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:

Now, Here is an example to show that:

The ELSE keyword is optional. Example:

Another note, the ENDIF keyword is optional if there is only one instruction to execute:

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:

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.

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:

Do ... Loop

Sometimes we don't know the number of loops to do. But we know how it must stop. Here is an example:

We can also use the WHILE keyword instead of UNTIL to make a loop structure with a condition.

While

About WHILE, there is a loop structure specially for While:

You can go to the next tutorial, we have finished with loops.