# 6.4. Naming Input¶

What if we want to draw a different size square, like one with a side length of 50? We could change each of the calls to the `forward`

procedure as shown below.

But, this means we have to change each of the four `forward`

statements and we could make a mistake and not set all of them to the same number. Is there a better way? What if we create a variable `size`

and set its value to the amount to move forward?

- 100
- How much will it go forward?
- 50
- What value is size set to?
- 200
- Size is set to 200 in line 2 so this will draw a square that has a side length of 200.
- 90
- It turns 90 degrees. It doesn't go forward 90.

What is the side length for a square drawn by the following procedure?

```
def square(turtle):
size = 200
turtle.forward(size)
turtle.right(90)
turtle.forward(size)
turtle.right(90)
turtle.forward(size)
turtle.right(90)
turtle.forward(size)
turtle.right(90)
```

Now the program is easier to change since we only have one line to change `size = 50`

to draw another size square. But, we still have to change the program in order to draw a different size square. Is there a better way?

We can add an additional input to the function that specifies the size of the square. Just separate the names for the inputs with a comma: `(turtle,size)`

as shown below and be sure to specify the actual size when you call the procedure `square(malik, 100)`

or `square(malik, 50)`

.

- square
- Check the 2nd and 4th forwards. How much do they move forward by?
- rectangle
- This will draw a rectangle with two sides with the specified size and two sides half that size. Copy this code into the area above and run it.
- triangle
- A triangle has 3 sides.

What shape would the following code draw?

```
def mystery(turtle,size):
turtle.forward(size)
turtle.right(90)
turtle.forward(size / 2)
turtle.right(90)
turtle.forward(size)
turtle.right(90)
turtle.forward(size / 2)
turtle.right(90)
from turtle import * # use the turtle library
space = Screen() # create a turtle screen (space)
malik = Turtle() # create a turtle named malik
mystery(malik, 100) # draw something with size = 100
```

The inputs that are specified in a function or procedure definition are also called **parameters** or **formal parameters**. So `turtle`

and `size`

are both parameters (formal parameters) in the `square`

procedure. Notice that when we call `square`

we have to specify the actual values for the inputs. The actual values passed into the function as inputs are called the **arguments** or **actual parameters**. In the call `square(malik, 50)`

both `malik`

and `50`

are arguments (actual parameters) to the `square`

procedure.

- turtle and size
- These are the names of the parameters (formal parameters).
- malik and 25
- Look again at the code above. Is that the name of this turtle?
- imani and 25
- The turtle is named imani and the size is 25 in the code: square(imani, 25).

In the following code what are the arguments (actual parameters)?

```
def square(turtle,size):
turtle.forward(size)
turtle.right(90)
turtle.forward(size)
turtle.right(90)
turtle.forward(size)
turtle.right(90)
turtle.forward(size)
turtle.right(90)
from turtle import * # use the turtle library
space = Screen() # create a turtle screen (space)
imani = Turtle() # create a turtle named imani
square(imani, 25) # draw a square with size 25
```

The following code assumes that a procedure square has been defined that takes a size. The code should create a turtle and then use it to draw a square, move forward, and draw a second square as shown at left, <img src=”../_static/SquareForwardSquare.png” width=”150” align=”left” hspace=”10” vspace=”5”/> but the lines are mixed up. Drag the lines into the correct order on the right.