# knerr cs21 notes...

back to schedule
```
WEEK03: booleans, logical operators, conditionals (if/else)
---------------------------------------------------------------
M: review quiz 1, booleans, if/else

LAB2: due Tuesday

FROM QUIZ 1...this is *not* and accumulator (result is always 5):

def main():
result = 5
for i in range(10):
print result * i

print "result = %d" % (result)
print "     i = %d" % (i)

main()

this one *is* an accumulator. what would it print??

def main():
result = 5
for i in range(4):
result = result + i
print result

print "result = %d" % (result)
print "     i = %d" % (i)

main()

can also accumulate strings, like this:

def main():
newtitle = "\n\n   "
for ch in title:
newtitle = newtitle + ch + "  "

newtitle = newtitle + "\n\n "
print newtitle

main()

BOOLEANS...a new type

>>> x = True
>>> type(x)
<type 'bool'>
>>> y = true
Traceback (most recent call last):
File < stdin > line 1, in < module >
NameError: name 'true' is not defined
>>> z = False
>>> type(z)
<type 'bool'>
>>> print z
False
>>>

COMPARISON OPERATORS (be careful with ==)

>>> i=10
>>> j=15
>>> i < j
True
>>> i > j
False
>>> i == j
False
>>> i >= j
False
>>> i != j
True
>>>

CONDITIONAL STATEMENTS:

if < condition >
do this
and this
else:
do that

--> can do if without an else

>>> if i < j:
...   print "i is less than j"
...
i is less than j

>>> if i == j:
...   print "i and j are equal"
... else:
...   print "i is not equal to j"
...
i is not equal to j
>>>

```