) = 0
frequency(2) = 0
 
frequency(response(0)) += 1
frequency(1) += 1
frequency(1) = 1
 
frequency(response(1)) += 1
frequency(2) += 1
frequency(2) = 1
 
frequency(response(2)) += 1
frequency(1) += 1
frequency(1) = 2

[Crusader2010]

That code computes how many times a certain response was given. A response can be between 1 and 10. So,

frequency(1) = frequency of response 1 = how many times 1 appears in responses.
frequency(7) = frequency of response 7 = how many times 7 appears in responses.

Now, since you have an array of responses, from 0 to responses.getupperbound(0), you cycle through this array and you increment the value of the corresponding frequency of the response when found. In other words, if response(i) = 8, you have frequency(8) +=1. Which is what line 23 is doing, frequency(response(i))+=1. In your code 'i' = 'answer' as the iterator in the loop.

Also, x += y means x = x+y