1. CMSC 120: Visualizing Information 3/25/08
Conditions
CMSC 120: Visualizing Information
3/25/08

2. Control Flow Gotos: jump to different part of program Loops:
GOTO LINE 12
Functions
Loops:
repetition
for-statements
while-statements
Conditionals

3. Repetition is a Key Concept
World Population in 10 years
Repeatedly compute values for successive years
Add increase in population to prior population ten times
for year in range(10):
population = population * (1 + growthRate)

4. Another Way… year = 0 while year < 10:
population = population * (1 + growthRate)
year = year + 1

5. While-Statement
while <a condition is true>:
<do something>
Condition is tested and if it is True, then the body of the loop is executed.
The condition is tested again and as long as it remains True, then the loop will continue to repeat.

6. Loop Statements for while Index variable: year
while year < 10:
p = p * (1 + gR)
year = year + 1
for year in range(10):
p = p * (1 + gR)
Index variable: year
Initial value, step size, and stop value determined in for-statement
Always runs 10 times
Index variable: year
Initial value, step size, and stop value determined on different lines
Does not have to run 10 times

7. Fixed Number of Repetitions
# do something N times
for step in range(N):
do something...

8. Limited Duratoin # do something for some duration
while <waiting for condition>:
do something...
value = <initialState>
while value < finalState:

9. Forever
# do something forever
while True:
do something...

10. Conditions Booleans: True, False
In Python: False, None, 0, 0.0, and empty strings and lists are interpreted as false.
All other values are true.
Special Operators: logical and relational

11. Relational Operators < less than <= less than or equal to
> greater than
>= greater than or equal to
== equal to
!= not equal to
42 < 33
12 <= 23
42 > 33
12 >= 33
42 == 33
42 != 33

12. Relational Operators
>>> a, b, c = 10, 20, 10 >>> a == b >>> a == c >>> a == a >>> True == 1 >>> False == 1

13. Relational Operators
>>> ‘Hello’ == ‘Good Bye’ False >>> ‘Elmore’ < ‘Elvis’ True >>> ‘a’ < ‘A’

14. Relational Operators
And Or
Not