Strings – NCERT Class 11 Computer Science Chapter 8 – String Operations, Traversal, and Methods in Python

Explores strings as sequences of Unicode characters and their immutability in Python. Covers indexing, negative indexing, slicing, concatenation, repetition, membership operations, and traversal using loops. Introduces various built-in string methods like len(), count(), find(), replace(), and others, along with user-defined functions for string manipulation including palindrome checking and vowel replacement.

Updated: just now

Categories: NCERT, Class XI, Computer Science, Python, Strings, String Operations, String Methods, Chapter 8

Tags: Strings, String Operations, Indexing, Slicing, Concatenation, Repetition, Membership, String Traversal, Built-in Functions, User-defined Functions, Python Strings, Palindrome, NCERT Class 11, Computer Science, Chapter 8

Strings: NCERT Class 11 Chapter 8 - Enhanced Study Guide, Precise Notes, Diagrams & Quiz 2025

Enhanced Full Chapter Summary & Precise Notes from NCERT PDF (14 Pages)

Overview & Key Concepts

Exact Definition: "String is a sequence which is made up of one or more UNICODE characters."

Introduction: Sequences from Ch5 (strings/lists/tuples); Dicts as mapping. Focus: Strings detail; Immutable sequence.
Chapter Structure: Creation/accessing, Operations (concat/rep/mem/slice), Traversal, Methods/functions, Handling (programs).
2025 Relevance: Strings in NLP (e.g., tokenization); Data cleaning in pandas; Unicode for global text.

8.1 Introduction

Precise: Sequence: Ordered items indexed by integers. Strings: UNICODE chars (letters/digits/symbols/whitespace).

8.2 Strings

Precise: Enclose in ', ", '''; Multi-line with triple. Expanded: No char type; Len=1 string as char.

Precise Example 8.1: String Creation (SVG)

8.2.1 Accessing Characters

Precise: Indexing [0 to n-1]; Negative [-1 to -n]; len() for length. Expanded: IndexError out-of-range; Expr as index if int.

Precise Table 8.1: Indexing 'Hello World!' (SVG)

8.2.2 Immutability

Precise: Cannot change after creation; TypeError on assignment.

8.3 String Operations

Precise: + (concat), * (rep), in/not in (mem), [n:m] (slice). Expanded: Slice step k; Negative indices.

8.4 Traversing

Precise: for ch in str; while index < len(str).

8.5 Methods/Functions

Precise: len(), title(), lower(), upper(), count(), find(), index(), endswith(), startswith(), isalnum(), islower(), isupper(), isspace(), istitle(), lstrip(), rstrip(), strip(), replace(), join(), partition(), split().

8.6 Handling Strings

Precise: UDFs: charCount, replaceVowel, reverse print, reverse new str, checkPalin (Programs 8-1 to 8-5).

Enhanced Features (2025)

Full PDF integration, expanded programs (8-1 to 8-5), SVGs (indexing/slicing), detailed tables/examples, 30 Q&A updated, 10-Q quiz. Focus: String manipulation in Python.

Exam Tips

Predict outputs (slicing/indexing); Write UDFs (palindrome/reverse); List methods (Table 8.2); Explain immutability; Practice traversal/loops.

String Methods & Built-in Functions - Table 8.2 Expanded

Core: Manipulate strings (case, search, trim, etc.).

Key Methods (Detailed)

Case: lower(), upper(), title(), swapcase().
Search: find(), index(), count(), startswith(), endswith().
Check: isalnum(), islower(), isupper(), isspace(), istitle().
Modify: strip(), lstrip(), rstrip(), replace(), join(), split(), partition().

