Test control and loop structures
Without these structures, our programs would work in a sequential way, and would be very poor.
Test structures
This allows us to perform some instructions if a condition is true.
If ... Then
This is the structure the most basic:
condition is the expression to test. The condition signs are:
-
> : purely upper
-
< : purely lower
-
>= : upper or equal
-
<= : lower or equal
-
= : equal
-
<> : unlike
Thus we can compare two values, two variables for example:
If Variable1 = Variable2 Then
Here, the "=" sign indicates an equality test, and not a value being assigned to a variable (like in a = 1).
Now, Here is an example to show that:
Public Sub Main()
Dim age As Integer
Print "How old are you? "
Input age
If age >= 18 Then
Print "You are major."
Else
Print "You are minor."
Endif
End
The
ELSE keyword is optional. Example:
' Gambas module file
Public Sub Main()
Dim power As Integer = 15 'power in ch
If puissance < 15 Then
Print "Do you want to change your car? :p "
Endif
End
Another note, the
ENDIF keyword is optional if there is only one instruction to execute:
Public Sub Main()
Dim power As Integer = 15 'power in ch
If puissance < 15 Then Print "Do you want to change your car? :p "
End
The Select ... Case structure
We're using this structure when there are many values to test. With this structure, our code is more clear to read:
Public Sub Main()
Dim pays As string
Print "De quel pays venez-vous ?"
Input pays
pays= lcase(pays) 'remove uppercase
Select Case pays
Case "france"
Print "Bonjour !"
Case "england"
Print "Hello!"
Case "espana"
Print "Ola!"
Case "portugal"
Print "Hola !"
Case Else
print"??"
End Select
End
Loops
Loops allows you to repeat one or more instructions. Three loops type exists allowing you to do the same thing in a different way.
For
The For loop allows to repeat an instructions block
n times.
Public Sub Main()
Dim i As Integer
For i = 1 To 5
Print "Value of i: " & i
Next
End
When Gambas enters the loop for the first time, it applies the value 1 to
i, then executes next instructions until it meets the
NEXT keyword. Gambas returns to the beginning of loop, then increments the
i variable until it reaches 5. The loop instructions will be read 5 times:
Value of i: 1
Value of i: 2
Value of i: 3
Value of i: 4
Value of i: 5
Do ... Loop
Sometimes we don't know the number of loops to do. But we know how it must stop. Here is an example:
Public Sub Main()
Dim result As integer
Print "How many two and two?"
Do
Input result
Loop Until result = 4
PRINT "Congratulation! You have found :-) "
End
We can also use the
WHILE keyword instead of
UNTIL to make a loop structure with a condition.
Do
Input result
Loop While result <> 4
While
About
WHILE, there is a loop structure specially for While:
' Gambas module file
Public sub Main()
Dim age As Integer
While age < 10
Inc age
Print "Value of age : " & age
Wend
End
Value of age : 1
Value of age : 2
Value of age : 3
Value of age : 4
Value of age : 5
Value of age : 6
Value of age : 7
Value of age : 8
Value of age : 9
Value of age : 10
You can go to the next tutorial, we have finished with loops.