Python Control Structures.pptx

M Vishnuvardhan
Control Structures
Control Structures are used to modify the flow of the program.
There are two types of control structures
» Branching statements
» Looping statements

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Branching statements – if
Syntax:
if condition:
statement1
statement2
:
statementn
Next statement
eg:
if a>b:
print(“a is big”)
NOTE all the statements which need to part of the if should be placed in same
indentation

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if else
The if-else statement provides an else block combined with the if statement
which is executed in the false case of the condition.
Syntax:
if condition:
#block of statements
else:
#another block of statements (else-block)
Eg:
num = int(input("enter the number?"))
if num%2 == 0:
print("Number is even...")
else:
print("Number is odd...")

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elif statement
The elif statement enables us to check multiple conditions and execute the
specific block of statements depending upon the true condition among them. We
can have any number of elif statements in our program depending upon our need.
Syntax:
if expression 1:
# block of statements
elif expression 2:
elif expression 3:
else:

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Nested if
Nested if statements mean an if statement inside another if statement.
Syntax:
if (condition1):
# Executes when condition1 is true
if (condition2):
# Executes when condition2 is true
# inner if Block is end here
# outer if Block is end here

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Shorthand if & if else
If you have only one statement to execute, you can put it on the same line as the
if statement.
Syntax: if condition: #true block
Eg: if a > b: print("a is greater than b")
If you have only one statement to execute, one for if, and one for else, you can
put it all on the same line
Syntax: #true block if condition else #false block
Eg: print("A is big ") if a > b else print("B is big")
Note: This technique is known as Ternary Operators, or Conditional
Expressions.

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Looping - while
With the while loop we can execute a set of statements as long as a condition is
true.
Syntax: while condition:
#body of the loop
Eg: i = 1
while i < 6:
print(i)
i += 1
Note: remember to increment i, or else the loop will continue
forever.

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While loop with else
With the else statement we can run a block of code once when the condition no
longer is true
Syntax: while condition:
#body of the loop
else:
#false block
Eg: i = 1
while i < 6:
print(i)
i += 1
else:
print("i is no longer less than 6")

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For loop
For loop can used in two ways.
» Using on a sequence
» Using range()
A for loop is used for iterating over a sequence
(i.e, either a list, a tuple, a dictionary, a set,
or a string).
Syntax: for x in sequence:
body of the loop

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For loop - sequence
Looping through a List
Eg: fruits = ["apple", "banana", "cherry"]
for x in fruits:
print(x)
Looping through a String
name=“ssbn”
for x in name:
print(x)

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For loop – range()
The range() function returns a sequence of numbers, starting from 0 by default,
and increments by 1 (by default), and ends at a specified number.
range (start, stop, step)
start is the starting value and is inclusive optional (default-0)
Stop is the end value and is exclusive and is mandatory
Step is incrementation from start to end optional (default -1)
Syntax: for var in range(start, stop, step):
#body of the loop
Eg: for x in range(0,6,1):
print(x)

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For loop – range()
» Step can be optional default is 1
for x in range(0, 6):
print(x) #prints 0,1,2,3,4,5
» Start can be optional default is 0
for x in range(6):
print(x) #prints 0,1,2,3,4,5
» Step can be other than 1
for x in range(0,6,3):
print(x) #prints 0,3

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For loop with else
else keyword in a for loop specifies a block of code to be executed when the loop
is finished:
Eg: for x in range(6):
print(x)
else:
print("Finally finished!")

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Nested loops
A nested loop is a loop inside a loop. The "inner loop" will be executed one time
for each iteration of the "outer loop":
Eg:
adj = ["red", "big", "tasty"]
fruits = ["apple", "banana", "cherry"]
for x in adj:
for y in fruits:
print(x, y)

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Jump statements - break
The break keyword is used to break out a for loop, or a while loop.
Syntax : break
Eg: i = 1
while i < 9:
print(i)
if i == 3:
break
i += 1
Eg:
i = 1
for i in range(6):
print(i)
if i == 3:
break
i += 1

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Jump statements - continue
The continue keyword is used to end the current iteration in a for
loop (or a while loop), and continues to the next iteration.
Syntax: continue
Eg: for i in range(1,11):
if i%2!=0:
continue
print(i)

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Jump statements - pass
The pass statement is used as a placeholder for future code. When
the pass statement is executed, nothing happens, but avoids getting
an error when empty code is not allowed. Empty code is not allowed
in loops, function definitions, class definitions, or in if
statements
Syntax: pass
Eg: if(a<b):
pass
else:
print("b<a")

Python Control Structures.pptx

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Python Control Structures.pptx