Character arrays in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of character array initialization

What is the output of this C++ code snippet?

C++

#include <iostream>
int main() {
    char arr[] = {'H', 'e', 'l', 'l', 'o'};
    std::cout << arr << std::endl;
    return 0;
}

A H

B Compilation error

C Hello

D Random characters or garbage output

💡 Hint

Think about how C++ treats character arrays without a null terminator when printing.

The character array is not null-terminated, so printing it as a C-string leads to undefined behavior and likely garbage output.

❓ Predict Output

intermediate

Output of null-terminated character array

What will this C++ program print?

C++

#include <iostream>
int main() {
    char arr[] = "Hello";
    std::cout << arr << std::endl;
    return 0;
}

A Compilation error

B H

C Hello

D Hello\0

💡 Hint

Remember how string literals are stored in character arrays.

The string literal "Hello" includes a null terminator automatically, so printing arr outputs Hello correctly.

🔧 Debug

advanced

Identify the error in character array usage

What error will this code produce when compiled or run?

C++

#include <iostream>
int main() {
    char arr[5] = "Hello";
    std::cout << arr << std::endl;
    return 0;
}

A Prints Hell

B Compilation error: initializer string too long

C Prints Hello

D Runtime error: buffer overflow

💡 Hint

Check the size of the array vs the string literal length including null terminator.

The string "Hello" requires 6 characters including the null terminator, but the array size is only 5, causing a compilation error.

❓ Predict Output

advanced

Output after modifying character array

What is the output of this program?

C++

#include <iostream>
int main() {
    char arr[] = "Test";
    arr[2] = 'x';
    std::cout << arr << std::endl;
    return 0;
}

A Text

B Texst

C Texs

D Tex

💡 Hint

Look carefully at which character is changed and the original string.

The original string is "Test". Changing arr[2] (the third character) from 's' to 'x' results in "Text".

🧠 Conceptual

expert

Size of character array with null terminator

Given the declaration char arr[] = "Code";, what is the size of arr in bytes?

A 5

B 4

C 6

D Undefined

💡 Hint

Remember that string literals include a null terminator at the end.

The string "Code" has 4 characters plus 1 null terminator, so the array size is 5 bytes.

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