NCERT Solution Flow of Control in Python Class 11 Chapter 6

Flow of Control in Python Class 11

Summary of Chapter

The if statement is used for selection or decision making.

The looping constructs while and for allow sections of code to be executed repeatedly under some condition.

for statement iterates over a range of values or a sequence.

The statements within the body of for loop are executed till the range of values is exhausted.

The statements within the body of a while are executed over and over until the condition of the
 while is false.

If the condition of the while loop is initially false, the body is not executed even once.

The statements within the body of the while loop must ensure that the condition eventually becomes
false; otherwise, the loop will become an infinite loop, leading to a logical error in the program.

The break statement immediately exits a loop, skipping the rest of the loop’s body. Execution continues
with the statement immediately following the body of  the loop. 

When a continue statement is encountered, the control jumps to the beginning of the loop for the
next iteration.

A loop contained within another loop is called a nested loop.

Flow of Control in Python Class 11

EXERCISE

Q1. What is the difference between else and elif construct of if statement?

Ans. if..else statement allows us to write two alternative paths and the control condition determines which path gets executed. If the condition is incorrect/False then else statement will execute. The syntax for if..else statement is as follows.

if condition:
       statement(s)
else:
       statement(s)

Many a times there are situations that require multiple conditions to be checked and it may lead to many alternatives. In such cases we can make a chain of conditions using elif. Syntax of elif is shown below:

if condition : 
    statement
elif condition :
    statement
elif condition :
    statement
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else :
   statement

Q2. What is the purpose of range() function? Give one example.

Ans. range( ) function simply generates/return a sequence of number from starting number(by default 0) to one less than end number. This function is commonly used in for loop. for example

for i in range(3, 7):
          print(i)

OUTPUT :

3

4

5

6

Flow of Control in Python Class 11

Q3. Differentiate between break and continue statements using examples.

Ans. break statement is used for immediate termination of loop for example

for i in range(7):
     if i==3:
          break
     print(i)
print("Loop Terminate")

OUTPUT :

0
1
2
Loop Terminate

continue statement is used to skip the current iteration of the loop and pass the control to the next iteration. for example :

for i in range(7):
     if i==3:
          continue
     print(i)
print("Loop Terminate")

OUTPUT :

0
1
2
4
5
6
Loop Terminate

Q4. What is an infinite loop? Give one example.

Ans. A never ending loop is called infinite loop. for example the following loop will print ‘A’ infinite times

i=0
while(i<=0):
     print("A")

Flow of Control in Python Class 11

Q5. Find the output of the following program segments:

a) a = 110
    while a > 100:
         print(a)
         a -= 2

Ans.

110
108
106
104
102

b) for i in range(20, 30, 2):
         print(i)

Ans.

20
22
24
26
28

c) country = 'INDIA' 
    for i in country:
          print (i)

Ans.

I
N
D
I
A

d) i = 0; sum = 0
    while i < 9:
         if i % 4 == 0:
              sum = sum + i
         i = i + 2
     print (sum)

Ans. 12

e) for x in range(1,4):
         for y in range(2,5):
              if x * y > 10:
                   break
              print (x * y)

Ans.

2
3
4
4
6
8
6
9

f) var = 7
   while var > 0:
        print ('Current variable value: ', var)
        var = var -1
        if var == 3:
             break
        else:
             if var == 6:
                  var = var -1
                  continue
         print ("Good bye!")

Flow of Control in Python Class 11

PROGRAMMING EXERCISES

Q1. Write a program that takes the name and age of the user as input and displays a message whether the user is eligible to apply for a driving license or not.(the eligible age is 18 years).

Ans.

nm = input("Enter your name")
age = int(input("Enter your age"))
if age >= 18:
     print("You are eligible for driving licence")
else:
     print("You are not eligible for driving licence")

Q2. Write a function to print the table of a given number. The number has to be entered by the user.

Ans. 

def table(n):
   for i in range(1, 11):
     print("7 * ", i," =", n*i)

num = int(input("Enter any number"))
table(num)

OUTPUT : (If number entered by user is 7)

7 *  1  = 7
7 *  2  = 14
7 *  3  = 21
7 *  4  = 28
7 *  5  = 35
7 *  6  = 42
7 *  7  = 49
7 *  8  = 56
7 *  9  = 63
7 *  10  = 70

Q3. Write a program that prints minimum and maximum of five numbers entered by the user.

Ans. 

num1 = int(input("Enter any number"))
 max=num1
 min=num1
 for i in range(4):
   num = int(input("Enter any number"))
   if max < num:     max = num   if min > num:
     min=num
 print("Minimum number is :",min)    
 print("Maximum number is :",max)

Q4. Write a program to check if the year entered by the user is a leap year or not.

Ans. 

yr = int(input("Enter any year"))
    if yr%100 == 0:
       if yr%400 == 0:
           print("Leap Year")
       else:
           print("Not a Leap Year")
    elif yr%4 == 0:
       print("Leap Year")
    else:
       print("Not a Leap Year")

Flow of Control in Python Class 11

Q5. Write a program to generate the sequence: –5, 10, –15, 20, –25….. upto n, where n is an integer input by the user.

