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# Iteration/Control Statements - Python

state · while · for · break · continue · pass

ITERATION/CONTROL STATEMENTS:

·                 state

·                 while

·                 for

·                 break

·                 continue

·                 pass

## State:

Transition from one process to another process under specified condition with in a time is called state.

## While loop:

·                 While loop statement in Python is used to repeatedly executes set of statement as long as a given condition is true.

·                 In while loop, test expression is checked first. The body of the loop is entered only if the test_expression is True. After one iteration, the test expression is checked again. This process continues until the test_expression evaluates to False.

·                 In Python, the body of the while loop is determined through indentation.

·                 The statements inside the while starts with indentation and the first unindented line marks the end.

### Examples:

1.              program to find sum of n numbers:

2.              program to find factorial of a number

3.              program to find sum of digits of a number:

4.              Program to Reverse the given number:

5.              Program to find number is Armstrong number or not

6.              Program to check the number is palindrome or not

### Sum of n numbers:

n=eval(input("enter n"))

i=1

sum=0

while(i<=n):

sum=sum+i

i=i+1

print(sum)

output

enter n

10

55

### Factorial of a numbers:

n=eval(input("enter n"))

i=1

fact=1

while(i<=n):

fact=fact*i

i=i+1

print(fact)

output

enter n

5

120

### Sum of digits of a number:

n=eval(input("enter a number"))

sum=0

while(n>0):

a=n%10

sum=sum+a

n=n//10

print(sum)

output

enter a number

123

6

### Reverse the given number:

n=eval(input("enter a number"))

sum=0

while(n>0):

a=n%10

sum=sum*10+a

n=n//10

print(sum)

enter a number

123

321

### Armstrong number or not

n=eval(input("enter a number"))

org=n

sum=0

while(n>0):

a=n%10

sum=sum+a*a*a

n=n//10

if(sum==org):

print("The given number is Armstrong number")

else:

print("The given number is not

Armstrong number")

output

enter a number153

The given number is Armstrong number

### Palindrome or not

n=eval(input("enter a number"))

org=n

sum=0

while(n>0):

a=n%10

sum=sum*10+a

n=n//10

if(sum==org):

print("The given no is palindrome")

else:

print("The given no is not palindrome")

output

enter a number121

The given no is palindrome

### for in range:

v                 We can generate a sequence of numbers using range() function. range(10) will generate numbers from 0 to 9 (10 numbers).

v                 In range function have to define the start, stop and step size as range(start,stop,step size). step size defaults to 1 if not provided.

Syntax

### For in sequence

The for loop in Python is used to iterate over a sequence . Iterating over a sequence is called traversal. Loop continues until we reach the last element in the sequence.

The body of for loop is separated from the rest of the code using indentation.

### Sequence can be a list, strings or tuples

Examples:

1.              print nos divisible by 5 not by 10:

2.              Program to print fibonacci series.

3.              Program to find factors of a given number

4.              check the given number is perfect number or not

5.              check the no is prime or not

6.              Print first n prime numbers

7.              Program to print prime numbers in range

### print nos divisible by 5 not by 10

n=eval(input("enter a"))

for i in range(1,n,1):

if(i%5==0 and i%10!=0):

print(i)

enter a:30

5

15

25

### Fibonacci series

a=0

b=1

n=eval(input("Enter the number of terms: "))

print("Fibonacci Series: ")

print(a,b)

for i in range(1,n,1):

c=a+b

print(c)

a=b

b=c

output

Enter the number of terms: 6

Fibonacci Series:

0 1

1

2

3

5

8

### find factors of a number

n=eval(input("enter a number:"))

for i in range(1,n+1,1):

if(n%i==0):

print(i)

Output

enter a number:10

1

2

5

10

### check the no is prime or not

n=eval(input("enter a number"))

for i in range(2,n):

if(n%i==0):

print("The num is not a prime")

break

else:

print("The num is a prime number.")

### output

enter a no:7

The num is a prime number.

### check a number is perfect number or not

n=eval(input("enter a number:"))

sum=0

for i in range(1,n,1):

if(n%i==0):

sum=sum+i

if(sum==n):

print("the number is perfect number")

else:

print("the number is not perfect number")

### Output

enter a number:6

the number is perfect number

### Program to print first n prime numbers

number=int(input("enter   no   of   prime

numbers to be displayed:"))

count=1

n=2

while(count<=number):

for i in range(2,n):

if(n%i==0):

break

else:

print(n)

count=count+1

n=n+1

### Output

enter  no  of  prime  numbers  to  be

displayed:5

2

3

5

7

11

### Program to print prime numbers in range

lower=eval(input("enter a lower range"))

upper=eval(input("enter a upper range"))

for n in range(lower,upper + 1):

if n > 1:

for i in range(2,n):

if (n % i) == 0:

break

else:

print(n)

output:

enter a lower range50

enter a upper range100

53

59

61

67

71

73

79

83

89

97

## BREAK

v       Break statements can alter the flow of a loop.

v       It terminates the current

v       loop and executes the remaining statement outside the loop.

v       If the loop has else statement, that will also gets terminated and come out of the loop completely.

Break

### example

for i in "welcome":

if(i=="c"):

break

print(i)

w

e

l

## CONTINUE

It terminates the current iteration and transfer the control to the next iteration in the loop.

Continue

### Example:

for i in "welcome":

if(i=="c"):

continue

print(i)

w

e

l

o

m

e

## PASS

v       It is used when a statement is required syntactically but you don’t want any code to execute.

v       It is a null statement, nothing happens when it is executed.

pass

break

### Example

for i in “welcome”:

if (i == “c”):

pass

print(i)

w

e

l

c

o

m

e

## else in for loop:

v       If else statement is used in for loop, the else statement is executed when the loop has reached the limit.

v       The statements inside for loop and statements inside else will also execute.

### example

for i in range(1,6):

print(i)

else:

print("the number greater than 6")

### output

1

2

3

4

5        the number greater than 6

## else in while loop:

v       If else statement is used within while loop , the else part will be executed when the condition become false.

v       The statements inside for loop and statements inside else will also execute.

### Program

i=1

while(i<=5):

print(i)

i=i+1

else:

print("the number greater than 5")

### output

1

2

3

4

5

the number greater than 5

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Problem Solving and Python Programming : Control Flow, Functions : Iteration/Control Statements - Python |