Character and String Data Types — Programming Examples

Use these short, runnable examples as demonstration checkpoints. Ask students to predict the output before you run each one.

1. Character data, digits vs. numbers, and output format

first_initial = "N"
middle_initial = "L"
first_digit = "2"
second_digit = "5"

# Digits in quotes are characters, so + glues them together
print(first_digit + second_digit)

# Without quotes they are integers, so + adds them
print(2 + 5)

# Three ways to format character output
print(first_initial + " " + middle_initial)   # space inserted with a string literal
print(first_initial, middle_initial)          # comma adds a space automatically
print(first_initial)                          # one print() per line
print(middle_initial)

Teaching point: A character is a single letter, digit, or symbol stored in quotes. “2” and “5” are characters, so + concatenates them into 25, while 2 + 5 adds integers to 7. Use a “ “ literal, a comma in print(), or separate print() calls to control how characters appear.

2. Character methods: checking and changing case

initial = input("Enter your middle initial: ")
initial = initial.upper()

print("Stored initial:", initial)
print("Is a letter?", initial.isalpha())
print("Is a digit?", initial.isdigit())
print("Lowercase version:", initial.lower())

section = "3"
print("Section is a letter?", section.isalpha())
print("Section is a digit?", section.isdigit())

Teaching point: Methods are applied with a period after the variable, as in initial.upper(). isalpha() and isdigit() return True or False, and upper()/lower() return a new value, so the result must be stored back in a variable to keep it.

3. String literals, escape sequences, and indexes

course_title = "Programming in Python"
quote = "My instructor said, \"Indexes start at zero.\""
file_path = "C:\\Users\\student\\lab05.py"

print(quote)
print(file_path)
print("Name\tGrade\nAva\tA\nBen\tB")

# Each character has an index, starting at [0]
print(course_title[0])    # P
print(course_title[3])    # g
print(course_title[15])   # P (the P in Python)

Teaching point: A backslash starts an escape sequence: " embeds a quotation mark, \ a backslash, \n a new line, and \t a tab. Every character in a string has an index starting at [0], and spaces count as characters, which is why the P in Python is at index 15.

4. String functions, case sensitivity, and substrings

book_title = "programming with python"
search_term = "PYTHON"

print(len(book_title))
print(book_title.title())
print(book_title.upper())
print(book_title.count("o"))
print(book_title.find("w"))
print(book_title.find("java"))
print(book_title.startswith("pro"))
print(book_title.endswith("python"))

# Case sensitivity: the same word in different case does not match
print("python" == search_term)
print("python" == search_term.lower())

# Substrings: [start:end] stops BEFORE the end index
first_word = book_title[0:11]
last_word = book_title[17:23]
print(first_word)
print(last_word)

Teaching point: len() is a function (the string goes inside the parentheses), while the others are methods. find() returns the index of the first match or -1 if there is none. “python” and “PYTHON” have different ASCII codes, so convert both to the same case before comparing. A substring [start:end] includes start but stops before end.

5. Concatenation and typecasting: student record builder

first_name = input("First name: ")
last_name = input("Last name: ")
student_id = 4127
due_date = "21 October"

# Concatenate variables into a new variable
full_name = last_name + ", " + first_name

# str() typecasts the integer so it can be concatenated
# (full_name + " #" + student_id would raise a TypeError)
record = full_name + " #" + str(student_id)
print(record)

# int() typecasts a substring of digits so it can be used in math
day = int(due_date[0:2])
late_day = day + 2
print("Due " + due_date + ", accepted late until " + str(late_day) + due_date[2:])

Build sequence:

1. Start with hard-coded first and last names and print full_name.
2. Replace them with input().
3. Try concatenating student_id directly to see the TypeError, then fix it with str().
4. Slice the day out of due_date, convert it with int(), and add 2.

Exit-ticket prompts

1. What does print(“4” + “7”) output, and why?
2. Write a string literal that prints: She said “Hi”
3. Given word = “Alphabet”, what is word[2]?
4. What does “banana”.find(“n”) return?
5. Fix the error: age = 19; print(“Age: “ + age)

Answer key

1. 47, because both values are characters, so + concatenates instead of adding
2. “She said "Hi"”
3. p
4. 2
5. print(“Age: “ + str(age))