[Tutor] first steps
sigurd at 12move.de
Thu Apr 1 19:41:26 EST 2004
On 28 Mar 2004, peter hodgson <- py at humnet.ucla.edu wrote:
> A. I DON'T UNDERSTAND THIS:
> Here is another example of variable usage:
> a = 1
> print a
> a = a + 1
> Even if it is the same variable on both sides [OF THE '='] the
> computer still reads it as: First find out the data to store [RIGHT
> SIDE OF THE '='?] and than [THEN] find out where the data goes [PRINT
The `=' sign is misleading; most people who have a feeling for
mathematics stumble first on this. Some languages use for assignment a
different sign to not confuse people.
You uses the right words. If you assign a value you have a left hand
side (lhs) and a right hand side (rhs). First the interpreter evaluates
the rhs and after that it assigns the returned value to the lhs.
So if you write
a = a + 1
the interprter first evaluates a+1, stores that value somewhere and
assigns then a to that value. From now on the old value of a is
> B. WHY WON'T THIS RUN?
> #while 1 == 1: would perpetuate the printing of "help..."
> #l3 - l6 [extracted from another program] should limit it to five times
> count = 0
> max_count = 5
> while count > max_count:
> count = count + 1
> print "help, i'm caught in a loop"
> #but the program won't run
A while loop runs as long as the test in its head returns True. Now
look at your test condition: what does it return?
> C.HAVE I PARSED THIS RIGHT?
> #values into/out of a pail; #this is l1
> a = 1 #this means a = non-zero, that it is;
> s = 0 #empty pail
> print "enter numbers to add to the sum" #plus or minus
> print "enter 0 to quit" #end the game
> while a != 0: #i.e., you're still playing the game;
> print "current sum:", s #so we start at 0
> a = input("nmber? ") #and we alter s by a, superceding a = 1
> s = s + a #and a is the increment
> #reducing s to 0 won't close program
> print "total sum = ", s #not indented cause it only runs at the end
> #l2, l3 provide the contents and the pail;
> #l5, l6 provide for a way to end the game;
IMO no. line 5 prints only a message to the screen. line 6 is the line
which holds the test condition.
> #playing the game is l4, plus the indented lines l7 - l9;
Maybe. I wouldn't know which line should not belong to the game (except
line 1 since it's only a comment). If you deleted any other line the
game wouldn't run the way it does now.
Please do *not* send copies of replies to me.
I read the list
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