String functions overview in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of string find function

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

C++

#include <iostream>
#include <string>

int main() {
    std::string s = "hello world";
    std::cout << s.find("world") << std::endl;
    return 0;
}

A 11

B -1

C 0

D 6

💡 Hint

Remember that string::find returns the index of the first character of the found substring or std::string::npos if not found.

The substring "world" starts at index 6 in "hello world". So s.find("world") returns 6.

❓ Predict Output

intermediate

Result of string substr function

What does this C++ code print?

C++

#include <iostream>
#include <string>

int main() {
    std::string s = "programming";
    std::cout << s.substr(3, 4) << std::endl;
    return 0;
}

A gram

B prog

C ming

D ramm

💡 Hint

substr(pos, len) returns a substring starting at pos with length len.

Starting at index 3 (0-based), the substring of length 4 is "gram".

❓ Predict Output

advanced

Output of string compare function

What is the output of this C++ program?

C++

#include <iostream>
#include <string>

int main() {
    std::string a = "apple";
    std::string b = "apricot";
    std::cout << a.compare(b) << std::endl;
    return 0;
}

A -1

B positive number

C negative number less than -1

D 0

💡 Hint

string::compare returns 0 if equal, positive if first string is lexicographically greater, negative if smaller.

"apple" is lexicographically smaller than "apricot", so compare returns a negative number.

❓ Predict Output

advanced

Effect of string erase function

What is the output of this C++ code?

C++

#include <iostream>
#include <string>

int main() {
    std::string s = "abcdef";
    s.erase(2, 3);
    std::cout << s << std::endl;
    return 0;
}

A abdef

B abf

C abcdef

D ab

💡 Hint

erase(pos, len) removes len characters starting at pos.

Removing 3 characters starting at index 2 removes 'c', 'd', 'e', leaving "abf".

🧠 Conceptual

expert

Behavior of string::npos in find function

What is the value and meaning of std::string::npos in C++ string functions?

A It is the index 0, meaning the start of the string.

B It is a constant representing the maximum possible size_t value, used to indicate 'not found' in string operations.

C It is a negative integer used to indicate an error in string functions.

D It is a boolean true value returned when a substring is found.

💡 Hint

Check the documentation for string::npos and its role in find functions.

std::string::npos is a static constant representing the largest possible size_t value. It signals that a substring was not found.