[Numeracy 476] Re: Monday Puzzle

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Ladnor Geissinger ladnor at email.unc.edu
Sun Aug 8 01:19:10 EDT 2010


It is true that some programming languages that were developed early
in the computer age unfortunately used " = " for the assignment
operator. Later language designers generally refrained from that usage
and most commonly used instead " := " for assignment. Notice that
assignment is a one-way, before and then after, kind of operation where
left and right are not being treated symmetrically: evaluate the right
hand expression AND THEN assign the resulting value as the new current
value of the variable on the left. I think for students in elementary
math classes it would be a good idea to refrain from using X =
ExpressionB for assignment, especially when ExpressionB has the variable
X in it. In case Y is not a variable appearing in ExpressionB, why not
simply say "let Y be a nickname for ExpressionB" or "let Y have the
value of ExpressionB" or use the shorthand " Y := ExpressionB " ?

Ladnor Geissinger

On 8/3/2010 1:20 PM, Chip Burkitt wrote:

> Good point. Several programming languages also use the equal sign as

> an assignment operator. This can also be confusing. For example, the

> statement

> x = x + 1

> means "add one to the current value of x and store the result in x."

> For algorithms, many prefer

> x ← x + 1

>

> Chip Burkitt

>

> On 8/3/2010 11:15 AM, Ladnor Geissinger wrote:

>> Oh please, don't ever write such an obviously incorrect equation for

>> your students, and don't let them write things like that! No wonder

>> they think math is confusing and makes no sense.

>> 30 - 3 =27 and 27 - 2 =25 are both correct of course, but 30 - 3 = 27

>> - 2 is clearly wrong.

>>

>> Given two numerical expressions expr1 and expr2, when we write the

>> shorthand sentence " expr1 = expr2 " we mean that if, or when, you

>> evaluate both expressions then the resulting numbers are in fact the

>> same.

>> ---------------------------------------------------------------------------------------------------------------------

>>

>> On 8/3/2010 10:28 AM, McIntosh, Tricia wrote:

>>> $30 - $3 = $27 - $2 = $25

>>>


--
Ladnor Geissinger, Emer. Prof. of Mathematics
Univ. of North Carolina, Chapel Hill, NC 27599 USA

ladnor at email.unc.edu