Question 1

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

Accepted Answer

The 'else' construct in an if statement is used to specify a block of code that will execute if the condition(s) in the if and elif statements are false. It acts as a default case. The 'elif' (else if) construct allows checking multiple conditions sequentially. If the first if condition is false, the program checks the elif condition(s) one by one. If any elif condition is true, its block executes, and the rest are skipped. Else is used only once at the end, while multiple elifs can be used between if and else. — In an if-elif-else ladder, the program evaluates conditions from top to bottom. 'elif' allows multiple conditions to be checked in sequence, whereas 'else' handles all cases not covered by if or elif. For example:

if condition1:
    # block1
elif condition2:
    # block2
else:
    # block3

If condition1 is false and condition2 is true, block2 runs. If both are false, block3 runs.

Question 2

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

Accepted Answer

The range() function is used to generate a sequence of numbers. It is commonly used in for loops to iterate over a sequence of numbers. The function can take one, two, or three arguments: start, stop, and step. It generates numbers from start (inclusive) to stop (exclusive), incremented by step.

Example:
for i in range(1, 5):
    print(i)

This will print numbers 1, 2, 3, 4. — range() helps in creating a list of numbers without manually writing them. It is efficient and widely used in loops. The default start is 0, and default step is 1 if not provided.

Example with all parameters:
range(2, 10, 2) generates 2, 4, 6, 8.

Question 3

Differentiate between break and continue statements using examples.

Accepted Answer

Break and continue are control statements used inside loops.

- break: Terminates the loop immediately and transfers control to the statement following the loop.
- continue: Skips the current iteration and moves to the next iteration of the loop.

Example of break:
for i in range(5):
    if i == 3:
        break
    print(i)
# Output: 0 1 2

Example of continue:
for i in range(5):
    if i == 3:
        continue
    print(i)
# Output: 0 1 2 4 — In the break example, when i becomes 3, the loop stops entirely. In the continue example, when i is 3, the print statement is skipped for that iteration, but the loop continues with i=4.

Question 4

What is an infinite loop? Give one example.

Accepted Answer

An infinite loop is a loop that never terminates because its condition always remains true. It keeps executing indefinitely unless externally interrupted.

Example:
while True:
    print("This loop runs forever") — In the example, the condition 'True' is always true, so the loop never ends. Infinite loops are generally undesirable unless intentionally used for specific purposes like servers waiting for requests.

Question 5

Find the output of the following program segments:

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

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

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

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

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

(vi) 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!")

Accepted Answer

(i) Code: a = 110 while a > 100: print(a) a -= 2 Output: 110 108 106 104 102 Explanation: Starts at 110, prints and decrements by 2 until a <= 100. (ii) Code: for i in range(20,30,2): print(i) Output: 20 22 24 26 28 Explanation: range(20,30,2) generates numbers from 20 to 28 stepping by 2. (iii) Code: country = 'INDIA' for i in country: print(i) Output: I N D I A Explanation: Iterates over each character in the string and prints it. (iv) Code: i = 0 sum = 0 while i < 9: if i % 4 == 0: sum = sum + i i = i + 2 print(sum) Output: 8 Explanation: Values of i: 0,2,4,6,8 (since i increments by 2) Only i values divisible by 4 (0,4,8) are added to sum. Sum = 0 + 4 + 8 = 12 but note i increments inside loop, careful with indentation. But as per code, i increments by 2 each time, sum adds i if i%4==0. So i=0 (sum=0), i=2 (no add), i=4 (sum=4), i=6 (no add), i=8 (sum=12) Print sum = 12 (v) Code: for x in range(1,4): for y in range(2,5): if x * y > 10: break print(x * y) Output: 2 3 4 4 6 8 6 8 Explanation: For each x, y iterates from 2 to 4. If product > 10, inner loop breaks. Prints product otherwise. (vi) Code: 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!") Output: Current variable value: 7 Good bye! Current variable value: 5 Good bye! Current variable value: 4 Good bye! Current variable value: 3 Explanation: - Starts with var=7 - Prints var, decrements var - If var==6, decrements var again and continues (skips print "Good bye!") - If var==3, breaks loop - Otherwise prints "Good bye!" Stepwise: var=7: print var=7, var=6, var==6 true, var=5, continue (skip "Good bye!") var=5: print var=5, var=4, var!=3 or 6, print "Good bye!" var=4: print var=4, var=3, var!=6, print "Good bye!" var=3: print var=3, var=2, var==3 triggers break, loop ends. — Detailed explanation is provided above for each sub-part showing how the loops and conditions work to produce the output.

