NCERT Book Class 11 Computer Science Chapter 8 Strings PDF

Strings is the chapter where Class 11 Computer Science students learn to pull a program apart one character at a time. The ncert book class 11 computer science chapter 8 strings file on this page is the official NCERT chapter for 2026-27. Download it for the indexing table, the full built-in function list and all five solved programs.

• Chapter: Chapter 8, Strings
• Book: Computer Science, the Class 11 NCERT textbook for 2026-27, 11 chapters
• File: 14 pages, printed pages 175 to 188, the complete official chapter

You can page through the indexing table, the twenty built-in functions and every shell example in the viewer above before downloading.

This is the official NCERT chapter file for the 2026-27 session, hosted by Collegedunia with no pages removed.

How the Strings Chapter Is Laid Out

The chapter opens with a line from Bill Gates about the computer notebook, then moves through six numbered sections. Each one adds a small skill, and the last section puts all of them together inside working programs.

What the Strings Chapter PDF Contains

The PDF holds the whole chapter exactly as NCERT printed it, with nothing trimmed.

• All six sections, from the definition of a string to the five solved programs
• Table 8.1, the indexing chart that lays positive indices 0 to 11 above the phrase Hello World! and negative indices -12 to -1 below it
• Table 8.2, the long built-in function table with 20 methods, each with a description and real shell output
• Every shell example from Example 8.1 onward, including the error messages Python actually prints
• Programs 8-1 to 8-5 with their input prompts and printed output
• The Summary page, both exercise questions with ten parts each, and the five programming problems

Strings Class 11 Chapter Overview

Source: Magnet Brains on YouTube

How a String Is Created and Why It Cannot Be Changed

Section 8.2 defines a string as a sequence made of one or more Unicode characters. A character here can be a letter, a digit, a whitespace or any other symbol. You create one by wrapping those characters in quotes, and Python accepts three quoting styles.

• Single quotes: the everyday form, as in str1='Hello World!'
• Double quotes: the same result, useful when the text itself contains an apostrophe
• Triple quotes: either three single or three double quotes, and these are the only ones that let the text run across more than one line

The chapter adds a margin note that students often miss. Python has no separate character data type, so a string of length one is the character. That single line answers a common one mark question.

Section 8.2.2 then states the rule that shapes everything else in the chapter. A string is immutable, so its contents cannot be changed after it has been created. Trying to swap one letter with str1[1] = 'a' does not quietly work, it raises a TypeError saying that a str object does not support item assignment. This is why Program 8-2 builds a brand new string when it replaces vowels instead of editing the old one in place.

Indexing, Negative Indices and the len Function

Section 8.2.1 explains how to reach one character at a time. The index goes inside square brackets, the first character from the left is at index 0, and the last one is at n-1 where n is the length of the string. An index beyond that range gives an IndexError.

The index may also be an expression, so str1[2+4] is valid because 2+4 evaluates to an integer. A float index such as str1[1.5] is not, and Python answers with a TypeError saying string indices must be integers. Negative indices then let you count from the right instead, with -1 at the last character and -n at the first.

The built-in len() function is introduced here because the two index systems are tied to it. Once n = len(str1), the last character is str1[n-1] and the first is str1[-n]. Table 8.1 in the PDF prints both index rows above and below the phrase, which is the quickest way to fix the pattern in memory.

Concatenation, Repetition and Membership Operators

Section 8.3 lists the operations Python allows on strings. Three of them are single symbol operators you have already met on numbers, doing something different here.

• Concatenation with +: 'Hello' + 'World!' returns 'HelloWorld!' as one new value. Note that no space is inserted, and both original strings stay exactly as they were
• Repetition with *: str1 * 2 on 'Hello' returns 'HelloHello', and str1 * 5 repeats it five times. Again the original is untouched, because the string is immutable
• Membership with in: takes two strings and returns True when the first appears as a substring inside the second, so 'Wor' in 'Hello World!' is True but 'My' in it is False
• Membership with not in: the exact reverse, so 'My' not in 'Hello World!' returns True while 'Hello' not in it returns False

Both membership operators return a Boolean, which is why they slot straight into an if statement. Program 8-2 uses this in one line, checking if character in 'aeiouAEIOU' to decide whether a letter is a vowel. Comparison operators such as == and != also work on strings and compare them character by character, and the palindrome program in section 8.6 depends on exactly that.

