1. Structured programming
3 types of control structure
Sequential structure
Built into Python
Selection structure
The if statement
The if/else statement
The if/elif/else statement
Repetition structure
The while repetition structure
The for repetition structure
All have one entry point and one exit point

2. Sequence Control Structure
add grade to total
add 1 to counter
total = total + grade;
counter = counter + 1;
Fig. 3.1 Sequence structure flowchart with pseudo code.

3. if Selection Structure
print “Passed”
Grade >= 60
true
false
Fig. 3.3 if single-selection structure flowchart.

4. if/else Structure false true Grade >= 60 print “Passed”
print “Failed”
false
true
Fig. 3.4 if/else double-selection structure flowchart.

5. if/elif/else Selection Structure
condition a
true
false .
condition z
default action(s)
condition b
case a action(s)
case b action(s)
case z action(s)
if statement
first elif statement
last elif statement
else statement
Fig. 3.5 if/elif/else multiple-selection structure.

6. while Repetition Structure
Repetition Structures
Allow a program to repeat an action while a condition is true
Using while Repetition
Action(s) contained within the body of the loop
Condition should evaluate to false at some point
Otherwise infinite loop and program hangs

7. while Repetition Structure
true
false
Product = 2 * product
Product <= 1000
Fig. 3.8 while repetition structure flowchart.

8. Greatest common divisor algorithm
Get two integers a, b > 0 from the user
If a and b are the same, GCD = a, exit
Otherwise, repeat:
If a > b: Replace a with a % b. If a is now 0, GCD = b, exit.
Case b > a analogous

9. gcd.py
Note
% operator for table
if/else
indentation: dangling else

10. Running the program Input first integer > 0: 81
Input second integer > 0: 45
a b
The greatest common divisor of 81 and 45 is 9

11. for Repetition Structure
The for loop
Function range is used to create a list of values
range ( integer )
Values go from 0 up to given integer (i.e., not including)
range ( integer, integer )
Values go from first up to second integer
range ( integer, integer, integer )
Values go from first up to second integer but increases in intervals of the third integer
This loop will execute howmany times:
for counter in range ( howmany ):
and counter will have values
0, 1,.. howmany-1

12. Makes the counter go from zero to nine
1 # Fig. 3.18: fig03_18.py
2 # Counter-controlled repetition with the
3 # for structure and range function. 4
5 for counter in range( 10 ):
print counter
Fig03_18.py Program Output
Makes the counter go from zero to nine

13. range function Fig. 3.19 Function range.
Python 2.2b2 (#26, Nov , 11:44:11) [MSC 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> range( 10 )
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
Fig Function range.
Python 2.2b2 (#26, Nov , 11:44:11) [MSC 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> range( 10, 0, -1 )
[10, 9, 8, 7, 6, 5, 4, 3, 2, 1]
Fig Function range with a third value.

14. Another example Fig03_22.py Program Output
1 # Fig. 3.22: fig03_22.py
2 # Summation with for. 3
4 sum = 0 5
6 for number in range( 2, 101, 2 ):
sum += number 8
9 print "Sum is", sum
Loops from 2 to 101 in increments of 2
A sum of all the even numbers from 2 to 100
Sum is 2550

15. 3.15 break and continue Statements
The break statement
Used to make a loop stop looping
The loop is exited and no more loop code is executed
The continue statement
Used to continue the looping process
All following actions in the loop body are not executed
But the loop will continue to run

16. When x equals 5 the loop breaks. Only up to 4 will be displayed
1 # Fig. 3.24: fig03_24.py
2 # Using the break statement in a for structure. 3
4 for x in range( 1, 11 ): 5
if x == 5:
break 8
print x, 10
11 print "\nBroke out of loop at x =", x
The loop will go from 1 to 10
Fig03_24.py Program Output
When x equals 5 the loop breaks. Only up to 4 will be displayed
Shows that the counter does not get to 10 like it normally would have
Broke out of loop at x = 5

17. continue skips rest of body but continues loop
Fig03_26.py Program Output
1 # Fig. 3.26: fig03_26.py
2 # Using the continue statement in a for/in structure. 3
4 for x in range( 1, 11 ): 5
if x == 5:
continue 8
print x, 10
11 print "\nUsed continue to skip printing the value 5"
The loop will continue if the value equals 5
The value 5 will never be output but all the others will
Used continue to skip printing the value 5

18. Calling/invoking a function Details
Functions
Purpose
Building blocks for the program (separate functionality in independant parts)
Avoid code repetition
Calling/invoking a function
functionName ( argument1, argument2 )
Details
Variables created in a function are local to that function
Arguments are also local variables
A function may return a result using the return statement

19. Modules
A module contains useful function definitions and other elements
All of which are related in some way
The import keyword is used to include a module
A function from a module is invoked like this:
moduleName.functionName( arguments )

20. Functions in math Module
2.3 (#1, Aug , 10:37:16)
[GCC 3.1.1] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>>
>>> print sqrt( 900 )
Traceback (most recent call last):
File "<stdin>", line 1, in ?
NameError: name 'sqrt' is not defined
>>> import math
>>> print math.sqrt( 900 )
30.0
Fig. 4.2 Function sqrt of module math.

21. User-defined functions
Functions must be defined before they are used:
def functionName ( paramList ):
paramList is a comma separated list of parameters
The actions of the function then follow
They should all be indented appropriately
The actions are also called the block or the function body

22. The function returns the passed value multiplied by itself
1 # Fig. 4.4: fig04_04.py
2 # Creating and using a programmer-defined function. 3
4 # function definition
5 def square( y ):
return y * y 7
8 for x in range( 1, 11 ):
print square( x ), 10
11 print
Fig04_04.py Program Output
This is a function definition, the function is called square and is passed the value y
The function returns the passed value multiplied by itself
This calls the square function and passes it the value x

23. This is a function that receives three values Fig04_05.py
1 # Fig. 4.5: fig04_05.py
2 # Finding the maximum of three integers. 3
4 def maximumValue( x, y, z ):
maximum = x 6
if y > maximum:
maximum = y 9
if z > maximum:
maximum = z 12
return maximum 14
15 a = int( raw_input( "Enter first integer: " ) )
16 b = int( raw_input( "Enter second integer: " ) )
17 c = int( raw_input( "Enter third integer: " ) ) 18
19 # function call
20 print "Maximum integer is:", maximumValue( a, b, c )
21 print # print new line 22
23 d = float( raw_input( "Enter first float: " ) )
24 e = float( raw_input( "Enter second float: " ) )
25 f = float( raw_input( "Enter third float: " ) )
26 print "Maximum float is: ", maximumValue( d, e, f )
27 print 28
29 g = raw_input( "Enter first string: " )
30 h = raw_input( "Enter second string: " )
31 i = raw_input( "Enter third string: " )
32 print "Maximum string is: ", maximumValue( g, h, i )
This is a function that receives three values
Fig04_05.py
The function determines the greater of three values and returns it
Gets three integers, passes them to the maximumValue function, and displays the results to the user
The same process is performed on float and string variables to show the diversity of the function
Note: only possible because of dynamic typing! Function parameters not type declared

24. Fig04_05.py Program Output Enter first integer: 27
Enter first integer: 27
Enter second integer: 12
Enter third integer: 36
Maximum integer is: 36
Enter first float: 12.3
Enter second float: 45.6
Enter third float: 9.03
Maximum float is: 45.6
Enter first string: hello
Enter second string: programming
Enter third string: goodbye
Maximum string is: programming
Fig04_05.py Program Output