Character vs string comparison in C++ - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to compare a character variable with a character literal.

C++

char ch = 'a';
if (ch == [1]) {
    std::cout << "Match" << std::endl;
}

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

A"a"

B'b'

C'a'

D"b"

Attempts:

3 left

💡 Hint

Common Mistakes

Using double quotes instead of single quotes for characters.

Characters are compared using single quotes, like 'a'. Double quotes denote strings.

2fill in blank

medium

Complete the code to compare a std::string variable with a string literal.

C++

#include <string>
std::string s = "hello";
if (s == [1]) {
    std::cout << "Equal" << std::endl;
}

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

A"hello"

B'hello'

C'world'

D"world"

Attempts:

3 left

💡 Hint

Common Mistakes

Using single quotes for string literals.

Strings are compared using double quotes, like "hello". Single quotes are for characters.

3fill in blank

hard

Fix the error in the code comparing a char and a string literal.

C++

char ch = 'x';
if (ch == [1]) {
    std::cout << "Yes" << std::endl;
}

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

A'x'

B'y'

C"y"

D"x"

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing char with string literal using double quotes.

Characters must be compared with single quotes, not double quotes which denote strings.

4fill in blank

hard

Fill both blanks to create a map with string keys and char values, filtering keys starting with 'a'.

C++

#include <map>
#include <string>
#include <iostream>

std::map<std::string, char> filtered = {
    {"apple", 'a'},
    {"banana", 'b'},
    {"apricot", 'a'}
};

std::map<std::string, char> result = {
    {k, v} for auto& [k, v] : filtered if k[1] [2] 'a'
};

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

A.at(0)

B[0]

C==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using .at(0) instead of [0].

Using != instead of == for filtering.

To check the first character of a string, use indexing with [0]. To filter keys starting with 'a', use == 'a'.

5fill in blank

hard

Fill all three blanks to create a map of uppercase keys with values greater than 10.

C++

#include <map>
#include <string>
#include <cctype>

std::map<std::string, int> data = {
    {"one", 1},
    {"two", 20},
    {"three", 30}
};

std::map<std::string, int> filtered = {
    [1]: v for (const auto& [k, v] : data) if v [2] 10
};

for (const auto& [k, v] : filtered) {
    std::cout << k << ": " << v << std::endl;
}

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

Ak

B>

Cstd::toupper(k[0]) + k.substr(1)

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using k instead of transformed key.

Using < instead of > for filtering.

To create uppercase keys, transform the first character with std::toupper and append the rest with substr. Filter values greater than 10 using >. Use the original value v in the map.

Practice

1.

Which of the following correctly compares a character ch with another character 'a' in C++?

easy

A. if (ch == string('a'))

B. if (ch == "a")

C. if (ch == 'a')

D. if (ch == char("a"))

Solution

1. Step 1: Understand character vs string literals

   Characters use single quotes like 'a', strings use double quotes like "a".

2. Step 2: Compare character with character

   Comparing ch (char) with 'a' (char) is valid and correct.

3. Final Answer:

   if (ch == 'a') -> Option C

4. Quick Check:

   char == char comparison works directly [OK]

Hint: Use single quotes for chars, double quotes for strings [OK]

Common Mistakes:

• Using double quotes to compare char and string
• Trying to convert char to string incorrectly
• Confusing char and string types

2.

Which of the following is the correct syntax to compare a char variable c with a std::string variable s in C++?

easy

A. if (c == s)

B. if (string(1, c) == s)

C. if (c == s[0])

D. if (c == char(s))

Solution

1. Step 1: Recognize type mismatch

   Directly comparing char and std::string is invalid.

2. Step 2: Convert char to string for comparison

   Use string(1, c) to create a string from the char, then compare with s.

3. Final Answer:

   if (string(1, c) == s) -> Option B

4. Quick Check:

   Convert char to string before comparing with string [OK]

Hint: Convert char to string with string(1, c) before comparing [OK]

Common Mistakes:

• Comparing char directly with string
• Trying to cast string to char
• Using s[0] without checking string length

3.

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

char ch = 'x';
std::string str = "x";
if (ch == str) {
    std::cout << "Equal";
} else {
    std::cout << "Not Equal";
}

medium

A. Compilation error

B. Equal

C. Not Equal

D. Runtime error

Solution

1. Step 1: Analyze comparison types

   Comparing char and std::string directly is not allowed in C++.

2. Step 2: Check compilation rules

   This causes a compilation error because no operator== exists for char and string.

3. Final Answer:

   Compilation error -> Option A

4. Quick Check:

   char == string causes compile error [OK]

Hint: char and string can't be compared directly; causes compile error [OK]

Common Mistakes:

• Assuming char and string compare equal
• Expecting runtime error instead of compile error
• Ignoring type mismatch in comparison

4.

Identify the error in the following code snippet and choose the correct fix:

char c = 'b';
std::string s = "b";
if (c == s[0]) {
    std::cout << "Match";
}

medium

A. No error, code works correctly

B. Change s[0] to s

C. Convert c to string before comparison

D. Use c == s.at(1) instead

Solution

1. Step 1: Understand types in comparison

   c is a char, s[0] is a char (first character of string).

2. Step 2: Check if comparison is valid

   Comparing two chars is valid and works correctly.

3. Final Answer:

   No error, code works correctly -> Option A

4. Quick Check:

   char == s[0] compares chars correctly [OK]

Hint: Compare char with s[0] to compare characters safely [OK]

Common Mistakes:

• Trying to compare char with whole string
• Using s.at(1) which may be out of range
• Converting char to string unnecessarily

5.

You want to check if a char variable ch matches any character in a std::string variable word. Which of the following is the best way to do this in C++?

hard

A. if (ch == word)

B. if (word == string(1, ch))

C. if (ch == word[0])

D. if (word.find(ch) != std::string::npos)

Solution

1. Step 1: Understand the goal

   We want to check if ch appears anywhere inside word.

2. Step 2: Use string find method

   word.find(ch) returns position of ch or std::string::npos if not found.

3. Step 3: Check if found

   If result is not npos, ch is in word.

4. Final Answer:

   if (word.find(ch) != std::string::npos) -> Option D

5. Quick Check:

   Use string::find to check char in string [OK]

Hint: Use word.find(ch) != npos to check char in string [OK]

Common Mistakes:

• Comparing whole string to single char
• Checking only first character with word[0]
• Converting char to string and comparing whole string