Lære Challenge: Accessing and Manipulating String Elements

Indexing a string

We can access the elements of a string (which are essentially char characters) using square bracket [] indexing, similar to arrays. This also allows us to replace a character at a specific position.

indexing.h


              12
            
string str = "Cpdefinity"; // Cpdefinity
str[1] = 'o'; // Codefinity

Note

Indexing in a string starts from zero, just like in arrays.

The length of the string

With that indexing, you can try to access a wrong index (that is out of range), and the compiler will tell you nothing about that.

main.cpp


              1234567
            
#include <iostream>

int main()
{
    std::string word = "Codefinity";
    std::cout << word[12]; // Word's length is 10
}

As you can see, the output is unexpected, and C++ does not provide a warning about the issue. To prevent this, you can use the .length() method to determine the length of a string and ensure the index is within the valid range.

main.cpp


              123456789101112
            
#include <iostream>

int main()
{
    std::string word = "Codefinity";
    int index = 12;
    
    if (index >= word.length()) 
	    std::cout << "The output is unexpected!" << std::endl;
    else
        std::cout << word[index]; // Word's length is 10
}

Indexing using method

Another way of indexing is using the .at() method. To get the character with index n, we can use the following syntax:

at.h


              1
            
str.at(n);

It works the same as str[n] but will raise an error if you specify an index that is out of range.

main.cpp


              12345678
            
#include <iostream>

int main()
{
    std::string word = "Codefinity";
    std::cout << word.at(12); // word's length is 10
    // Try outputting the character with the index 5
}

Practice

As was said before, we can replace the characters inside a string using indexing (both with [] and .at()). Here is an example:

main.cpp


              123456789
            
#include <iostream>

int main()
{
    std::string word = "Cpdefinitu";
    word[1] = 'o';
    word.at(word.length() - 1) = 'y'; // length - 1 accesses the last element
    std::cout << word;
}

Opgave

Swipe to start coding

You have an email address as a string. Your task is to mask the username part of the email for privacy.

The function maskEmail takes a string representing the email address.

Inside maskEmail, use the find method to locate the position of the '@' symbol, which marks the end of the username.
Check if the username is longer than 1 character. If not, return the email unchanged.
Use a for loop to iterate from index 1 up to (but not including) the position of '@'.
Within the loop, replace each character with '*' to mask the username.
Return the modified email.

Example

"alex@example.com" => "a***@example.com"
"bob@example.com" => "b**@example.com"
"x@domain.com" => "x@domain.com"

Løsning

solution.cpp

Var alt klart?

Tak for dine kommentarer!

Sektion 3. Kapitel 3

single

Spørg AI

Spørg om hvad som helst eller prøv et af de foreslåede spørgsmål for at starte vores chat

Awesome!

Completion rate improved to 4.35

Stryg for at vise menuen

Indexing a string

indexing.h


              12
            
string str = "Cpdefinity"; // Cpdefinity
str[1] = 'o'; // Codefinity

Note

Indexing in a string starts from zero, just like in arrays.

The length of the string

With that indexing, you can try to access a wrong index (that is out of range), and the compiler will tell you nothing about that.

main.cpp


              1234567
            
#include <iostream>

int main()
{
    std::string word = "Codefinity";
    std::cout << word[12]; // Word's length is 10
}

main.cpp


              123456789101112
            
#include <iostream>

int main()
{
    std::string word = "Codefinity";
    int index = 12;
    
    if (index >= word.length()) 
	    std::cout << "The output is unexpected!" << std::endl;
    else
        std::cout << word[index]; // Word's length is 10
}

Indexing using method

Another way of indexing is using the .at() method. To get the character with index n, we can use the following syntax:

at.h


              1
            
str.at(n);

It works the same as str[n] but will raise an error if you specify an index that is out of range.

main.cpp


              12345678
            
#include <iostream>

int main()
{
    std::string word = "Codefinity";
    std::cout << word.at(12); // word's length is 10
    // Try outputting the character with the index 5
}

Practice

As was said before, we can replace the characters inside a string using indexing (both with [] and .at()). Here is an example:

main.cpp


              123456789
            
#include <iostream>

int main()
{
    std::string word = "Cpdefinitu";
    word[1] = 'o';
    word.at(word.length() - 1) = 'y'; // length - 1 accesses the last element
    std::cout << word;
}

Opgave

Swipe to start coding

You have an email address as a string. Your task is to mask the username part of the email for privacy.

The function maskEmail takes a string representing the email address.

Inside maskEmail, use the find method to locate the position of the '@' symbol, which marks the end of the username.
Check if the username is longer than 1 character. If not, return the email unchanged.
Use a for loop to iterate from index 1 up to (but not including) the position of '@'.
Within the loop, replace each character with '*' to mask the username.
Return the modified email.

Example

"alex@example.com" => "a***@example.com"
"bob@example.com" => "b**@example.com"
"x@domain.com" => "x@domain.com"

Løsning

solution.cpp

Skift til skrivebord for at øve i den virkelige verdenFortsæt der, hvor du er, med en af nedenstående muligheder

Var alt klart?

Tak for dine kommentarer!

Sektion 3. Kapitel 3

single