Question 6

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

Accepted Answer

To find the sum of digits of an integer number input by the user, follow these steps:

1. Take the integer input from the user.
2. Initialize a variable sum to 0.
3. Use a loop to extract each digit of the number:
   - Find the last digit by taking the remainder when divided by 10 (digit = number % 10).
   - Add this digit to sum.
   - Remove the last digit by integer division by 10 (number = number // 10).
4. Repeat until the number becomes 0.
5. Print the sum.

Example Python code:

```python
number = int(input("Enter an integer number: "))
sum_digits = 0
while number > 0:
    digit = number % 10
    sum_digits += digit
    number = number // 10
print("Sum of digits is:", sum_digits)
```

This program correctly computes the sum of digits of the input number. — The program extracts each digit from the number by repeatedly taking the remainder when divided by 10, adds it to a running total, and then removes the last digit by integer division. This process continues until all digits are processed, resulting in the sum of digits.

Question 7

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

[Note: A number or a string is called palindrome if it appears same when written in reverse order also. For example, 12321 is a palindrome while 123421 is not a palindrome]

Accepted Answer

To check whether a number is a palindrome:

1. Take the input number from the user.
2. Store the original number in a variable.
3. Reverse the number by extracting digits and constructing the reversed number.
4. Compare the reversed number with the original number.
5. If both are equal, the number is a palindrome; otherwise, it is not.

Example Python code:

```python
number = int(input("Enter a number: "))
original_number = number
reversed_number = 0
while number > 0:
    digit = number % 10
    reversed_number = reversed_number * 10 + digit
    number = number // 10
if original_number == reversed_number:
    print("The number is a palindrome.")
else:
    print("The number is not a palindrome.")
```

This program correctly identifies whether the input number is a palindrome. — The program reverses the number by extracting digits and building the reversed number. Then it compares the reversed number with the original number to determine if it is a palindrome.

Question 8

Write a program to print the following patterns:

i)  *
    ***
    ***
    ***
    ***
ii)  1
    2 1 2
    3 2 1 2 3
    4 3 2 1 2 3 4
    5 4 3 2 1 2 3 4 5

iii) 1 2 3 4 5
     1 2 3 4
     1 2 3
     1 2
     1

iv)  *
     *
     *
     *
     *
     *
     *
     *

Accepted Answer

To print the given patterns, write separate code blocks for each pattern:

(i) Pattern:
```
*
***
***
***
***
```
This can be printed by:
- Print '*' once in first line.
- Then print '***' four times in next four lines.

Example code:
```python
print("*")
for _ in range(4):
    print("***")
```

(ii) Pattern:
```
1
2 1 2
3 2 1 2 3
4 3 2 1 2 3 4
5 4 3 2 1 2 3 4 5
```
Explanation:
- For each line i from 1 to 5:
  - Print descending numbers from i down to 1.
  - Then print ascending numbers from 2 up to i.

Example code:
```python
for i in range(1, 6):
    for j in range(i, 0, -1):
        print(j, end=' ')
    for j in range(2, i+1):
        print(j, end=' ')
    print()
```

(iii) Pattern:
```
1 2 3 4 5
1 2 3 4
1 2 3
1 2
1
```
Explanation:
- For each line i from 5 down to 1:
  - Print numbers from 1 up to i.

Example code:
```python
for i in range(5, 0, -1):
    for j in range(1, i+1):
        print(j, end=' ')
    print()
```

(iv) Pattern:
```
*
*
*
*
*
*
*
```
Explanation:
- Print '*' seven times, each on a new line.

Example code:
```python
for _ in range(7):
    print("*")
```

These programs will print the required patterns as specified. — Each pattern is printed by nested loops controlling the number and order of elements printed per line. The logic for ascending and descending sequences is implemented using appropriate ranges in loops.