Method	Description	Example
len()	Returns length	len('Hello') → 5
title()	First letter upper	'hello world'.title() → 'Hello World'
lower()	All lower	'HELLO'.lower() → 'hello'
upper()	All upper	'hello'.upper() → 'HELLO'
count(str)	Occurrences	'Hello Hello'.count('Hello') → 2
find(str)	First index or -1	'Hello'.find('l') → 2
index(str)	First index or error	'Hello'.index('l') → 2
endswith(str)	True if ends with	'Hello!'.endswith('!') → True
startswith(str)	True if starts with	'Hello'.startswith('He') → True
isalnum()	Alnum only	'Hello123'.isalnum() → True
islower()	Lower or non-alpha	'hello'.islower() → True
isupper()	Upper or non-alpha	'HELLO'.isupper() → True
isspace()	Only spaces	' '.isspace() → True
istitle()	Title case	'Hello World'.istitle() → True
lstrip()	Remove left spaces	' Hello'.lstrip() → 'Hello'
rstrip()	Remove right spaces	'Hello '.rstrip() → 'Hello'
strip()	Remove both spaces	' Hello '.strip() → 'Hello'
replace(old, new)	Replace all	'Hello'.replace('l', '') → 'He*o'
join(iter)	Join with sep	'-'.join('Hello') → 'H-e-l-l-o'
partition(sep)	Split into 3	'India is Great'.partition('is') → ('India ', 'is', ' Great')
split(sep)	Split to list	'India is Great'.split() → ['India', 'is', 'Great']

Tip: 2025: str.format() for templating in web apps.

Handling Strings - Programs 8-1 to 8-5 Expanded

Core: UDFs for count, replace, reverse, palindrome.

Program 8-1: charCount(ch, st)

# Program 8-1
def charCount(ch, st):
    count = 0
    for character in st:
        if character == ch:
            count += 1
    return count

st = input("Enter a string: ")
ch = input("Enter the character: ")
count = charCount(ch, st)
print("Number of times", ch, "occurs:", count)

Output: Enter a string: Today is a Holiday
Enter the character: a
Number of times a occurs: 3

Program 8-2: replaceVowel(st)

# Program 8-2
def replaceVowel(st):
    newstr = ''
    for character in st:
        if character in 'aeiouAEIOU':
            newstr += '*'
        else:
            newstr += character
    return newstr

st = input("Enter a String: ")
st1 = replaceVowel(st)
print("Original:", st)
print("Modified:", st1)

Output: Enter a String: Hello World
Original: Hello World
Modified: H*ll* W*rld

Program 8-3: Reverse Print (No New String)

# Program 8-3
st = input("Enter a string: ")
for i in range(-1, -len(st)-1, -1):
    print(st[i], end='')

Output: Enter a string: Hello World
dlroW olleH

Program 8-4: reverseString(st)

# Program 8-4
def reverseString(st):
    newstr = ''
    length = len(st)
    for i in range(-1, -length-1, -1):
        newstr += st[i]
    return newstr

st = input("Enter a String: ")
st1 = reverseString(st)
print("Original:", st)
print("Reversed:", st1)

Output: Enter a String: Hello World
Original: Hello World
Reversed: dlroW olleH

Program 8-5: checkPalin(st)

# Program 8-5
def checkPalin(st):
    i = 0
    j = len(st) - 1
    while i <= j:
        if st[i] != st[j]:
            return False
        i += 1
        j -= 1
    return True

st = input("Enter a String: ")
result = checkPalin(st)
if result:
    print("The string", st, "is a palindrome")
else:
    print("The string", st, "is not a palindrome")

Output 1: Enter a String: kanak
The string kanak is a palindrome
Output 2: Enter a String: computer
The string computer is not a palindrome

Tip: 2025: Use str[::-1] for simple reverse in data processing.

30 Questions & Answers - NCERT Precise (Updated with Full Exercises)

Expanded: Based on NCERT Exercises. 10 (1-mark: Outputs from Q1), 10 (4-marks: Outputs/Explanations from Q2), 10 (8-marks: Programming Problems with Code). Full questions and mark-appropriate answers.

1-Mark Questions (10 Questions: Outputs from Exercise Q1 - mySubject = "Computer Science")

Q1: What is the output of print(mySubject[0:len(mySubject)])?

