String functions overview in C++ - Mini Project: Build & Apply

String functions overview

📖 Scenario: You are working on a simple program that manages a list of fruit names. You want to learn how to use basic string functions in C++ to check lengths, find characters, and change case.

🎯 Goal: Build a program that creates a string, sets a character to uppercase, finds a character's position, and prints the length of the string.

📋 What You'll Learn

Create a string variable with a specific value

Create an integer variable to store the position of a character

Use string functions to find the length of the string

Use string functions to find the position of a character

Change a character in the string to uppercase

Print the results

💡 Why This Matters

🌍 Real World

String functions are used in many programs to process text, such as searching, formatting, and modifying user input.

💼 Career

Knowing basic string operations is essential for software development, data processing, and building user interfaces.

1

Create the string variable

Create a string variable called fruit and set it to the value "banana".

C++

#include 
#include 

int main() {

    // Create string variable fruit with value "banana"
    // Your code here

    return 0;
}

Hint

Use std::string to create the variable and assign the value "banana".

2

Create a variable to store character position

Create an integer variable called pos and set it to the position of the first letter 'a' in the string fruit using the find function.

C++

#include 
#include 

int main() {

    std::string fruit = "banana";

    // Find position of 'a' in fruit and store in pos
    // Your code here

    return 0;
}

Hint

Use fruit.find('a') to find the first occurrence of 'a'.

3

Change a character to uppercase

Change the character at position pos in fruit to uppercase using toupper from cctype. Include #include <cctype> at the top.

C++

#include 
#include 
#include 

int main() {

    std::string fruit = "banana";
    int pos = fruit.find('a');

    // Change character at pos to uppercase
    // Your code here

    return 0;
}

Hint

Use std::toupper to convert the character to uppercase and assign it back.

4

Print the results

Print the length of fruit using fruit.length() and print the modified fruit string. Use two separate std::cout statements.

C++

#include 
#include 
#include 

int main() {

    std::string fruit = "banana";
    int pos = fruit.find('a');
    fruit[pos] = std::toupper(fruit[pos]);

    // Print length of fruit
    // Print modified fruit string
    // Your code here

    return 0;
}

Hint

Use std::cout << fruit.length() << std::endl; and std::cout << fruit << std::endl; to print the results.

Practice

1. Which C++ string function returns the number of characters in a string?

easy

A. substr()

B. append()

C. length()

D. find()

Solution

1. Step 1: Understand string length function

   The length() function returns how many characters are in the string.

2. Step 2: Compare with other functions

   append() adds text, substr() extracts part, find() searches for text.

3. Final Answer:

   length() -> Option C

4. Quick Check:

   String length = length() [OK]

Hint: Length means count characters, use length() [OK]

Common Mistakes:

• Confusing length() with append()
• Using substr() to get length
• Thinking find() returns length

2. Which of the following is the correct syntax to add " world" to a string str in C++?

easy

A. str.append(" world");

B. str.add(" world");

C. str.concat(" world");

D. str.push_back(" world");

Solution

1. Step 1: Identify correct append syntax

   In C++, append() adds text to the end of a string: str.append(" world");.

2. Step 2: Check other options

   add() and concat() are not string methods in C++. push_back() adds a single character, not a string.

3. Final Answer:

   str.append(" world"); -> Option A

4. Quick Check:

   Use append() to add text [OK]

Hint: Use append() to add text, not add() or concat() [OK]

Common Mistakes:

• Using add() or concat() which don't exist
• Using push_back() with string argument
• Missing semicolon at end

3. What is the output of this C++ code?

std::string s = "hello world";
std::cout << s.substr(6, 5);

medium

A. worlds

B. hello

C. hello world

D. world

Solution

1. Step 1: Understand substr parameters

   substr(6, 5) means start at index 6 and take 5 characters.

2. Step 2: Extract substring from "hello world"

   Index 6 is 'w', next 5 characters are "world".

3. Final Answer:

   world -> Option D

4. Quick Check:

   substr(6,5) = "world" [OK]

Hint: Count from zero, substr(start, length) extracts text [OK]

Common Mistakes:

• Starting count at 1 instead of 0
• Taking wrong number of characters
• Confusing substr with find

4. Identify the error in this C++ code snippet:

std::string s = "example";
s = s.substr(3, 10);

medium

A. substr length exceeds string length but no error occurs

B. substr start index is invalid

C. substr requires two arguments but only one given

D. Cannot assign substr result to string variable

Solution

1. Step 1: Check substr parameters

   Start index 3 is valid. Length 10 is longer than remaining string length.

2. Step 2: Understand substr behavior with long length

   substr returns substring from index 3 to end without error even if length is too big.

3. Final Answer:

   substr length exceeds string length but no error occurs -> Option A

4. Quick Check:

   substr handles long length safely [OK]

Hint: substr length can be longer than string safely [OK]

Common Mistakes:

• Expecting runtime error for long length
• Thinking start index is invalid
• Confusing substr arguments count

5. Given a string text = "Hello C++ World", which code snippet converts it to all uppercase letters?

hard

A. text.toUpperCase();

B. for (auto &c : text) c = toupper(c);

C. text.upper();

D. transform(text.begin(), text.end(), text.begin(), tolower);

Solution

1. Step 1: Identify correct uppercase conversion

   Looping over each character and applying toupper() converts all letters to uppercase.

2. Step 2: Check other options

   toUpperCase() and upper() are not C++ string methods. transform(text.begin(), text.end(), text.begin(), tolower); uses tolower which converts to lowercase.

3. Final Answer:

   for (auto &c : text) c = toupper(c); -> Option B

4. Quick Check:

   Use loop + toupper() for uppercase [OK]

Hint: Use loop with toupper() to change case [OK]

Common Mistakes:

• Using non-existent string methods
• Using tolower instead of toupper
• Not using reference in loop to modify string