Chapter 7. Truth, Comparison and Conditional
Processing

Condition Exercises

Develop an “or-guard”. In the example above we showed the “and-guard”
pattern:

average = count != 0 and float(sum)/count

Develop a similar technique using or.

Compare this with the if-else
operator.

Come Out Win. Assume d1 and d2 have
the numbers on two dice. Assume this is the come out roll in Craps.
Write the expression for winning (7 or 11). Write the expression for
losing (2, 3 or 12). Write the expression for a point (4, 5, 6, 8, 9
or 10).

Field Win. Assume d1 and d2 have
the numbers on 2 dice. The field pays on 2, 3, 4, 9, 10, 11 or 12.
Actually there are two conditions: 2 and 12 pay at one set of odds
(2:1) and the other 5 numbers pay at even money. Write two two
conditions under which the field pays.

Hardways. Assume d1 and d2 have
the numbers on 2 dice. A hardways proposition is 4, 6, 8, or 10 with
both dice having the same value. It's the hard way to get the
number. A hard 4, for instance is d1+d2 == 4 and d1 ==
d2. An easy 4 is d1+d2 == 4 and d1 != d2.

You win a hardways bet if you get the number the hard way. You
lose if you get the number the easy way or you get a seven. Write the
winning and losing condition for one of the four hard ways
bets.

Sort Three Numbers. This is an exercise in constructing if-statements. Using only
simple variables and if statements, you should be able to get this
to work; a loop is not needed.

Given 3 numbers (X,
Y, Z), assign
variables x, y,
z so that x ≤
y ≤ z and x,
y, and z are from
X, Y, and
Z. Use only a series of if-statements and
assignment statements.

Hint. You must define the conditions under which you choose
between x←X,
x←Y or
x←Z. You will do a
similar analysis for assigning values to y and
z. Note that your analysis for setting
y will depend on the value set for
x; similarly, your analysis for setting
z will depend on values set for
x and y.

Come Out Roll. Accept d1 and d2 as
input. First, check to see that they are in the proper range for
dice. If not, print a message.

Otherwise, determine the outcome if this is the come out roll.
If the sum is 7 or 11, print winner. If the sum is 2, 3 or 12, print
loser. Otherwise print the point.

Field Roll. Accept d1 and d2 as
input. First, check to see that they are in the proper range for
dice. If not, print a message.

Otherwise, check for any field bet pay out. A roll of 2 or 12
pays 2:1, print "pays 2"; 3, 4, 9, 10 and 11 pays 1:1, print "pays
even"; everything else loses, print "loses"

Harways Roll. Accept d1 and d2 as
input. First, check to see that they are in the proper range for
dice. If not, print a message.

Otherwise, check for a hard ways bet pay out. Hard 4 and 10 pays
7:1; Hard 6 and 8 pay 9:1, easy 4, 6, 8 or 10, or any 7 loses.
Everything else, the bet still stands.

Partial Evaluation. This partial evaluation of the and and
or operators appears to violate the
evaluate-apply principle espoused in The Evaluate-Apply Cycle. Instead of evaluating all
parameters, these operators seem to evaluate only the left-hand
parameter before they are applied. Is this special case a problem?
Can these operators be removed from the language, and replaced with
the simple if-statement? What are the
consequences of removing the short-circuit logic operators?

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