Ans: Computer Science (Full string from index 0 to end).

Q2: What is the output of print(mySubject[-7:-1])?

Ans: Scienc (Substring from negative index -7 to -1 exclusive).

Q3: What is the output of print(mySubject[::2])?

Ans: Cmue cec (Every second character from start to end).

Q4: What is the output of print(mySubject[len(mySubject)-1])?

Ans: e (Last character).

Q5: What is the output of print(2*mySubject)?

Ans: Computer ScienceComputer Science (String repeated twice).

Q6: What is the output of print(mySubject[::-2])?

Ans: eniSrtpo (Every second character from end to start).

Q7: What is the output of print(mySubject[:3] + mySubject[3:])?

Ans: Computer Science (Concatenation of first 3 and rest, reconstructs original).

Q8: What is the output of print(mySubject.swapcase())?

Ans: cOMPUTER sCIENCE (Swaps case of all letters).

Q9: What is the output of print(mySubject.startswith('Comp'))?

Ans: True (Starts with 'Comp').

Q10: What is the output of print(mySubject.isalpha())?

Ans: False (Contains space, not purely alphabetic).

4-Mark Questions (10 Questions: Outputs/Explanations from Exercise Q2 - myAddress = "WZ-1,New Ganga Nagar,New Delhi")

Q11: What is the output of print(myAddress.lower())? Explain briefly.

Ans: wz-1,new ganga nagar,new delhi. Converts all uppercase to lowercase; non-letters unchanged. (4 marks: Output + 1 sentence explanation).

Q12: What is the output of print(myAddress.upper())? Explain briefly.

Ans: WZ-1,NEW GANGA NAGAR,NEW DELHI. Converts all lowercase to uppercase. (4 marks: Output + explanation).

Q13: What is the output of print(myAddress.count('New'))? Explain.

Ans: 2. Counts non-overlapping occurrences of 'New'. (4 marks: Output + how count works).

Q14: What is the output of print(myAddress.find('New'))? Explain.

Ans: 5. Returns lowest index of first occurrence; -1 if not found. (4 marks: Output + method behavior).

Q15: What is the output of print(myAddress.rfind('New'))? Explain.

Ans: 21. Returns highest index of occurrence. (4 marks: Output + difference from find).

Q16: What is the output of print(myAddress.split(','))? Explain.

Ans: ['WZ-1', 'New Ganga Nagar', 'New Delhi']. Splits on comma into list. (4 marks: Output + splitting logic).

Q17: What is the output of print(myAddress.split(' '))? Explain.

Ans: ['WZ-1,New', 'Ganga', 'Nagar,New', 'Delhi']. Splits on space; default whitespace. (4 marks: Output + default behavior).

Q18: What is the output of print(myAddress.replace('New','Old'))? Explain.

Ans: WZ-1,Old Ganga Nagar,Old Delhi. Replaces all 'New' with 'Old'. (4 marks: Output + replacement rule).

Q19: What is the output of print(myAddress.partition(','))? Explain.

Ans: ('WZ-1', ',', 'New Ganga Nagar,New Delhi'). Partitions into tuple at first ','. (4 marks: Output + 3-part structure).

Q20: What is the output of print(myAddress.index('Agra'))? Explain.

Ans: ValueError: substring not found. Raises error if substring absent (unlike find's -1). (4 marks: Output + error vs find).

8-Mark Questions (10 Questions: Programming Problems from NCERT - With Full Code & Explanation)

Q21: Write a program to input line(s) of text until enter, count characters (incl spaces), alphabets, digits, symbols, words (space-separated). (8 marks)

Ans: Use loop for input; counters with isalpha/isalnum/isdigit/not; split for words.

