Page 271 - Computer Science Class 11 Without Functions
P. 271
11.6 Case Study
In this section, we will develop a module named stringFns.py that enables us to perform the following operations
on strings:
1. Form a string comprising distinct characters in a string, replacing uppercase characters with corresponding
lowercase characters.
2. Compute the number of matching characters in a pair of strings.
3. Find whether a string is a substring of another string.
4. Construct a string by reversing the sequence of the characters in the original string.
11.6.1 Distinct Characters in a String Ignoring the Case
To form a string comprising the distinct characters in a string, let us develop a program that takes a string, say str1,
as input from the user.
● Since a string may comprise a mix of upper and lowercase characters, we first construct a string of lowercase
characters (line 8).
● Next, we initialize the string of distinct characters (distinctChars) to an empty string (line 9).
● Next, for every character in the string, if the character is not included (not present) in the string distinctChars,
it is concatenated to distinctChars (lines 11-13).
● Finally, the program outputs a string (distinctChars) of distinct characters (line 15).
Program 11.1 Count the distinct characters in a given string.
01 '''
02 Objective: To determine unique characters in the given string
03 Input: str1 - string value
04 Output: string of unique characters
05 '''
06 myStr = input('Enter a String:')
07
08 myStr = myStr.lower()
09 distinctChars = ''
10
11 for ch in myStr:
12 if ch not in distinctChars:
13 distinctChars += ch
14
15 print(distinctChars)
11.6.2 The Number of Common Characters in a Pair of Strings
To compute the count of matching characters in a pair of strings, let us develop a program that takes a pair of strings,
str1 and str2, as input from the user.
● Since the two strings may comprise a mix of upper and lowercase characters, we construct strings that comprise the
same letters (in lowercase) of the English alphabet as the original strings (line 12).
● Next, we initialize a list distinctChar to empty list (line 14).
● The for loop (lines 15-17) scans the concatenation of strings str1 and str2.
● For every character in str1 + str2, we check whether the char is already present in distinctChar. If the
char is not present, we append the char in distinctChar (line 17).
● Finally, we print the length of the distinctChar, that is the number of distinct characters between str1 and str2
(line 19).
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