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Note that the = sign in the statement userAge = 0 has a different meaning from the = sign we learned in Math. In programming, the = sign is known as an assignment sign. It means we are assigning the value on the right side of the = sign to the variable on the left. A good way to understand the statement userAge = 0 is to think of it as userAge <- 0.

The statements x = y and y = x have very different meanings in programming.

Confused? An example will likely clear this up.

Type the following code into your IDLE editor and save it.

x = 5

y = 10

x = y

print ("x = ", x)

print ("y = ", y)

Now run the program. You should get this output:

x = 10

y = 10

Although x has an initial value of 5 (declared on the first line), the third line x = y assigns the value of y to x (x <- y), hence changing the value of x to 10 while the value of y remains unchanged.

Next, modify the program by changing ONLY ONE statement: Change the third line from x = y to y = x. Mathematically, x = y and y = x mean the same thing. However, this is not so in programming.

Run the second program. You will now get

x = 5

y = 5

You can see that in this example, the x value remains as 5, but the value of y is changed to 5. This is because the statement y = x assigns the value of x to y (y <- x). y becomes 5 while x remains unchanged as 5.