This document discusses different control structures in Python including sequential, selection, and repetition structures. Selection structures include the if, if/else, and if/elif/else statements which allow code to execute conditionally. Repetition structures like while and for loops allow code to repeat as long as a condition is true or for a set number of iterations. These control structures are basic building blocks that allow Python programs to execute code conditionally and iteratively.

1. Unit 2 Basic Python : Control Statements

2. control structures
• 3 control structures
• 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

3. 3
Sequence Control Structure
Fig. 3.1 Sequence structure flowchart with pseudo code.
add grade to
total
add 1 to counter
total = total + grade;
counter = counter + 1;

4. 4
if Selection Structure
Fig. 3.3 if single-selection structure
flowchart.
print “Passed”Grade >= 60
true
false

5. 5
if/else Structure
Fig. 3.4 if/else double-selection structure flowchart.
Grade >= 60
print “Passed”print “Failed”
false true

6. 6
if/elif/else Selection Structure
condition a
true
false
.
.
.
false
false
condition z
default action(s)
true
true
condition b
case a action(s)
case b action(s)
case z action(s)
if statement
first elif
statement
last
elif
statemen
t else
stateme
nt
Fig. 3.5 if/elif/else multiple-selection structure.

7. 7
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

8. 8
while Repetition Structure
true
false
Product = 2 *
product
Product <= 1000
Fig. 3.8 while repetition structure flowchart.