Flow control describes the order in which statements will be executed at runtime.
I. Conditional Statements
1) if
if condition : statement
or
if condition : statement-1 statement-2 statement-3
If condition is true then statements will be executed.
Eg:
1) name=input("Enter Name:")
2) if name=="durga" :
3) print("Hello Durga Good Morning")
4) print("How are you!!!")
5)
6) D:\Python_classes>py test.py
7) Enter Name:durga
8) Hello Durga Good Morning
9) How are you!!!
10)
11) D:\Python_classes>py test.py
12) Enter Name:Ravi
13) How are you!!! 2) if-else:
if condition : Action-1 else : Action-2
if condition is true then Action-1 will be executed otherwise Action-2 will be executed.
Eg:
1) name=input("Enter Name:")
2) if name=="durga" :
3) print("Hello Durga Good Morning")
4) else:
5) print("Hello Guest Good Moring")
6) print("How are you!!!")
7)
8) D:\Python_classes>py test.py
9) Enter Name:durga
10) Hello Durga Good Morning
11) How are you!!!
12)
13) D:\Python_classes>py test.py
14) Enter Name:Ravi
15) Hello Guest Good Moring
16) How are you!!!3) if-elif-else:
Syntax:
if condition1: Action-1 elif condition2: Action-2 elif condition3: Action-3 elif condition4: Action-4 ... else: Default Action
Based condition the corresponding action will be executed.
Eg:
1) brand=input("Enter Your Favourite Brand:")
2) if brand=="RC" :
3) print("It is childrens brand")
4) elif brand=="KF":
5) print("It is not that much kick")
6) elif brand=="FO":
7) print("Buy one get Free One")
8) else :
9) print("Other Brands are not recommended")
10)
11)
12) D:\Python_classes>py test.py
13) Enter Your Favourite Brand:RC
14) It is childrens brand
15)
16) D:\Python_classes>py test.py
17) Enter Your Favourite Brand:KF
18) It is not that much kick
19)
20) D:\Python_classes>py test.py
21) Enter Your Favourite Brand:KALYANI
22) Other Brands are not recommended II. Iterative Statements
If we want to execute a group of statements multiple times then we should go for Iterative statements.
Python supports 2 types of iterative statements.
- for loop
- while loop
1) for loop:
If we want to execute some action for every element present in some sequence(it may be string or collection)then we should go for for loop.
Syntax:
for x in sequence : body
where sequence can be string or any collection.
Body will be executed for every element present in the sequence.
Eg 1: To print characters present in the given string
1) s="Sunny Leone" 2) for x in s : 3) print(x) 4) 5) Output 6) S 7) u 8) n 9) n 10) y 11) 12) L 13) e 14) o 15) n 16) e
Eg 2: To print Hello 10 times
1) for x in range(10) :
2) print("Hello") Eg 3: To display numbers from 0 to 10
1) for x in range(11) : 2) print(x)
Eg 4: To display odd numbers from 0 to 20
1) for x in range(21) : 2) if (x%2!=0): 3) print(x)
2) while loop:
If we want to execute a group of statements iteratively until some condition false,then we should go for while loop.
Syntax:
while condition : body
Eg: To print numbers from 1 to 10 by using while loop
1) x=1 2) while x <=10: 3) print(x) 4) x=x+1
Eg: To display the sum of first n numbers
1) n=int(input("Enter number:"))
2) sum=0
3) i=1
4) while i<=n:
5) sum=sum+i
6) i=i+1
7) print("The sum of first",n,"numbers is :",sum) Infinite Loops:
1) i=0;
2) while True :
3) i=i+1;
4) print("Hello",i) Nested Loops:
Sometimes we can take a loop inside another loop,which are also known as nested loops.
Eg: Write a program to dispaly *'s in Right angled triangled form
1) *
2) * *
3) * * *
4) * * * *
5) * * * * *
6) * * * * * *
7) * * * * * * *
8)
9) n = int(input("Enter number of rows:"))
10) for i in range(1,n+1):
11) for j in range(1,i+1):
12) print("*",end=" ")
13) print() III. Transfer Statements
1) break:
We can use break statement inside loops to break loop execution based on some condition.
Eg:
1) for i in range(10):
2) if i==7:
3) print("processing is enough..plz break")
4) break
5) print(i)
6)
7) D:\Python_classes>py test.py
8) 0
9) 1
10) 2
11) 3
12) 4
13) 5
14) 6
15) processing is enough..plz break 2) continue:
We can use continue statement to skip current iteration and continue next iteration.
Eg 1: To print odd numbers in the range 0 to 9
1) for i in range(10): 2) if i%2==0: 3) continue 4) print(i) 5) 6) D:\Python_classes>py test.py 7) 1 8) 3 9) 5 10) 7 11) 9
loops with else block:
Inside loop execution,if break statement not executed ,then only else part will be executed.
else means loop without break
Eg:
1) cart=[10,20,30,40,50]
2) for item in cart:
3) if item>=500:
4) print("We cannot process this order")
5) break
6) print(item)
7) else:
8) print("Congrats ...all items processed successfully")
9)
10)Output
11) 10
12) 20
13) 30
14) 40
15) 50
16) Congrats ...all items processed successfully 3) pass statement:
pass is a keyword in Python.
In our programming syntactically if block is required which won't do anything then we can define that empty block with pass keyword.
pass
|- It is an empty statement |- It is null statement |- It won't do anything
Eg:
if True: SyntaxError: unexpected EOF while parsing
if True: pass ==>valid
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