# Program for text analysis
text = ''
while True:
    line = input()
    if line == '':
        break
    text += line + ' '
total_chars = len(text)
alphabets = sum(1 for c in text if c.isalpha())
digits = sum(1 for c in text if c.isdigit())
symbols = total_chars - alphabets - digits - text.count(' ')
words = len(text.split())
print(f"Chars: {total_chars}, Alphabets: {alphabets}, Digits: {digits}, Symbols: {symbols}, Words: {words}")

Explanation: Loop accumulates text; counters use built-ins; split() for words. (8 marks: Code + logic + sample output).

Q22: Write UDF to convert multi-word string to title case (param string). Explain. (8 marks)

Ans: Use .title() method.

def toTitle(s):
    return s.title()
st = input("Enter string: ")
print(toTitle(st))

Explanation: title() capitalizes first letter of each word. Handles multiple words automatically. (8 marks: Code + method use + example).

Q23: Write deleteChar(str, char) UDF to delete all occurrences of char, return new string. Explain. (8 marks)

Ans: Loop/build new string skipping char.

def deleteChar(st, ch):
    newstr = ''
    for c in st:
        if c != ch:
            newstr += c
    return newstr
st = input("String: ")
ch = input("Char: ")
print(deleteChar(st, ch))

Explanation: Iteration skips matches; immutable strings require new build. (8 marks: Code + immutability note).

Q24: Input string with digits; UDF to return sum of digits. Explain. (8 marks)

Ans: Loop check isdigit, add int(c).

def sumDigits(st):
    total = 0
    for c in st:
        if c.isdigit():
            total += int(c)
    return total
st = input("String: ")
print(sumDigits(st))

Explanation: isdigit() identifies; int() converts for sum. (8 marks: Code + type conversion).

Q25: UDF takes sentence, replaces spaces with '-', returns modified. Explain. (8 marks)

Ans: Replace ' ' with '-'.

def replaceSpaces(sent):
    return sent.replace(' ', '-')
sent = input("Sentence: ")
print(replaceSpaces(sent))

Explanation: replace() method for all occurrences. (8 marks: Code + method efficiency).

Q26: Explain indexing with positive/negative examples from 'Hello World!'. (8 marks)

Ans: Positive: [0]='H', [6]='W'; Negative: [-1]='!', [-12]='H'. len=12. Table 8.1. Immutability prevents change. (8 marks: Examples + diagram description + errors).

Q27: Detail slicing [n:m:k] with examples. Explain step/negative. (8 marks)

Ans: [1:5]='ello'; [::2]='HloWr'; [::-1]=reverse. Negative slices from end. (8 marks: 3 examples + syntax + edge cases).

Q28: Describe 5 string methods (e.g., lower, find, replace) with code examples. (8 marks)

Ans: lower(): 'HELLO'.lower()='hello'; find(): 'Hello'.find('l')=2; replace(): 'Hello'.replace('l','*')='He**o'. Etc. (8 marks: Methods + outputs + uses).

Q29: Write UDF charCount like Prog 8-1; explain loop. (8 marks)

Ans: As in Prog 8-1. Loop iterates each char, increments if match. Returns count. (8 marks: Code + traversal explanation).

Q30: Explain palindrome check (Prog 8-5); write similar for reverse. (8 marks)

Ans: Two pointers i=0, j=len-1; compare while i<=j. For reverse: range(-1,-len-1,-1). (8 marks: Logic + code snippet + efficiency).

Tip: Practice outputs; Write UDFs for programming probs.

Concept	Precise Description	Example	Process/2025 Note
Creation	Quotes enclose chars	'Hello'	Triple multi-line
Indexing	[0 to n-1]; [-n to -1]	str[0] → 'H'	len() for bound
Immutability	No change post-create	str[1]='a' Error	New str for mod
Operations	+ * in [n:m:k]	'Hi'*2 → 'HiHi'	Slice step
Traversal	for/while loops	for ch in str	Access each char
Methods	Built-in manip	str.lower()	Table 8.2
Handling	UDF programs	checkPalin	Reverse/palin

This article has been published in CBSE Class 11 Annual Assessment. Explore everything related to it here.

Group Discussions

No forum posts available.

Easily Share with Your Tribe