CBSE Class 11 Computer Science Chapter 11: Conditional and Looping Constructs NCERT Solutions

Solution: The 'break' statement is used within loops (like 'for' or 'while') to terminate the loop's execution immediately. When the 'break' statement is encountered, the program control exits the loop entirely, and execution continues with the statement following the loop. This is useful when a certain condition is met and further iterations are unnecessary.

Solution: The output will be yes.

Here's the step-by-step evaluation:

1. The condition is x or y and z.
2. Python evaluates logical operators based on precedence: not, then and, then or.
3. First, y and z is evaluated: False and False results in False.
4. The condition becomes x or False, which is True or False.
5. True or False evaluates to True.
6. Since the condition is True, the code inside the if block is executed, printing "yes".

Solution: The output will be 3.

Let's trace the execution:

1. First if condition: not x or y evaluates to not True or False which is False or False, resulting in False. The first block is skipped.
2. First elif condition: not x or not y and z evaluates to not True or not False and False. Following precedence (not, then and, then or): False or True and False becomes False or False, which is False. This block is also skipped.
3. Second elif condition: not x or y or not y and x evaluates to not True or False or not False and True. Evaluating precedence: False or False or True and True becomes False or False or True. This simplifies to True.
4. Since this condition is True, the code inside this elif block is executed, printing 3. The subsequent else block is not checked.

Solution: The output will be True.

Explanation:

1. The code opens a file named "data.txt" in write mode ("w") within the loop using a with statement. This ensures the file is automatically closed when the block is exited.
2. The loop starts with i = 0.
3. For i = 0, i > 2 is False. The break is not executed. The with block finishes, and the file f is closed.
4. For i = 1, i > 2 is False. The with block finishes, and the file f is closed.
5. For i = 2, i > 2 is False. The with block finishes, and the file f is closed.
6. For i = 3, i > 2 is True. The break statement is executed, terminating the loop immediately.
7. After the loop terminates (either by finishing or breaking), the line print f.closed is executed. Since the with statement guarantees the file is closed upon exiting its block, and the last time the file was opened and closed was within the loop for i=2 (or earlier), f.closed will be True.

Solution: The numbers printed are 0, 1, 4, 5.

Explanation:

• The first loop uses range(2), which generates numbers starting from 0 up to (but not including) 2. So, it prints 0 and then 1.
• The second loop uses range(4, 6), which generates numbers starting from 4 up to (but not including) 6. So, it prints 4 and then 5.
• The numbers are printed sequentially as each loop completes.

Solution: The value printed is 13.

Let's analyze each condition:

1. if re.match(pattern, 'backup.txt'): sum += 1
   • re.match('back', 'backup.txt') checks if the string 'backup.txt' starts with 'back'. It does.
   • So, sum becomes 0 + 1 = 1.
2. if re.match(pattern, 'text.back'): sum += 2
   • re.match('back', 'text.back') checks if 'text.back' starts with 'back'. It does not.
   • So, sum remains 1.
3. if re.search(pattern, 'backup.txt'): sum += 4
   • re.search('back', 'backup.txt') checks if 'back' appears anywhere in 'backup.txt'. It does.
   • So, sum becomes 1 + 4 = 5.
4. if re.search(pattern, 'text.back'): sum += 8
   • re.search('back', 'text.back') checks if 'back' appears anywhere in 'text.back'. It does.
   • So, sum becomes 5 + 8 = 13.

Finally, print sum outputs 13.

Solution: The basic syntax for an 'if' statement in Python is:

if expression:

statement(s)

Here, expression is a condition that evaluates to either True or False. If the expression is True, the indented statement(s) below it are executed. If the expression is False, the indented statements are skipped.

Solution: The syntax for an 'if...else' statement in Python is:

if expression:

statement(s)_if_true

else:

statement(s)_if_false

In this structure, if the expression evaluates to True, the indented statement(s)_if_true are executed. If the expression evaluates to False, the indented statement(s)_if_false under the else block are executed. This provides two alternative paths for program execution based on the condition.