Loops in Python

Presented by
A.Arockia Abins
Department of CSE

Two modes
1.Interactive Mode
2.Script Mode
Interactive Mode
It is a command line which gives immediate result for
each statement.
Ex:
Script Mode
A script mode can store code in a file and it uses the
interpreter to execute the contents of file.
Ex:

Solving a problem
Input
Process
Output
Ex: Addition of two numbers
Input: x=10 y=5
Process: z = x + y
Output: z=15

Input / Output statements:
Input
input() function is used to get the input from the
user.
Ex:
Output
print() function is used to display the result to the
user.
Ex:

Input / Output statements:
Ex: addition of two numbers
x=int(input("Enter 1st no:"))
y=int(input("Enter 2nd no:"))
z=x+y;
print("Sum is ",z)

Q:write a program to find area of circle
Program:
r=float(input("Enter a radius:"))
a=3.14*r*r
print("Area of circle is ",a)

Q:Write a program to convert
Celsius to Fahrenheit
Program:
c=float(input("Enter a celsius value:"))
f=1.8*c+32
print("Fahrenheit value is: ",f)

Solve the following:
•Find the Error:
1)>>>1+’2’+3+’4’
2)>>>’15’*’95’
•Find the Output:
1)>>>4*’2’
2)>>>x=“hello,”
>>>x+=“world!”
>>>print(x)

Control flow statements
Decision Control
Statements
Sequence
control
statements
Selection
control
statements
Iterative control
statements

Sequence control statements
• In this case program is executed
sequentially from the first line to last line.
Example:
//addition of two numbers
z=x+y;
print("Sum is ",z)

Selection control statements
• Execute only a selected set of statements
Example:
//find the greatest of two numbers
if x>y:
print(x, "is greatest number") //Note:Indentation
else:
print(y, "is greatest number")

Q:write a program to find whether the given
number is even or odd.
Program:
x=int(input("Enter a no:"))
if x%2==0:
print(x, "is even number")
else:
print(x, "is odd number")

Q:write a program to find the greatest number
from three numbers.
Program:
z=int(input("Enter 3rd no:"))
if x>y:
if x>z:
print(x, "is a greatest number")
else:
if y>z:
print(y, "is a greatest number")
else:
print(z, "is a greatest number")

Iterative control statements
or
Loop Structures
• Iterative statements are decision control
statements that are used to repeat the
execution of a list of statements.
• Two types:
• while loop
• for loop

while Loop
-execute one or more statements while a particular
condition is True.
Syntax
.
while(condition): .
Body of the loop
Key points:
• Initialization
• Condition
• Increment / decrement
Body of The loop
condition
False
True

while loop
Example:
//Program to print first 10 numbers using
a while loop
i=0
while(i<=10):
print(i)
i=i+1

while loop
Example:
//Program to print first 10 numbers using
a while loop
i=0 //Initialization
while(i<=10): //Condition
print(i)
i=i+1 //Increment

Q:write a program to find the sum of N natural
numbers.
Input:5
Process:1+2+3+4+5
Output:15

numbers.
Program:
x=int(input("Enter a number:"))
i=0
s=0
while(i<=x):
s=s+i;
i=i+1
print("Sum is ",s)

Q:write a program to find the factorial of a given
number.
Input:5
Process:1*2*3*4*5
Output:120

number.
x=int(input("Enter a number:"))
i=1
f=1
while(i<=x):
f=f*i;
i=i+1
print("Factorial is ",f)

for loop
Syntax:
for variable in sequence:
statements block
Variable – used to store a value
Sequence – string , collection of integers or
range()

for loop
Example:
for i in 1,2,3,4,5:
print(i)

range() function
• It is a built-in function in python
that is used to iterate over a
sequence of numbers.
• Syntax:
• range(beg, end, step)

range() function
• Syntax:
• range(beg, end, step)
• Example:
• for i in range(1,11):
• print(i,end=" ")

Print of N natural numbers
while
•i=0
•while(i<6):
• print(i)
• i=i+1
for
•for i in range(6):
• print(i)

numbers.
Program:
s=0
for i in range(1,11):
s=s+i
print("Sum is",s)

number.
f=1
f=f*i
print("Factorial is",f)

Q:write a program to print the multiplication
table of n, where n is entered by user.
Input:
Enter any number:5
Output:
1 * 5 = 5
2 * 5 = 10
3 * 5 = 15
…
10 * 5 = 50

Q:write a program to print the multiplication
table of n, where n is entered by user.
n=int(input("Enter any number:"))
print("Multiplication table of", n)
print("*********************")
print(i,"*",n,"=",i*n)

Looping through an iterable:
for i in "welcome":
print(i);
names=["abc","def","ghi"]
for i in names:
print(i);
numbers=[10,25,7,46,73,16,49]
for i in numbers:
print(i);

Programming Problems
1) Write a program that prints numbers from 20 to 1.
2) Write a program to print the sum of all odd numbers from 1
to 100.
3) Write a program to generate Fibonacci series of N terms.

Loops in Python

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