Flow of Control – Class 11 Computer Science notes, important questions and MCQs

Chapter overview

Flow of control is the order in which statements in a program are executed. Python supports sequential flow, selection using if, if-else and if-elif-else statements, and repetition using for and while loops. Indentation defines blocks of code in Python. Statements such as break and continue change the flow inside loops, and loops can be nested.

Selection

• The if statement executes a block only when its condition is True; if-else chooses between two blocks; if-elif-else chooses among many.
• Python uses indentation (usually 4 spaces) to mark a block; a colon ends the if, elif, else, for and while header lines.
• Conditions use relational and logical operators, for example if marks >= 33 and attendance >= 75.

Repetition

• The for loop iterates over a sequence; range(start, stop, step) generates numbers from start up to stop − 1, for example range(1, 6) gives 1, 2, 3, 4, 5 and range(10, 0, -2) gives 10, 8, 6, 4, 2.
• The while loop repeats as long as its condition is True; the condition must eventually become False to avoid an infinite loop.
• break exits the loop immediately; continue skips the rest of the current iteration; loops can be nested, as in printing patterns, where the inner loop completes for every iteration of the outer loop.

Key terms

Selection

choosing a block of code based on a condition

Iteration

repeating a block of code

Indentation

leading spaces that define a block in Python

break

a statement that terminates the loop

continue

a statement that skips to the next iteration

Important questions with answers

Quick revision

• Sequential flow and indentation.
• if, if-else, if-elif-else.
• for loop and range().
• while loop; break, continue; nested loops.

Exam tips

• Trace range() carefully: the stop value is not included.
• Always change the loop variable inside a while loop.

Practice MCQs

1. Python uses which of these to define blocks of code

   1. curly braces
   2. semicolons
   3. indentation
   4. brackets
   Show answer

   Answer: (c) indentation. Usually four spaces.

2. range(1, 5) generates

   1. 1, 2, 3, 4, 5
   2. 2, 3, 4, 5
   3. 0, 1, 2, 3, 4
   4. 1, 2, 3, 4
   Show answer

   Answer: (d) 1, 2, 3, 4. The stop value is excluded.

3. The statement that exits a loop immediately is

   1. break
   2. continue
   3. pass
   4. return
   Show answer

   Answer: (a) break. Control moves after the loop.

4. The output of for i in range(10, 0, -3): print(i, end=' ') is

   1. 9 6 3
   2. 10 7 4
   3. 10 7 4 1
   4. 10 7 4 1 -2
   Show answer

   Answer: (c) 10 7 4 1. Values stop before reaching 0.

5. The statement that skips the rest of the current iteration is

   1. break
   2. continue
   3. exit
   4. else
   Show answer

   Answer: (b) continue. The loop proceeds to the next iteration.

6. How many times does the body run in for i in range(2, 11, 2)

   1. 4
   2. 5
   3. 6
   4. 10
   Show answer

   Answer: (b) 5. Values are 2, 4, 6, 8, 10.

7. What is printed by: i = 1; while i < 10: i = i * 2; then print(i)

   1. 8
   2. 16
   3. 10
   4. 2
   Show answer

   Answer: (b) 16. i becomes 2, 4, 8, 16 and the loop stops.

8. In a nested loop where the outer loop runs 3 times and the inner loop runs 4 times for each, the inner body runs

   1. 7 times
   2. 12 times
   3. 3 times
   4. 4 times
   Show answer

   Answer: (b) 12 times. 3 × 4 = 12.