Character arrays - 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'

A5

B20

C15

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Using a size smaller than needed.

Forgetting the brackets.

The array size must be 10 to hold 10 characters.

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

Chello

D'hello'

Attempts:

3 left

💡 Hint

Common Mistakes

Using single quotes for strings.

Not using quotes at all.

Strings in C must be enclosed in double quotes.

3fill in blank

hard

Fix the error in the code to correctly copy the string "cat" into the character array pet.

C

#include <string.h>

char pet[4];
strcpy(pet, [1]);

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

A'cat'

Bcat

C"cat"

Dpet

Attempts:

3 left

💡 Hint

Common Mistakes

Using single quotes for strings.

Passing a variable name instead of a string.

The string to copy must be a string literal in double quotes.

4fill in blank

hard

Fill both blanks to create a character array greeting initialized with "hi" and print it using printf.

C

#include <stdio.h>

char greeting[[1]] = [2];
printf("%s\n", greeting);

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

A3

B"hi"

C2

D'hi'

Attempts:

3 left

💡 Hint

Common Mistakes

Setting array size too small.

Using single quotes for strings.

The array size must be 3 to hold 'h', 'i', and the null character. The string must be in double quotes.

5fill in blank

hard

Fill all three blanks to declare a character array text, initialize it with "ok", and print its length using strlen.

C

#include <stdio.h>
#include <string.h>

char [1][] = [2];
int length = strlen([3]);
printf("Length: %d\n", length);

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

Atext

B"ok"

Dok

Attempts:

3 left

💡 Hint

Common Mistakes

Using single quotes for strings.

Passing the string literal instead of the array to strlen.

The array name is 'text', initialized with the string "ok", and strlen needs the array name to get length.

Practice

1. What is a character array in C used for?

easy

A. To store a sequence of characters, like a word or sentence

B. To store only numbers

C. To perform mathematical calculations

D. To create a list of integers

Solution

1. Step 1: Understand character arrays

   A character array in C is a collection of characters stored in contiguous memory locations.

2. Step 2: Identify its use

   It is mainly used to store text like words or sentences, not numbers or calculations.

3. Final Answer:

   To store a sequence of characters, like a word or sentence -> Option A

4. Quick Check:

   Character array = text storage [OK]

Hint: Character arrays hold text, not numbers or math [OK]

Common Mistakes:

• Thinking character arrays store numbers only
• Confusing character arrays with integer arrays
• Assuming character arrays perform calculations

2. Which of the following is the correct way to declare a character array to hold the word "hello" in C?

easy

A. char word[6] = "hello";

B. char word[5] = {'h', 'e', 'l', 'l', 'o'};

C. char word[] = {'h', 'e', 'l', 'l', 'o', '\0'};

D. char word[5] = "hello";

Solution

1. Step 1: Understand string termination in C

   Strings in C end with a special character '\0' to mark the end.

2. Step 2: Check array size and initialization

   char word[6] = "hello"; declares an array of size 6 (5 letters + '\0') and initializes it with "hello" correctly.

3. Final Answer:

   char word[6] = "hello"; -> Option A

4. Quick Check:

   String needs space for '\0' [OK]

Hint: Remember to include space for '\0' in string arrays [OK]

Common Mistakes:

• Not allocating space for the null terminator '\0'
• Using single quotes for strings
• Declaring array size too small

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

char str[] = "cat";
printf("%c", str[3]);

medium

A. t

B. 0 (null character, no visible output)

C. c

D. Compilation error

Solution

1. Step 1: Understand string indexing

   String "cat" has characters at indices 0:'c', 1:'a', 2:'t', and index 3 is the null terminator '\0'.

2. Step 2: Print character at index 3

   Printing str[3] prints the null character which is invisible, so no visible output appears.

3. Final Answer:

   0 (null character, no visible output) -> Option B

4. Quick Check:

   str[3] = '\0' (null) [OK]

Hint: Remember strings end with '\0' at last index [OK]

Common Mistakes:

• Expecting 't' at index 3 instead of '\0'
• Thinking it causes an error
• Confusing index positions

4. Identify the error in this code snippet:

char name[5];
strcpy(name, "hello world");

medium

A. No error, code works fine

B. Incorrect use of strcpy function

C. Missing #include <string.h>

D. Array size is too small for the string

Solution

1. Step 1: Check array size vs string length

   "hello world" has 11 characters plus '\0' = 12 total, but array size is only 5.

2. Step 2: Understand consequences

   Copying this string will overflow the array, causing undefined behavior.

3. Final Answer:

   Array size is too small for the string -> Option D

4. Quick Check:

   Array must fit string + '\0' [OK]

Hint: Array size must be >= string length + 1 [OK]

Common Mistakes:

• Ignoring array size limits
• Assuming strcpy checks size
• Forgetting null terminator space

5. Given the code below, what will be the output?

char arr[10] = "abc";
arr[3] = 'd';
arr[4] = '\0';
printf("%s", arr);

hard

A. abc\0d

B. abc

C. abcd

D. Runtime error

Solution

1. Step 1: Analyze initial array content

   arr is initialized with "abc" which is 'a','b','c','\0' plus extra space.

2. Step 2: Modify characters and null terminator

   arr[3] = 'd' adds 'd' after 'c', then arr[4] = '\0' sets new string end after 'd'.

3. Step 3: Print the string

   printf prints characters until '\0', so output is "abcd".

4. Final Answer:

   abcd -> Option C

5. Quick Check:

   String ends at arr[4] '\0' [OK]

Hint: Null terminator controls string end in arrays [OK]

Common Mistakes:

• Ignoring manual null terminator placement
• Expecting original string without changes
• Confusing character and string printing