Learn to Program with Small Basic

Introducing the For Loop
As you start writing longer programs, you’ll need to repeat some statements.
For example, let’s make the turtle draw a square: enter the code
shown in Listing 5-6.
1 ' Square1.sb
2 Turtle.Move(60) ' Moves 60 pixels
3 Turtle.TurnRight() ' Turns right 90 degrees
4 Turtle.Move(60) ' Moves 60 pixels
5 Turtle.TurnRight() ' Turns right 90 degrees
6 Turtle.Move(60) ' Moves 60 pixels
7 Turtle.TurnRight() ' Turns right 90 degrees
8 Turtle.Move(60) ' Moves 60 pixels
9 Turtle.TurnRight() ' Turns right 90 degrees
Listing 5-6: Making the turtle draw a square
The turtle starts facing upward. This code tells the turtle to move
60 pixels up to draw one side of the square, turn 90 degrees to the right,
move 60 pixels to draw another side, turn 90 degrees to face downward,
move 60 pixels to draw a third side, turn 90 degrees to face left, and move
60 pixels to complete the square. Finally, the turtle turns 90 degrees one
last time so it’s facing upward like it was at the beginning. Check out the
result in Figure 5-9. Does your screen look the same?
20
Start
Turtle.Move(60)
Turtle.TurnRight()
Turtle.Move(60)
Turtle.TurnRight()
Turtle.Move(60)
Turtle.TurnRight()
Turtle.Move(60)
Turtle.TurnRight()
Figure 5-9: Drawing a square using move and turn commands
You repeated the Move(60) and TurnRight() methods four times. The computer
doesn’t mind repeating these tasks, but it’s boring for you to type all
that code. Wouldn’t it be great if you could make the turtle draw this square
using an easier approach?
Well, you can! You can make the turtle draw the same square as in
Listing 5-6, just by using a few lines of code. Use a For loop, like the one
in Listing 5-7.
1 ' Square2.sb
2 For I = 1 To 4 ' Repeats 4 times
3 Turtle.Move(60) ' Draws one side
4 Turtle.TurnRight() ' Turns right 90 degrees
5 EndFor
Listing 5-7: Making the turtle draw a square using a For loop
62 Chapter 5