Slicing a String and Traversing It with Loops

Slicing pulls out a whole substring in one step. Given a string str1, the slice str1[n:m] returns the characters from index n up to but not including index m, so the length of the result is always m minus n. This asymmetry is the single most common source of lost marks in the chapter.

Section 8.4 then covers traversal, which means visiting every character in turn. The chapter gives two versions of the same job, and the exercise expects you to be able to write both.

• The for loop: for ch in str1 hands you one character per pass and stops on its own at the end. Nothing has to be counted
• The while loop: set index = 0, run while index < len(str1), print str1[index] and add one each time. You control the counter yourself
• Printing on one line: both versions pass end='' to print so the characters appear side by side rather than one per line

String Methods and Built-in Functions in Table 8.2

Section 8.5 is the longest part of the chapter and the part exercise question 2 tests directly. Table 8.2 lists twenty entries, and each row carries a description plus a small block of real shell output. They fall into four natural groups.

A few rows carry the traps that examiners like. find() returns -1 when the substring is absent, while index() does the same job but raises a ValueError instead. That single difference is the most asked one mark question from this chapter. Both accept an optional start and end, so str1.count('Hello',12,25) searches only that slice of the string.

The content tests also have edges worth remembering. isalnum() is True for letters and digits together but False the moment a space or a symbol appears. islower() stays True for 'hello 1234' because the digits are not alphabets and the letters that are present are lowercase, yet it turns False for '1234' alone since no alphabet is present at all. The reshaping group is just as precise. partition() always returns three parts, namely the text before the separator, the separator itself and the text after it, while split() returns a list of words and uses spaces when you give it no delimiter. The exercise also touches isalpha() and swapcase() in question 1, so the two lists are worth reading together.

The Five Solved Programs and the Exercise Set

Section 8.6 turns everything above into complete code. Each program defines its own function, takes input from the user and prints an answer, so they double as practice for the functions chapter.

• Program 8-1: charCount() counts how many times one character appears in a string, using a for loop and a running counter
• Program 8-2: replaceVowel() builds a new string and swaps every vowel for a star, checking membership against 'aeiouAEIOU'
• Program 8-3: prints a string backwards without making a new one, by running range(-1,-len(st)-1,-1) over negative indices
• Program 8-4: reverseString() does the same job but stores the reversed text in a new string and returns it
• Program 8-5: checkPalin() walks two pointers inward from both ends and returns False the moment a pair fails to match

The exercise that follows has two questions with ten parts each, so 20 outputs to work out by hand. Question 1 uses mySubject="Computer Science" and tests slicing, the step size, repetition, swapcase(), startswith() and isalpha(). Question 2 uses a Delhi address string and tests lower(), upper(), count(), find(), rfind(), split(), replace(), partition() and index(). The last part is deliberately unfair, asking for index('Agra') on a string that does not contain it, which raises a ValueError. Five programming problems close the chapter, covering character counting, title case conversion, character deletion, digit sums and replacing spaces with hyphens.

What Collegedunia Adds to This Chapter PDF

Collegedunia gives students the file plus a way into it. The chapter PDF is the official NCERT file, untouched.

• Official file: the exact NCERT chapter PDF, no pages removed
• Read in the browser: page through all 14 pages first
• Chapter list: jump to any other chapter from one table

Also Check: the other Class 11 Computer Science resources for this chapter.

Class 11 Computer Science NCERT Book PDF: All Chapters

Every chapter of the book is on its own page. The 2026-27 Class 11 Computer Science textbook has 11 chapters, and chapters 5 to 10 form the Python programming block.

Strings Class 11 NCERT Book PDF FAQs