Character arrays in C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a character array in C++?

A character array is a sequence of characters stored in contiguous memory locations. It is used to store text or strings in C++.

beginner

How do you declare a character array to hold the word "hello"?

You declare it like this:
char word[6] = {'h', 'e', 'l', 'l', 'o', '\0'};
The extra '\0' is the null terminator to mark the end of the string.

beginner

Why is the null terminator '\0' important in character arrays?

The null terminator '\0' tells C++ where the string ends. Without it, functions that work with strings may read beyond the array, causing errors.

beginner

How can you initialize a character array with a string literal?

You can write:
char greeting[] = "hello";
This automatically adds the null terminator and sets the array size to 6.

intermediate

What happens if you forget to add the null terminator in a character array?

The program may read extra garbage characters after the intended string, causing unexpected behavior or crashes.

What does the '\0' character represent in a character array?

A A newline character

B A space character

C A tab character

D The end of the string

The '\0' character is the null terminator that marks the end of a string in a character array.

How do you declare a character array to hold the word "cat" including the null terminator?

A Both B and C

B char cat[4] = "cat";

C char cat[4] = {'c', 'a', 't', '\0'};

D char cat[3] = {'c', 'a', 't'};

Both B and C correctly declare a character array with the word "cat" and the null terminator.

What is the size of the array when you declare char name[] = "Bob";?

A 3

B 4

C 5

D Depends on compiler

The size is 4 because the string "Bob" has 3 characters plus 1 for the null terminator.

Which of these is NOT a correct way to initialize a character array?

A char arr[] = "hello";

B char arr[6] = {'h', 'e', 'l', 'l', 'o', '\0'};

C char arr[5] = "hello";

D char arr[6] = "hello";

Option C is incorrect because the array size 5 is too small to hold the 5 characters plus the null terminator.

What will happen if you print a character array without a null terminator using std::cout?

A It prints characters until it finds a null terminator, possibly reading garbage

B It prints only the characters in the array

C It causes a compile error

D It prints nothing

Without a null terminator, printing may continue past the array boundary, showing garbage characters.

Explain what a character array is and why the null terminator is important.

Think about how C++ knows where the text ends.

Describe two ways to initialize a character array with the word "dog".

One way uses quotes, the other uses braces.

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