Character vs string comparison in C++ - Practice Questions

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of character and string comparison

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

C++

#include <iostream>
#include <string>

int main() {
    char c = 'a';
    std::string s = "a";
    if (c == s) {
        std::cout << "Equal" << std::endl;
    } else {
        std::cout << "Not Equal" << std::endl;
    }
    return 0;
}

A Compilation error

B Not Equal

C Equal

D Runtime error

💡 Hint

Think about the types being compared: char and std::string.

In C++, you cannot directly compare a char and a std::string using '=='. This causes a compilation error because the types are incompatible.

❓ Predict Output

intermediate

Comparing char with string using c_str()

What is the output of this C++ code?

C++

#include <iostream>
#include <string>
#include <cstring>

int main() {
    char c = 'a';
    std::string s = "a";
    if (std::strcmp(&c, s.c_str()) == 0) {
        std::cout << "Equal" << std::endl;
    } else {
        std::cout << "Not Equal" << std::endl;
    }
    return 0;
}

A Runtime error

B Not Equal

C Equal

D Compilation error

💡 Hint

Consider what &c points to and if it is a proper C-string.

The expression &c points to a single character, but it is not null-terminated. strcmp expects null-terminated strings, so this causes undefined behavior and likely a runtime error.

❓ Predict Output

advanced

Output of comparing char and string with explicit conversion

What is the output of this C++ code?

C++

#include <iostream>
#include <string>

int main() {
    char c = 'a';
    std::string s = "a";
    if (std::string(1, c) == s) {
        std::cout << "Equal" << std::endl;
    } else {
        std::cout << "Not Equal" << std::endl;
    }
    return 0;
}

A Not Equal

B Runtime error

C Compilation error

D Equal

💡 Hint

Look at how the char is converted to a string before comparison.

std::string(1, c) creates a string of length 1 containing the character c. Comparing this string to s which is "a" results in equality.

❓ Predict Output

advanced

Comparing char and string with operator== overload

What is the output of this C++ code?

C++

#include <iostream>
#include <string>

int main() {
    char c = 'a';
    std::string s = "a";
    if (c == s[0]) {
        std::cout << "Equal" << std::endl;
    } else {
        std::cout << "Not Equal" << std::endl;
    }
    return 0;
}

A Runtime error

B Equal

C Compilation error

D Not Equal

💡 Hint

Check what s[0] returns and how it compares to c.

s[0] returns a char, so comparing c and s[0] is a valid char-to-char comparison. Both are 'a', so output is "Equal".

🧠 Conceptual

expert

Why direct char and string comparison fails in C++

Why does the following code fail to compile in C++? char c = 'a'; std::string s = "a"; if (c == s) { // ... } Choose the best explanation.

A Because char variables cannot be used in if statements.

B Because std::string cannot be compared with any other type using operator==.

C Because char and std::string are different types and no operator== overload exists for comparing them directly.

D Because the compiler requires explicit casting of char to int before comparison.

💡 Hint

Think about type compatibility and operator overloading in C++.

C++ does not provide an operator== overload to compare a char directly with a std::string. They are different types, so the compiler cannot resolve the comparison.

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