String functions overview in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the length of the string.

C++

#include <iostream>
#include <string>

int main() {
    std::string text = "Hello";
    std::cout << text.[1]() << std::endl;
    return 0;
}

Drag options to blanks, or click blank then click option'

AgetSize

Bsize

Ccount

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using a function that doesn't exist like count() or getSize()

The length() function returns the number of characters in the string.

2fill in blank

medium

Complete the code to convert the string to uppercase using a loop.

C++

#include <iostream>
#include <string>
#include <cctype>

int main() {
    std::string text = "hello";
    for (int i = 0; i < text.length(); ++i) {
        text[i] = [1](text[i]);
    }
    std::cout << text << std::endl;
    return 0;
}

Drag options to blanks, or click blank then click option'

Atoupper

BtoUpperCase

Cupper

Dtouppercase

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent functions like toUpperCase or upper

The toupper() function converts a character to uppercase.

3fill in blank

hard

Fix the error in the code to find the position of a character in the string.

C++

#include <iostream>
#include <string>

int main() {
    std::string text = "apple";
    size_t pos = text.[1]('p');
    std::cout << pos << std::endl;
    return 0;
}

Drag options to blanks, or click blank then click option'

Afind

BindexOf

Csearch

Dposition

Attempts:

3 left

💡 Hint

Common Mistakes

Using JavaScript-like functions such as indexOf

The find() function returns the index of the first occurrence of the character.

4fill in blank

hard

Fill both blanks to create a substring from index 1 to 3.

C++

#include <iostream>
#include <string>

int main() {
    std::string text = "banana";
    std::string part = text.[1]([2], 3);
    std::cout << part << std::endl;
    return 0;
}

Drag options to blanks, or click blank then click option'

Asubstr

Bsubstring

C1

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Using substring which is not a C++ string function

Wrong starting index

The substr() function extracts a substring starting at the given index. Here, starting at index 1 for length 3 gives "ana".

5fill in blank

hard

Fill all three blanks to replace 'cat' with 'dog' in the string.

C++

#include <iostream>
#include <string>

int main() {
    std::string text = "the cat sat";
    size_t pos = text.[1]("cat");
    if (pos != std::string::npos) {
        text.[2](pos, [3], "dog");
    }
    std::cout << text << std::endl;
    return 0;
}

Drag options to blanks, or click blank then click option'

Afind

Breplace

C3

Derase

Attempts:

3 left

💡 Hint

Common Mistakes

Using erase instead of replace

Wrong length for replacement

First, find() locates "cat". Then replace() replaces 3 characters starting at that position with "dog".

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