Code-2 Variables and =

This is a short section, to add the idea of variables to the code.

• A "variable" is like a box that holds a value
    x = 7;
• The above line stores the value 7 into the variable named x
• Later appearances of x in the code retrieve the value from the box
• Using = in this way is called "variable assignment"
• How we use variables in CS101:
  -Assign a value into a variable once
  -Then use that variable many times below

• Experiments:
  -Try assigning (=) these values to x: 8, "hi"
• The name x can be anything we choose, so long as we are consistent
  -Try changing it to xyz throughout
• The Point: store a value once, use it on several lines, can save repetition
• Not the same as = in algebra, that means two things are equal forever
• = in code is simple -- just puts a value in a box when that line runs

Variables work as a shorthand -- we use = to assign a value into a variable, and then use that variable on later lines to retrieve that value. In the simplest case, this just works to avoid repeating a value: we store the value once, and then can use it many times. All computer languages have some form of variable like this, storing and retrieving values.

You Try It

Change the code below so it produces the following output. Use a variable to store the string "Aardvark" in a variable on the first line like x = "Aardvark";, then use the variable x on the later lines. In this way, changing just the first line to use the value "Zebra" or "Alice" or whatever changes the output of the whole program. The print() function automatically puts spaces between multiple items.

Aardvark Aardvark Aardvark
Here is Aardvark
Aardvark has arrived

x = "Aardvark"
print(x, x, x);
print("Here is", x);
print(x, "has arrived");