Section 5.0

You have already used these functions: InputBox, CStr, CInt, CDbl

The general form of a function call is:

   someVariable  =  functionName(parameter1, parameter2,   etc....)

The parameters are inputs to the function, which produces a result. A function call is also an expression, so we must handle the result in some way - e.g. store it.

However, VB is not very uniform - there are differences in how we call functions. For example, for mathematical functions (sqrt, sin, cos etc) we precede the name by Math. (Math is the name of a collection of related functions)

x = Math.sin(y)

For functions which manipulate strings, the string comes before the function name.

s = myName.Substring(2,3)

n = myName.Length       'nb you have seen the 'dot' notation before

   Dim s as string
   dim n as integer
   dim j as integer
   dim x as double

   ' sqrt - square root - one parameter, numeric result
   i = Math.sqrt(9)                 ' i is 3
   i = Math.sqrt(4)+Math.sqrt(9)          ' i is 5

   ' below, the inner sqr() is evaluated first
   x = Math.sqrt( Math.sqrt(4)  )               

     

    'Substring - returns a substring from  a longer string
    '  - it has 2 parameters:
    '     the starting position to extract from.  (the first chracter is numbered 0 )
    '     the length of the extracted string
    'NB the string to be worked on precedes the Substring
    'Examples:
    dim s as string = "position"     'NB p is at 0, o is at 1, etc
    dim answer as string
    answer = s.Substring(2, 3)       ' answer becomes sit



    'Length of a string - how many chars it contains
    dim s1 as String = "Sheffield"
    n = s1.Length                 ' n is 9

    n = Math.sqrt( Math.sqrt(16)) +1

    n = Math.sqrt(   4    ) +1
    n =            2        +1
    n=          3

Section 5.1

List of common functions

'some vars for the examples:
Dim i,j as Integer
Dim s, s1 as String
Dim a,b as Double
a = 2.34
b = 5.67
y = Math.cos(a)        ' cosine - also sin, sqrt, tan
i = Math.Max(a, b)   ' max of 2 values  - also Min
i = Math.Round(a)    ' rounds to nearest int - i.e. Math.Round(3.4) is 3
a = Math.PI          ' not a function -  a constant  (a becomes 3.141...etc)


'random numbers - needs 2 steps:
'do this once, just under the 'Class Form1 ...' line
Private myRandom As Random = New Random() 
'then do   
i = myRandom.Next(1,11)   ' i is a random number from 1 to 10 inclusive
i = myRandom.Next(1,11)   ' and another one



'strings
s= "  hello there!    "
s1 = s.SubString(2,3)
i = s.Length
s = s1.ToLower()      'convert s1 to lower-case.    Also ToUpper
s = s1.Trim()         ' trim  (remove) spaces from each end of s1
If IsNumeric(TextBox1.Text) then ..etc   ' test if a string holds a number

'position of substring (if s="guitar", then i is 4.  i=-1 if not found)
i = s.IndexOf("a") Then ...
   
If s.StartsWith("www.") Then ...etc  'if s starts with "www."  Also EndsWith

'formatting results:
Dim d as double = 3.56789
   s = String.Format("{0:n3}", n)     ' nb curly brackets
   messageBox.show(d)    ' displays 3.568  - i.e rounds to 3dp

d = 3.567
j = math.Floor(x)   ' j is 3  - truncates - rounds down

Section 5.2

problems - using functions

Private Sub Button1_Click(etc...    )
dim n as Double
dim answer as Double
n = 23.4
answer = Math.sqrt(n)
MessageBox.Show("Result is " &  answer)
End Sub

Private Sub Button1_Click(etc...   )
MessageBox.Show(CStr( sqr(23.4)))           
End Sub

A square office space is advertised as 3000 sq metres. How long is a side? (Do it the long way, using variables.)

2. Ask the user to enter their name, thenm display the first and last letters of the name, in 2 text boxes. (Use substring).  

Section 5.3

Key Points