Ans. 

num = int(input("Enter any number"))
    for i in range(1,num + 1):
        if i%2 == 0: 
            print(5 *i, end = " , ")   
        else:     
            print(5*i*(-1), end = " , ")

Q6. Write a program to find the sum of 1+ 1/8 +1/27……1/n3, where n is the number input by the user.

Ans. 

num = int(input("Enter any number"))
sum = 0
for i in range(1,num + 1):
   sum = sum + 1/i**3
print("Sum of series is : ", sum)

Q7. Write a program to find the sum of digits of an integer number, input by the user.

Ans. 

num = int(input("Enter any number"))
sum = 0
while(num):
   r = num % 10
   sum = sum + r
   num = num // 10
print("Sum of the digit is : ",sum)

Q8. Write a function that checks whether an input number is a palindrome or not.

Ans. 

num = input("Enter any number")
rnum=num[: : -1]
if num == rnum:
     print("Palindrome")
else:
     print("Not a Palindrome")

OR

num = int(input("Enter any number"))
rnum = 0
r = 0
onum = num
while(num):
   r = num % 10
   rnum = rnum * 10 + r
   num = num // 10
if onum == rnum :
   print("Palindrome")
else :
   print("Not Palindrome")

Flow of Control in Python Class 11

Q9. Write a program to print the following patterns:

Ans i)

n = 3
for i in range (1, n + 1):
     sp = (n - i) * " "
     sym =  (2 * i - 1) * "*"
     print(sp, sym)
for j in range(n - 1, 0, -1):
     sp = (n - j) * " "
     sym = (2 * j - 1)* "*"
     print(sp, sym)

ii)

num = 5
for i in range (1, num + 1):
     sp = (num - i) * "  "
     print(sp, end = " ")
     for k in range(i, 1, -1):
         print(k, end = " ")
     for j in range(1, i + 1):
         print(j, end = " ")
     print()

iii)

str = "123456"
for i in (str):
   print(" " * int(i) + str[0 : len(str) - int(i)])

OR

num = 5
for i in range (num, 0, -1):
     sp = (num - i) * "  "
     print(sp, end=" ")
     for k in range(1, i + 1):
           print(k, end=" ")
     print()

iv)

num = 3
k = 0
for i in range (1, num + 1):
     sp = (num - i)*" "
     print(sp, end=' ')
     while (k != (2 * i - 1)) :
         if (k == 0 or k == 2 * i - 2) : 
             print("*", end= "")          
         else :              
             print(" ", end = "")          
         k = k + 1     
     k = 0     
     print( ) 
for j in range (num - 1, 0, -1):     
     sp = (num - j) * " "
     print(sp, end=" ")
     k = (2 * j - 1)
     while (k > 0) :
         if (k==1 or k == 2 * j - 1):             
             print("*",end="")
         else:
             print(" ",end="")
         k = k - 1
     print( ) 

Q10. Write a program to find the grade of a student when grades are allocated as given in the table below. Percentage of the marks obtained by the student is input to the program.

Percentage of Marks	Grade
Above 90%	A
80% to 90%	B
70% to 80%	C
60% to 70%	D
Below 60%	E

Ans.

per = int(input("Enter the Percentage"))
if per > 90:
   gr="A"
elif per > 80 and per <= 90:   
   gr = "B" 
elif per > 70 and per <= 80:   
   gr = "C" 
elif per >= 60 and per <= 70:
   gr = "D"
elif per < 60:
   gr = "E"
print("Grade is : ", gr)

Case Study-based Questions

Q1. Write a menu driven program that has options to

1. Accept the marks of the student in five major subjects in Class X

and display the same.
2. Calculate the sum of the marks of all subjects. Divide the total

marks by number of subjects(i.e. 5), calculate percentage = total

marks/5 and display the percentage.

3. Find the grade of the student as per the following criteria:

Criteria	Grade
percentage > 85	A
percentage < 85 && percentage >= 75	B
percentage < 75 && percentage >= 50	C
percentage > 30 && percentage <= 50	D
percentage <30	Reappear

Ans. 

ch='y'
while (ch=='y'):
  print("Menu Driven Program")
  print("1. Enter Marks of Five Subjects")
  print("2. Calculate Percentage")
  print("3. Calculate Grade")
  print("4. Exit")
  num = int(input("Enter Your Choice"))
  if num == 1 :
     en = int(input("Enter marks of English"))
     m = int(input("Enter marks of Mathematics"))
     sc = int(input("Enter marks of Science"))
     h = int(input("Enter marks of Hindi"))
     sst = int(input("Enter marks of SST"))
     print("Marks in English is :",en)
     print("Marks in Hindi is :",h)
     print("Marks in Mathematics is :",m)
     print("Marks in Science is :",sc)
     print("Marks in Social Studies is :",sst)
  if num == 2 :
     sum = en + m + sc + h + sst 
     per = sum/5 
     print("Percentage is ,", per)
  if num == 3 :
     if per >= 85 :
       print("Grade is A")
     elif per >= 75 and per < 85:       
       print("Grade is B")     
     elif per >= 50 and per < 75 :       
       print("Grade is C")     
     elif per > 30 and per < 50:
       print("Grade is D")
     elif per < 30:
       print("Reappear")
   if num == 4:
     exit()

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