Question 9

Write a program to find the grade of a student when grades are allocated as given in the table below.

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

Percentage of the marks obtained by the student is input to the program.

Accepted Answer

To find the grade based on the percentage marks:

1. Take the percentage marks as input from the user.
2. Use if-elif-else statements to check the range in which the marks fall.
3. Print the corresponding grade.

Example Python code:

```python
marks = float(input("Enter the percentage of marks obtained: "))
if marks > 90:
    grade = 'A'
elif 80 <= marks <= 90:
    grade = 'B'
elif 70 <= marks < 80:
    grade = 'C'
elif 60 <= marks < 70:
    grade = 'D'
else:
    grade = 'E'
print("Grade:", grade)
```

This program correctly assigns grades based on the given criteria. — The program uses conditional statements to check the percentage range and assigns the grade accordingly. The ranges are checked in descending order to ensure correct grade allocation.

Question 10

Write a menu driven program that has options to - accept the marks of the student in five major subjects in Class X and display the same. - 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. - 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 |

Accepted Answer

Solution: 1. Accept marks of the student in five subjects. 2. Display the marks. 3. Calculate the sum of marks. 4. Calculate percentage = total marks / 5. 5. Display the percentage. 6. Determine grade based on percentage: - If percentage > 85, grade = 'A' - Else if percentage >= 75 and < 85, grade = 'B' - Else if percentage >= 50 and < 75, grade = 'C' - Else if percentage > 30 and <= 50, grade = 'D' - Else grade = 'Reappear' Sample Python code: ```python marks = [] for i in range(5): m = int(input(f"Enter marks for subject {i+1}: ")) marks.append(m) print("Marks entered:", marks) total = sum(marks) percentage = total / 5 print(f"Total marks: {total}") print(f"Percentage: {percentage}") if percentage > 85: grade = 'A' elif 75 <= percentage < 85: grade = 'B' elif 50 <= percentage < 75: grade = 'C' elif 30 < percentage <= 50: grade = 'D' else: grade = 'Reappear' print(f"Grade: {grade}") ``` Explanation: - The program first takes input marks for five subjects. - It calculates the total and percentage. - Then, it uses conditional statements to assign grades based on the given criteria. - Finally, it displays the marks, total, percentage, and grade. — Step-by-step solution: 1. Input marks for five subjects. 2. Sum the marks. 3. Calculate percentage = total / 5. 4. Use if-elif-else to assign grade based on percentage. 5. Display all results.

Question 11

Figure 6.1 shows a bus carrying students to school following a fixed route with no deviation. Which programming concept does this analogy best represent?

Accepted Answer

Sequence — The bus following a fixed route with no deviation represents the sequence concept in programming, where statements are executed one after another in the order they appear.

Question 12

What is the meaning of the term 'flow of control' in programming?

Accepted Answer

Flow of control is the order in which statements in a program are executed. For example, in Python, statements are executed one after another unless control structures like selection or repetition alter this order. — Flow of control refers to the sequence in which individual statements, instructions, or function calls are executed in a program. It determines how the program behaves and responds to different inputs or conditions.

Question 13

In Python, which control structures are primarily used to implement flow of control?

Accepted Answer

Selection and Repetition — Python uses selection (decision making) and repetition (loops) as primary control structures to alter the flow of execution beyond simple sequence.

Question 14

Explain why indentation is important in Python programming.

Accepted Answer

Indentation in Python defines blocks of code and controls the flow of execution. For example, in if-else statements or loops, proper indentation groups statements into blocks that execute together. — Python uses indentation instead of curly braces to define code blocks. The interpreter enforces consistent indentation, and incorrect indentation leads to syntax errors. Proper indentation improves code readability and ensures correct execution.

Question 15

Program 6-1 prints the difference of two numbers. What will be the output if the inputs are 5 and 7?

Accepted Answer

The difference of 5 and 7 is -2 — Program 6-1 calculates diff = num1 - num2, so with inputs 5 and 7, diff = 5 - 7 = -2.

Flow of Control

Flow of Control — Study Notes

6.1 INTRODUCTION

6.2 SELECTION

6.3 INDENTATION

Practice Questions — Flow of Control

All 11 Chapters in Computer Science