Character arrays in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a character array named name with space for 10 characters.

C++

char name[[1]];

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

A10

Bchar

C5

Dstring

Attempts:

3 left

💡 Hint

Common Mistakes

Using a data type like 'char' or 'string' inside the brackets instead of a number.

Forgetting to specify the size of the array.

The code declares a character array name with space for 10 characters using char name[10];.

2fill in blank

medium

Complete the code to initialize the character array word with the string "hello".

C++

char word[] = [1];

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

A'hello'

B"hello"

Chello

D'h','e','l','l','o'

Attempts:

3 left

💡 Hint

Common Mistakes

Using single quotes instead of double quotes for strings.

Not enclosing the string in any quotes.

To initialize a character array with a string, use double quotes like "hello". Single quotes are for single characters.

3fill in blank

hard

Fix the error in the code to correctly print the first character of the array letters.

C++

char letters[] = {'a', 'b', 'c'};
std::cout << letters[1] << std::endl;

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

A[0]

B(0)

C{0}

D<0>

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses or curly braces instead of square brackets.

Using an incorrect index like 1 instead of 0.

To access the first element of an array, use square brackets with the index: letters[0].

4fill in blank

hard

Fill both blanks to create a loop that prints each character in the array chars until the null character is found.

C++

char chars[] = {'C', '+', '+', '\0'};
for (int i = [1]; chars[i] [2] '\0'; i++) {
    std::cout << chars[i];
}

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

A0

B1

C!=

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Starting the loop at 1 instead of 0.

Using '==' instead of '!=' in the loop condition.

The loop starts at index 0 and continues while the character is not the null character '\0'.

5fill in blank

hard

Fill all three blanks to create a character array greeting initialized with "Hi!" and print its length excluding the null character.

C++

char greeting[] = [1];
int length = 0;
while (greeting[2] != '\0') {
    [3];
}
std::cout << length << std::endl;

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

A"Hi!"

B[length]

C++length

D[length++]

Attempts:

3 left

💡 Hint

Common Mistakes

Using single quotes for the string initialization.

Not incrementing the length variable correctly.

Using the wrong index syntax in the while condition.

The array is initialized with "Hi!". The loop uses greeting[length] to check each character until the null character and increments length with ++length.

Practice

1. What is the purpose of the null terminator '\0' in a character array in C++?

easy

A. It marks the end of the string stored in the array.

B. It initializes all characters to zero.

C. It increases the size of the array by one.

D. It converts characters to uppercase.

Solution

1. Step 1: Understand the role of '\0' in character arrays

   The null terminator '\0' is a special character used to mark the end of a string in C++ character arrays.

2. Step 2: Identify its effect on string handling

   Functions that work with strings stop reading characters when they encounter '\0', so it tells where the string ends.

3. Final Answer:

   It marks the end of the string stored in the array. -> Option A

4. Quick Check:

   Null terminator = end of string [OK]

Hint: Remember '\0' ends the string, like a period ends a sentence. [OK]

Common Mistakes:

• Thinking '\0' initializes characters to zero
• Confusing '\0' with increasing array size
• Assuming '\0' changes character case

2. Which of the following is the correct way to declare a character array to hold the word "code" including the null terminator?

easy

A. char word[3] = {'c', 'o', 'd', '\0'};

B. char word[4] = {'c', 'o', 'd', 'e'};

C. char word[4] = "code";

D. char word[5] = {'c', 'o', 'd', 'e', '\0'};

Solution

1. Step 1: Count characters and null terminator

   The word "code" has 4 letters plus 1 null terminator '\0', so the array size must be 5.

2. Step 2: Check each option's array size and initialization

   char word[5] = {'c', 'o', 'd', 'e', '\0'}; correctly declares a char array of size 5 and includes the null terminator explicitly.

3. Final Answer:

   char word[5] = {'c', 'o', 'd', 'e', '\0'}; -> Option D

4. Quick Check:

   Array size = letters + 1 for '\0' [OK]

Hint: Array size = number of chars + 1 for '\0'. [OK]

Common Mistakes:

• Forgetting to add space for the null terminator
• Using incorrect array size
• Not including '\0' explicitly when needed

3. What will be the output of the following C++ code?

char arr[6] = "hello";
arr[0] = 'H';
std::cout << arr << std::endl;

medium

A. hello

B. Hello

C. H

D. Compilation error

Solution

1. Step 1: Understand the initial array content

   The array is initialized with "hello" which includes the null terminator automatically, so arr = {'h','e','l','l','o','\0'}.

2. Step 2: Modify the first character and print

   Changing arr[0] to 'H' updates the first letter. Printing arr outputs the string until '\0', so output is "Hello".

3. Final Answer:

   Hello -> Option B

4. Quick Check:

   Changing arr[0] changes first letter [OK]

Hint: Changing arr[0] changes first letter; output prints until '\0'. [OK]

Common Mistakes:

• Expecting output to be lowercase 'hello'
• Thinking only one character prints
• Assuming compilation error due to modification

4. Identify the error in the following code snippet:

char name[4] = "John";
std::cout << name << std::endl;

medium

A. Incorrect use of double quotes for character array.

B. Missing semicolon after declaration.

C. Array size is too small to hold the string and null terminator.

D. Cannot print character arrays with std::cout.

Solution

1. Step 1: Check array size vs string length

   The string "John" has 4 characters plus a null terminator, so it needs an array of size 5.

2. Step 2: Understand consequences of small array

   Declaring name[4] leaves no space for '\0', causing undefined behavior when printing.

3. Final Answer:

   Array size is too small to hold the string and null terminator. -> Option C

4. Quick Check:

   Array size must include space for '\0' [OK]

Hint: Always add 1 to string length for '\0' in array size. [OK]

Common Mistakes:

• Ignoring null terminator space
• Thinking printing char arrays is invalid
• Confusing syntax errors with size errors

5. You want to store the phrase "Hi!" in a character array and then replace the exclamation mark with a question mark. Which code correctly does this?

hard

A. char phrase[4] = "Hi!";
phrase[2] = '?';
std::cout << phrase << std::endl;

B. char phrase[3] = {'H', 'i', '?'};
std::cout << phrase << std::endl;

C. char phrase[4] = "Hi?";
phrase[3] = '!';
std::cout << phrase << std::endl;

D. char phrase[3] = "Hi!";
phrase[3] = '?';
std::cout << phrase << std::endl;

Solution

1. Step 1: Declare array with correct size for "Hi!"

   The phrase "Hi!" has 3 characters plus 1 for '\0', so array size must be 4.

2. Step 2: Replace '!' with '?' at correct index

   The '!' is at index 2, so phrase[2] = '?' correctly replaces it.

3. Step 3: Print the modified phrase

   Printing phrase outputs "Hi?" as expected.

4. Final Answer:

   char phrase[4] = "Hi!"; phrase[2] = '?'; std::cout << phrase << std::endl; -> Option A

5. Quick Check:

   Array size = 4; replace index 2 [OK]

Hint: Array size = chars + 1; replace character by index. [OK]

Common Mistakes:

• Using array size too small to hold string and '\0'
• Replacing wrong index character
• Confusing initialization with replacement